bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous and High-Resolution Ice-Core Analysis (Abstract)
Authors: Hammer C.U. 
Published: September 2017

The aim of this paper is to evaluate and exemplify the potential of continuous and high-resolution ice-core analysis in atmospheric-climatic research.At present only a few ice-core components of current interest can be measured continuously with high resolution along the cores. In this paper, the techniques of in-situ or “in the laboratory” continuous high-resolution measurement of solid-liquid electrical conductivity, pH, dust and anions will be presented and discussed. In particular, results from individual precipitation samples, seasonal changes, rare events, and the comparison of results from various Antarctic and Greenland ice cores will be discussed.
Chemical Composition of Insoluble Particles in an Ice Cap on Storøya, Svalbard (Abstract)
Authors: Heintzenberg Jost , Källström Margareta , Hansson Hans-Christen , Jonsson Stig 
Published: September 2017

During the Ymer-80 expedition, a 6 m long ice core was taken on the low-lying ice cap Storøyjøkulen, Svalbard. Core samples of about 10 ml were filtered on 0.1 μm pore-size Nuclepore filters, for analysis with a soot photometer and by means of particle-induced X-ray emission, which yielded elemental carbon and about 15 metals in the insoluble microparticles. The concentrationswere comparable to Arctic snow data from other locations. Multivariate statistical analysis of the chemical results indicates two major factors affecting microparticle composition: crustal and anthropogenic. A regular seasonal concentration pattern was found which is consistent with the c. 40 cm annual accumulation deduced from mass-balance studies on the ice cap.
X-Ray Structure Analyses of Air Hydrates in a Deep Ice Core from Dye 3, Greenland (Abstract)
Authors: Hondoh T. , Anzai H. , Hayakawa N. , Mae S. , Higashi A. , Langway C.C. 
Published: September 2017

Clathrate hydrate inclusions of various shapes and sizes were first found by Shoji and Langway (1982) in ice cores from a depth greater than 1280 m at Dye 3, Greenland. Although we have assigned clathrate guest molecules to O2 and N2 by observing Raman spectra of the hydrates in a core from 1501 m depth (Nakahara and others, in press), it has not been determined whether the crystal structure of the hydrate is structure I or structure II.Using the 4-circle diffractometer in the High Brilliance X-ray Laboratory at Hokkaido University, many reflections from the hydrate crystals were identified. Applying extinction rules for cubic crystals, the space group of the hydrate was determined as Fd3m, which corresponded to structure II. The average lattice parameter for a unit cell obtained from three samples was 17.21 A, and this also supports structure II. Structure II was also found with artificial air hydrates by the method of neutron diffraction (Davidson and others 1984).The density of the hydrate was calculated for various combinations of the occupancy of the two types of cage by guest molecules (in a composition ratio of N2 :O2 = (1.5 2.0) : I as determined from Raman intensity). A reasonable value of the density 950 kg m”3 was obtained when only the 12-hedrons were occupied. Therefore it was concluded that the air molecules were trapped only in 12-hedrons which formed the structure II hydrate with 16-hedrons.
Temporal Variations in the Deep Ice-Core Chemistry Record from Dye 3, Greenland (Abstract)
Authors: Langway C.C. , Goto-Azuma K. 
Published: September 2017

Measurements of the chemical constituents in polar-snow deposits translate into chronological records representing a history of atmospheric composition for the periods involved. The 2037 m deep continuous and undisturbed ice core recovered at Dye 3, Greenland between 1979 and 1981 contains a temporal record of sequential snow deposits for the past 9 × 104 a B.P. (Dansgaard and others 1985). The upper 90 m of the deep core were unsuitable for chemistry studies, but stratigraphic continuity with present-day accumulation was obtained by hand-excavating a 5.4 m deep pit and augering two shallow cores to 138 and 113 m depths. The pit and shallow cores represent the last two centuries of snow precipitation.To date, over 6000 individual samples of the pit, shallow and deep ice cores have been measured by ion chromatography for Cl−, NO3−, and SO42− in the field and laboratory (Herron and Langway 1985, Finkel and Langway 1985, Finkel and others 1986), under clean-room conditions. All pit and shallow-core samples were prepared in a continuous sequence of eight samples per year, as identified by other stable and radioactive isotope-dating methods. The deep ice-core samples were selected and prepared from core intervals spaced over the 2037 m profile from time units which showed evidence of abrupt or transitory periods in climate change or volcanic disturbances, as defined by stable isotopes (Dansgaard and others 1985), atmospheric gases (Oeschger and others 1985) and dust (Hammer and others 1985).Approximately 1700 new measurements from the Dye 3 samples are included in this study. Variability in the chemical constituents and their concentration levels is present and meaningful on a short-term and long-term basis. The time units measured represent seasons, years, decades, centuries and longer geological periods. Particular attention is given to two new high- and low-frequency detailed chronological data sets from (1) a continuous 26 m core profile, representing 3000 years, extending from the Holocene/Wisconsin boundary back into the late Wisconsin and (2) measurements made on 106 samples spaced every 2 m over the Wisconsin-age ice from 1786 to 2008 m.
Dielectric Properties of Deep Ice Cores with Air-Hydrate Inclusions (Abstract)
Authors: Mae Shinji , Hondoh Takeo , Nakawo Masayoshi , Langway C.C. 
Published: September 2017

Air-hydrate inclusions have been found in deep ice cores from Dye 3, Greenland, which were taken in August 1981. Although the concentration of the air-hydrate crystals decreased with time, when the core was stored at a temperature of −50 °C, they still existed to an appreciable extent in 1985.An ice specimen was cut out from the Dye 3 core at a depth of 1500 m, where the volume fraction of the hydrate crystals was about 10−3 by volume. Its dielectric properties were measured in September 1985, in a frequency range of 30-20 × 103 Hz and temperature range of −20° to −90°C. The activation energy obtained for the relaxation time of the Debye dispersion was about 0.2 eV, which is much smaller than that of pure ice.The measurement was repeated once a month for about a year, and the sample was stored at a temperature of −10 °C between measurements. The time variation of the dielectric properties has been discussed in relation to the deterioration of the air-hydrate crystals.
Gas Diffusion and Fractionation in Clathrated Ice-Core Samples (Abstract)
Authors: Ocampo J. 
Published: September 2017

The evolution of gas content from clathrated ice is very sensitive to pressure and to storage temperature. As such substances are likely to be found in deep Antarctic ice and the Greenland ice sheet (Miller 1969, Shoji and Langway 1982), the influence of clathrate formation and incomplete back-diffusion on the measured air composition was investigated.We have undertaken laboratory studies on the kinetics of formation and decomposition of clathrate hydrates of air and carbon dioxide. The kinetics were found to be controlled mainly by the self-diffusion of water molecules. The clathrate structure being of type II (Davidson and others 1984), the diffusion of guest molecules and the role of auxiliary gases was studied.A bubble-relaxation model is presented for air-hydrate inclusions in fresh ice cores. It takes into account the diffusion constant for desorption of clathrates and the mechanical relaxation of the bulk ice. The increasing pressure and the initially low bubble surface are factors which limit the rate of decomposition. The rate of decomposition was compared with the natural bubble relaxation measured in deep ice cores (Gow and Williamson 1975).Fractionation was also observed through the formation and decomposition of mixed hydrates. The diffusion control of the recrystallization process affects this fractionation.On the basis of this study we make some recommendations for the analysis of deep ice-core samples.
N2O Measurements on Air Extracted from Antarctic Ice Cores (Abstract)
Authors: Zardini D. , Raynaud D. , Scharffe D. , Seiler W. 
Published: September 2017

A method has been developed for measuring N2O concentrations in the air extracted from the bubbles contained in ice cores. The air extraction is performed by cutting the ice into very small pieces with a rotating knife, in a controlled atmosphere. The N2O concentrations are measured by gas chromatography. The complete original procedure will be discussed, and the results of the different experimental tests given, with a discussion of the uncertainties.This method has been used to perform about 40 measurements on Antarctic ice samples. Ten air samples from the D57 core date approximately from the beginning of the seventeenth and twentieth centuries. The others were taken from the Dome C core and date from the Holocene and the period around the Last Glacial Maximum. The D57 results are in agreement with those of Pearman and others (1986), leading to a similar pre-industrial N2O level (270-290 ppb volume). Furthermore, our Dome C results suggest that during the Last Glacial Maximum atmospheric N2O content was not drastically different from the recent period.
The Infall of the Virgo Elliptical Galaxy M60 toward M87 and the Gaseous Structures Produced by Kelvin–Helmholtz Instabilities
Authors: Wood R. A. , Jones C. , Machacek M. E. , Forman W. R. , Bogdan A. , Andrade-Santos F. , Kraft R. P. , Paggi A. , Roediger E. 
Published: September 2017

Abstract
We present Chandra observations of hot gas structures, which are characteristic of gas-stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. Chandra X-ray images at 0.5–2 keV show a sharp leading edge in the surface brightness that is 12.4 ± 0.1 kpc north and west of the galaxy center in the direction of M87 and characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00 ± 0.02 keV for an abundance of

inside the edge and

for an abundance of

in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio

between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of

and Mach number of

. For 1.37 keV Virgo gas, we find a total infall velocity for M60 of

. We calculate the motion in the plane of the sky to be

, implying an inclination angle of

°. Surface brightness profiles also show the presence of a faint, diffuse gaseous tail. We identify filamentary gaseous wing structures caused by the galaxy’s motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin–Helmholtz instabilities, as expected if the gas-stripping is close to inviscid.
Relativistic Gas Drag on Dust Grains and Implications
Authors: Hoang Thiem 
Published: September 2017

Abstract
We study the drag force on grains moving at relativistic velocities through interstellar gas and explore its application. First, we derive a new analytical formula of the drag force at high energies and find that it is significantly reduced compared to the classical model. Second, we apply the obtained drag force to calculate the terminal velocities of interstellar grains by strong radiation sources such as supernovae and active galactic nuclei (AGNs). We find that grains can be accelerated to relativistic velocities by very luminous AGNs. We then quantify the deceleration of relativistic spacecraft proposed by the Breakthrough Starshot initiative due to gas drag on a relativistic lightsail. We find that the spacecraft’s decrease in speed is negligible because of the suppression of gas drag at relativistic velocities, suggesting that the lightsail may be open for communication during its journey to α Centauri without causing a considerable delay. Finally, we show that the damage to relativistic thin lightsails by interstellar dust is a minor effect.
Wavelet Denoising of Radio Observations of Rotating Radio Transients (RRATs): Improved Timing Parameters for Eight RRATs
Authors: Jiang M. , Cui B.-Y. , Schmid N. A. , McLaughlin M. A. , Cao Z.-C. 
Published: September 2017

Abstract
Rotating radio transients (RRATs) are sporadically emitting pulsars detectable only through searches for single pulses. While over 100 RRATs have been detected, only a small fraction (roughly 20%) have phase-connected timing solutions, which are critical for determining how they relate to other neutron star populations. Detecting more pulses in order to achieve solutions is key to understanding their physical nature. Astronomical signals collected by radio telescopes contain noise from many sources, making the detection of weak pulses difficult. Applying a denoising method to raw time series prior to performing a single-pulse search typically leads to a more accurate estimation of their times of arrival (TOAs). Taking into account some features of RRAT pulses and noise, we present a denoising method based on wavelet data analysis, an image-processing technique. Assuming that the spin period of an RRAT is known, we estimate the frequency spectrum components contributing to the composition of RRAT pulses. This allows us to suppress the noise, which contributes to other frequencies. We apply the wavelet denoising method including selective wavelet reconstruction and wavelet shrinkage to the de-dispersed time series of eight RRATs with existing timing solutions. The signal-to-noise ratio (S/N) of most pulses are improved after wavelet denoising. Compared to the conventional approach, we measure 12%–69% more TOAs for the eight RRATs. The new timing solutions for the eight RRATs show 16%–90% smaller estimation error of most parameters. Thus, we conclude that wavelet analysis is an effective tool for denoising RRATs signal.
Chemical Abundances and Ages of the Bulge Stars in APOGEE High-velocity Peaks
Authors: Zhou Yingying , Shen Juntai , Liu Chao , Li Zhao-Yu , Mao Shude , Kunder Andrea , Rich R. Michael , Zasowski G. , Fernandez-Trincado J. G. , Majewski Steven R. , Lin Chien-Cheng , Geisler Doug , Tang Baitian , Villanova S. , Roman-Lopes A. , Schultheis M. , Nidever David L. , Meza Andrés , Pan Kaike , Bizyaev D. V. 
Published: September 2017

Abstract
A cold, high-velocity (HV, ∼200 km s−1) peak was first reported in several Galactic bulge fields based on the Apache Point Observatory Galaxy Evolution Experiment (APOGEE) commissioning observations. Both the existence and the nature of the HV peak are still under debate. Here we revisit this feature with the latest APOGEE DR13 data. We find that most of the low-latitude bulge fields display a skewed Gaussian distribution with an HV shoulder. However, only 3 out of 53 fields show distinct HV peaks around 200 km s−1. The velocity distribution can be well described by Gauss–Hermite polynomials, except for the three fields showing clear HV peaks. We find that the correlation between the skewness parameter (h
3) and the mean velocity (

), instead of a distinctive HV peak, is a strong indicator of the bar. It was recently suggested that the HV peak is composed of preferentially young stars. We choose three fields showing clear HV peaks to test this hypothesis using the metallicity, [α/M], and [C/N] as age proxies. We find that both young and old stars show HV features. The similarity between the chemical abundances of stars in the HV peaks and the main component indicates that they are not systematically different in terms of chemical abundance or age. In contrast, there are clear differences in chemical space between stars in the Sagittarius dwarf and the bulge stars. The strong HV peaks off-plane are still to be explained properly and could be different in nature.
Toroidal–Poloidal Magnetic Field Generation in Neutron Stars by Spacetime Frame-dragging
Authors: Mirza Babur M. 
Published: September 2017

Abstract
Neutron star magnetic fields, particularly in magnetars, have strong poloidal and toroidal components, reaching magnitudes up to

and extending into the magnetosphere, where they cause twisted magnetic fields and surface currents. Here, we show that to a large extent neutron star toroidal and poloidal magnetic fields are due to frame-dragging of spacetime in the stellar exterior. In the explicit case of linearized Kerr metric we show that general relativistic Maxwell equations admit a mixed poloidal and toroidal magnetic field configuration in which the toroidal field strength is comparable with the poloidal magnetic field. Calculations are performed to show that the frame-dragging-induced magnetic field has the observed order of magnitude at the stellar surface, and exhibits the flare-like phenomenon observed in magnetars.
Mira Variable Stars from LAMOST DR4 Data: Emission Features, Temperature Types, and Candidate Selection
Authors: Yao Yuhan , Liu Chao , Deng Licai , de Grijs Richard , Matsunaga Noriyuki 
Published: September 2017

Abstract
Based on an extensive spectral study of a photometrically confirmed sample of Mira variables, we find a relationship between the relative Balmer emission-line strengths and spectral temperatures of O-rich Mira stars. The

flux ratio increases from less than unity to five as stars cool down from M0 to M10, which is likely driven by increasing TiO absorption above the deepest shock-emitting regions. We also discuss the relationship between the equivalent widths of the Balmer emission lines and the photometric luminosity phase of our Mira sample stars. Using our 291 Mira spectra as templates for reference, 191 Mira candidates are newly identified from the LAMOST DR4 catalog. We summarize the criteria adopted to select Mira candidates based on emission-line indices and molecular absorption bands. This enlarged spectral sample of Mira variables has the potential to contribute significantly to our knowledge of the optical properties of Mira stars and will facilitate further studies of these late-type, long-period variables.
Broadband Spectral Investigations of Magnetar Bursts
Authors: Kırmızıbayrak Demet , Şaşmaz Muş Sinem , Kaneko Yuki , Göğüş Ersin 
Published: September 2017

Abstract
We present our broadband (2–250 keV) time-averaged spectral analysis of 388 bursts from SGR J1550−5418, SGR 1900+14, and SGR 1806−20 detected with the Rossi X-ray Timing Explorer (RXTE) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6% of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.
Kinetic Alfvén Turbulence: Electron and Ion Heating by Particle-in-cell Simulations
Authors: Hughes R. Scott , Gary S. Peter , Wang Joseph , Parashar Tulasi N. 
Published: September 2017

Abstract
Three-dimensional particle-in-cell simulations of the forward cascade of decaying kinetic Alfvén turbulence have been carried out as an initial-value problem on a collisionless, homogeneous, magnetized, electron–ion plasma model with

and m
i/m
e = 100, where subscripts e and i represent electrons and ions, respectively. Initial anisotropic narrowband spectra of relatively long-wavelength modes with approximately gyrotropic distributions in

undergo a forward cascade to broadband spectra of magnetic fluctuations at shorter wavelengths. Maximum electron and ion heating rates are computed as functions of the initial fluctuating magnetic field energy density

on the range

. In contrast to dissipation by whistler turbulence, the maximum ion heating rate due to kinetic Alfvén turbulence is substantially greater than the maximum electron heating rate. Furthermore, ion heating as well as electron heating due to kinetic Alfvén turbulence scale approximately with ε
o. Finally, electron heating leads to anisotropies of the type

, where the parallel and perpendicular symbols refer to directions parallel and perpendicular, respectively, to the background magnetic field, whereas the heated ions remain relatively isotropic. This implies that, for the range of ε
o values considered, the Landau wave–particle resonance is a likely heating mechanism for the electrons and may also contribute to ion heating.
Simulating Gamma-Ray Emission in Star-forming Galaxies
Authors: Pfrommer Christoph , Pakmor Rüdiger , Simpson Christine M. , Springel Volker 
Published: September 2017

Abstract
Star-forming galaxies emit GeV and TeV gamma-rays that are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. To understand the emission, we have used the moving-mesh code Arepo to perform magnetohydrodynamical galaxy formation simulations with self-consistent CR physics. Our galaxy models exhibit a first burst of star formation that injects CRs at supernovae. Once CRs have sufficiently accumulated in our Milky Way–like galaxy, their buoyancy force overcomes the magnetic tension of the toroidal disk field. As field lines open up, they enable anisotropically diffusing CRs to escape into the halo and to accelerate a bubble-like, CR-dominated outflow. However, these bubbles are invisible in our simulated gamma-ray maps of hadronic pion-decay and secondary inverse-Compton emission because of low gas density in the outflows. By adopting a phenomenological relation between star formation rate (SFR) and far-infrared emission and assuming that gamma-rays mainly originate from decaying pions, our simulated galaxies can reproduce the observed tight relation between far-infrared and gamma-ray emission, independent of whether we account for anisotropic CR diffusion. This demonstrates that uncertainties in modeling active CR transport processes only play a minor role in predicting gamma-ray emission from galaxies. We find that in starbursts, most of the CR energy is “calorimetrically” lost to hadronic interactions. In contrast, the gamma-ray emission deviates from this calorimetric property at low SFRs due to adiabatic losses, which cannot be identified in traditional one-zone models.