bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative parallaxes in the massive star forming region W33
Authors: Immer K. , Reid M. J. , Menten K. M. 
Published: July 2012

AbstractThe massive star forming complex W33 contains several molecular clouds at different stages of star formation activity, ranging from quiescent to highly active clouds. Our trigonometric parallax observations of water masers in this complex, conducted with the VLBA at 22.2 GHz, show that all water masers have the same distance of 2.4 kpc, locating the W33 complex in the Sagittarius spiral arm.
3-Dimensional kinematics of water/SiO masers in Orion-KL
Authors: KIM Mi Kyoung , Hirota Tomoya , Hideyuki Kobayashi ,   VERA project team members
Published: July 2012

AbstractResults of multi-epoch VLBI observations toward water/SiO masers in Orion-KL are presented. We conducted high-resolution VLBI observations of water/SiO masers with VERA to probe the structure and the kinematics of the disk/outflow in Orion-KL. The VERA observations provide the positions and proper motions of masers features in Orion-KL with the highest accuracy ever observed. The results of water and SiO maser observations suggest that Source I is a massive YSO with an accretion disk and a collimated outflow.
Mass distribution of the Galaxy with VERA
Authors: Sakai Nobuyuki , Honma Mareki , Nakanishi Hiroyuki , Sakanoue Hirofumi , Kurayama Tomoharu ,   VERA project members
Published: July 2012

AbstractWe aim to reveal the mass distribution of the Galaxy based on a precise rotation curve constructed using VERA observations. We have been observing Galactic H2O masers with VERA. We here report one of the results of VERA for IRAS 05168+3634. The parallax is 0.532 ± 0.053 mas which corresponds to a distance of 1.88+0.21−0.17 kpc, and the proper motions are (μαcosδ, μδ) = (0.23 ± 1.07, −3.14 ± 0.28) mas yr−1. The distance is significantly smaller than the previous distance estimate of 6 kpc based on a kinematic distance. This drastic change places the source in the Perseus arm rather than in the Outer arm. Combination of the distance and the proper motions with the systemic velocity provides a rotation velocity of 227+9−11 km s−1 at the source assuming Θ0 = 240 km s−1. The result is marginally slower than the rotation velocity at LSR with ~ 1−σ significance, but consistent with previous VLBI results for six sources in the Perseus arm. We also show the averaged disk peculiar motion over the seven sources in the Perseus arm as (Umean, Vmean) = (11 ± 3, −17 ± 3) km s−1. It suggests that the seven sources in the Perseus arm are systematically moving toward the Galactic center, and lag behind the Galactic rotation with more than 3-σ significance.
Radio Recombination Line Maser Objects: New Detections with the SMA
Authors: Jiménez-Serra Izaskun 
Published: July 2012

AbstractHydrogen radio recombination line (RRL) masers are a rare phenomenon in star forming regions. Since RRL masers were first detected in 1989 toward the emission line star MWC349A, several single-dish surveys at millimeter wavelengths have been carried out to detect other RRL maser objects. However, although RRL maser amplification is expected to appear at wavelengths <2mm, MWC349A still remains as the only RRL maser object known to date. In this contribution, I will present our recent findings of two new RRL maser objects with the Submillimeter Array (SMA) toward the massive star forming regions Cepheus A HW2 and MonR2-IRS2. Sub-millimeter observations with interferometers such as the SMA and the Atacama Large Millimeter Array (ALMA) open the possibility to detect a much larger sample of RRL maser objects, where very detailed information about the kinematics and physical structure of the innermost ionized regions can be obtained toward these objects.
OH Maser sources in W49N: probing differential anisotropic scattering with Zeeman pairs
Authors: Deshpande Avinash A. , Goss W. M. , Mendoza-Torres J. E. 
Published: July 2012

AbstractOur analysis of a VLBA 12-hour synthesis observations of the OH masers in W49N has provided detailed high angular-resolution images of the maser sources, at 1612, 1665 and 1667 MHz. The images, of several dozens of spots, reveal anisotropic scatter broadening; with typical sizes of a few tens of milli-arc-seconds and axial ratios between 1.5 to 3. The image position angles oriented perpendicular to the galactic plane are interpreted in terms of elongation of electron-density irregularities parallel to the galactic plane, due to a similarly aligned local magnetic field. However, we find the apparent angular sizes on the average a factor of 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred earlier. The average position angle of the scattered broadened images is also seen to deviate significantly (by about 10 degrees) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, we find significant differences in the scatter broadened images for the two hands of polarization, even when apparent velocity separation is less than 0.1 km/s. Here we present the details of our observations and analysis, and discuss the interesting implications of our results for the intervening anisotropic magneto-ionic medium, as well as a comparison with the expectations based on earlier work.
MeerKAT and its potential for Cosmic MASER Research
Authors: Booth Roy , Goedhart Sharmila , Jonas Justin 
Published: July 2012

AbstractThe MeerKAT radio telescope array is the South African precursor instrument for the proposed Square Kilometer Array's mid-band frequency range. It will be the most sensitive centimetre-wavelength telescope in the southern hemisphere until the SKA is built. It will cover a broad range of astronomical science from the evolution of galaxies to tests of Einstein's theory of General Relativity, using Pulsars. The chosen frequency bands will enable sensitive southern Galactic maser surveys in the main lines of hydroxyl, 12 GHz methanol and perhaps 14.5 GHz formaldehyde lines as well as searches for redshifted water masers from red-shifts greater than about 0.5. Proposals for Large Surveys using MeerKAT were solicited in late 2009 and resulted in some 20 proposals from teams comprising 500 scientists, world-wide. The successful proposals relevant to maser research will be discussed below.
KVN Single-dish Water and Methanol Maser Line Surveys of Galactic YSOs
Authors: Kim Kee-Tae , Byun Do-Young , Bae Jae-Han , Kim Won-Ju , Kang Hyun-Woo , Oh Chung Sik , Youn So-Young 
Published: July 2012

AbstractWe have carried out simultaneous 22 GHz H2O and 44 GHz Class I CH3OH maser line surveys of more than 1500 intermediate- and high-mass YSOs in the Galaxy using newly-constructed KVN 21-m telescopes. As the central (proto)stars evolve, the detection rates of the two masers rapidly decrease for intermediate-mass YSOs while the rates increase for high-mass YSOs. These results suggest that the occurrence of the two masers is closely related both to the evolutionary stage of the central objects and to the circumstellar environments. CH3OH masers always have very similar velocities (<10 km s−1) to the natal dense cores, whereas H2O masers often have significantly different velocities. The isotropic luminosities of both masers are well correlated with the bolometric luminosities of the central (proto)stars.
EVLA imaging of the water masers in the massive protostellar cluster NGC6334I
Authors: Hunter Todd R. , Brogan Crystal L. 
Published: July 2012

AbstractWe have used the recently-upgraded Karl G. Jansky Very Large Array (VLA) in A-configuration to observe the water masers in the massive protostellar cluster NGC6334I with broad bandwidth and high spectral resolution. Four groups of maser spots are found. The two groups with the broadest velocity span (40 km/s) are towards the UCHII region and the hot core SMA1. The spatial kinematics of the SMA1 masers are consistent in sense and orientation with the large-scale CO outflow and appear to trace the base of the outflow from a protostar at the dust peak of SMA1. Additional masers at the southern end of SMA1 provide evidence for a second protostar. The highest intensity maser lies about 2″ north of SMA1. Interestingly, no water masers are seen on the equally impressive hot core SMA2. Finally, we have detected maser emission toward the enigmatic source SMA4, which shows no millimeter molecular lines despite having strong, compact submillimeter continuum and may trace another protostar.
Impact of sea‐ice biology on overall primary production in a biophysical model of the pan‐Arctic Ocean
Authors: Dupont Frédéric 
Published: July 2012

The contribution of sea‐ice biology and impact of Arctic warming on overall primary production in a Pan‐Arctic ocean model are investigated in a 57 year (1950–2006) simulation at coarse resolution using a simple ecosystem model. The ice biology model formally represents the growth and aggregation of micro algae into an ice‐water interface, nearly undisturbed by surface mixed layer dynamics. The importance of this so‐called ‘ice‐algae’ stems from their significant contribution to the total primary production (up to 50% depending on the locations, according to observations described in Gosselin et al. (1997). Simple 1D tests reveal that, depending on their initial biomass and light availability, ice algae can affect the temporal variation of surface nutrients, while they marginally impact the total primary production, or the long term position of the nutricline. The sea‐ice primary production is found in the model to be as high as 40% of the total primary production depending on the location and 7.5% for the whole Arctic. The modeled primary production of the ocean is negatively correlated to the September ice cover whereas the production in the ice is more weakly positively correlated. Because of the negative correlation between sea ice cover and pelagic primary production, the short term response to the continuing ice decline will be an increased total production as seen in the model, while the ice algae production would decline.
Paleoceanographic changes in the Eastern Equatorial Pacific over the last 10 Myr
Authors: Seki Osamu , Schmidt Daniela N. , Schouten Stefan , Hopmans Ellen C. , Sinninghe Damsté Jaap S. , Pancost Richard D. 
Published: July 2012

To examine the Late Neogene evolution of tropical Pacific oceanography, we determined multiple geochemical proxy records for temperature (U37K′and TEX86Hindices) and primary productivity (algal biomarkers and diol indices) in sediments recovered at ODP Site 1241 in the East Equatorial Pacific (EEP) spanning a record of the last 10 Myr. The TEX86Htemperatures are lower than those recorded by U37K′indices, exhibiting large fluctuations and suggesting strong warming during the Mid Pliocene Warm Period (MPWP; 4.5–3.2 Ma) and significantly colder temperature during the Late Miocene cooling period (7–5 Ma) and after the Middle Pliocene Warm Period (MPWP). Such variations could reflect changes in the EEP thermocline temperatures, but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure. A combination of temperature records, inferred to represent different and likely varying depths in the water column, as well as algal biomarker records for export production and ecosystem structure, suggest that both productivity and inference upwelling were reduced in the EEP during warmer periods, such as the MPWP and prior to 7 Ma. In contrast, stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 Ma and for the past 3 Myr, both corresponding to globally cool intervals. A further increase in EEP productivity occurred at ca 1.8 Ma, coincident with the development of the E‐W Pacific SST gradient. These results confirm previous work that protracted El Niño–like conditions prevailed during warmer intervals of the Pliocene before ultimately descending into the current climate state.
Seasonal hydrological loading in southern Alaska observed by GPS and GRACE
Authors: Fu Yuning , Freymueller Jeffrey T. , Jensen Tim 
Published: July 2012

We compare vertical seasonal loading deformation observed by continuous GPS stations in southern Alaska and modeled vertical displacements due to seasonal hydrological loading inferred from GRACE. Seasonal displacements are significant, and GPS‐observed and GRACE‐modeled seasonal displacements are highly correlated. We define a measure called the WRMS Reduction Ratio to measure the fraction of the position variations at seasonal periods removed by correcting the GPS time series using a seasonal model based on GRACE. The median WRMS Reduction Ratio is 0.82 and the mean is 0.73 ± 0.26, with a value of 1.0 indicating perfect agreement of GPS and GRACE. The effects of atmosphere and non‐tidal ocean loading are important; we add the AOD1B de‐aliasing model to the GRACE solutions because the displacements due to these loads are present in the GPS data, and this improves the correlations between these two geodetic measurements. We find weak correlations for some stations located in areas where the magnitude of the load changes over a short distance, due to GRACE's limited spatial resolution. GRACE models can correct seasonal displacements for campaign GPS measurements as well.
An avenue of eddies: Quantifying the biophysical properties of mesoscale eddies in the Tasman Sea
Authors: Everett J. D. , Baird M. E. , Oke P. R. , Suthers I. M. 
Published: July 2012

The Tasman Sea is unique ‐ characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast. Through a 16‐year analysis of Tasman Sea eddies, we identify a region along the southeast Australian coast which we name ‘Eddy Avenue’ where eddies have higher sea level anomalies, faster rotation and greater sea surface temperature and chlorophylla anomalies. The density of cyclonic and anticyclonic eddies within Eddy Avenue is 23% and 16% higher respectively than the broader Tasman Sea. We find that Eddy Avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader Tasman Sea, as a result of larger anticyclonic eddies formed from Coral Sea water depressing chl. aconcentrations, and for coastal cyclonic eddies due to the entrainment of nutrient‐rich shelf waters. Cyclonic eddies within Eddy Avenue have almost double the chlorophylla (0.35 mg m−3) of anticyclonic eddies (0.18 mg m−3). The average chlorophyll a concentration for cyclonic eddies is 16% higher in Eddy Avenue and 28% lower for anticyclonic eddies when compared to the Tasman Sea. With a strengthening East Australian Current, the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations.
Spatial distribution of Kelvin‐Helmholtz instability at low‐latitude boundary layer under different solar wind speed conditions
Authors: Li W. Y. , Guo X. C. , Wang C. 
Published: July 2012

Using the PPMLR‐MHD global simulation model, we examined the Kelvin‐Helmholtz (K‐H) instability at the low‐latitude boundary layer (LLBL) under northward interplanetary magnetic field (IMF) conditions with various solar wind speeds (400, 600, and 800 km/s). The spatial distribution of the K‐H wave power in the equatorial plane shows two distinct power populations, referring to the two modes of K‐H surface waves. The spatial evolution of K‐H instability at the boundary layer is classified into four phases: quasi‐stable, exponential growth, linear growth, and nonlinear phases. The boundary layer is quasi‐stable near the subsolar point region. The K‐H instability starts at about 30° longitude, and grows exponentially with a spatial growth rate of 0.28∼0.87 RE−1until ∼45° longitude where the vortices fully develop. At larger longitudes, the instability grows linearly, while the vortices grow in size. From ∼80° longitude to the distant magnetotail, the K‐H instability develops nonlinearly and the vortices roll up. The wave frequency, wavelength, and phase speed are given at various spatial points. Model results show that the higher solar wind speed generates K‐H waves with higher frequency under the northward IMF, and the wavelengths and the phase speeds increase with the increase of the longitude. Moreover, we made a comparison of the K‐H wave periods on Earth's, Mercury's and Saturn's magnetopauses by a proposed prediction method.
Validation of upper mesospheric and lower thermospheric temperatures measured by the Solar Occultation for Ice Experiment
Authors: Stevens Michael H. , Deaver Lance E. , Hervig Mark E. , Russell James M. , Siskind David E. , Sheese Patrick E. , Llewellyn Edward J. , Gattinger Richard L. , Höffner Josef , Marshall B. T. 
Published: July 2012

Temperature observations in the polar mesosphere and lower thermosphere are critical for studies of polar mesospheric cloud (PMC) formation and variability. The Solar Occultation for Ice Experiment (SOFIE) on NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite has been measuring temperatures in the polar atmosphere nearly continuously since 2007. We herein present an improved SOFIE temperature data set and validate it against a variety of satellite and ground‐based observations. We find that when taking all comparisons together, SOFIE temperatures are in agreement with independent observations to within reported systematic uncertainties from 15 to 88 km altitude. Between 88 and 95 km SOFIE temperatures have a warm bias that peaks between 10 and 15 K in the Arctic summer and 20–30 K in the Antarctic summer. Much of the warm bias is likely related to uncertainties in prescribed atomic oxygen densities that are required for the SOFIE temperature retrieval.
High precision, absolute total column ozone measurements from the Pandora spectrometer system: Comparisons with data from a Brewer double monochromator and Aura OMI
Authors: Tzortziou Maria , Herman Jay R. , Cede Alexander , Abuhassan Nader 
Published: July 2012

We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground‐based direct‐sun irradiance measurements using our recently deployed Pandora single‐grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air‐shed and development of a ground‐based monitoring network for studying small‐scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid‐ to high‐latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double‐grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15–80°), indicating adequate Pandora stray light correction. A small (1–2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3°K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura‐OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI‐measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short‐term (hourly) temporal changes in TCO, not possible to capture by sun‐synchronous satellites, such as OMI, alone.
Evapotranspiration along an elevation gradient in California's Sierra Nevada
Authors: Goulden M. L. , Anderson R. G. , Bales R. C. , Kelly A. E. , Meadows M. , Winston G. C. 
Published: July 2012

We combined observations from four eddy covariance towers with remote sensing to better understand the altitudinal patterns of climate, plant phenology, Gross Ecosystem CO2Uptake, and Evapotranspiration (ET) around the Upper Kings River basin in the southern Sierra Nevada Mountains. Precipitation (P) increased with elevation to ∼500 m, and more gradually at higher elevations, while vegetation graded from savanna at 405 m to evergreen oak and pine forest to mid‐montane forest to subalpine forest at 2700 m. CO2uptake and transpiration at 405 m peaked in spring (March to May) and declined in summer; gas exchange at 1160 and 2015 m continued year‐round; gas exchange at 2700 m peaked in summer and ceased in winter. A phenological threshold occurred between 2015 and 2700 m, associated with the development of winter dormancy. Annual ET and Gross Primary Production were greatest at 1160 and 2015 m and reduced at 405 m coincident with less P, and at 2700 m coincident with colder temperatures. The large decline in ET above 2015 m raises the possibility that an upslope redistribution of vegetation with climate change could cause a large increase in upper elevation ET. We extrapolated ET to the entire basin using remote sensing. The 2003–11 P for the entire Upper Kings River basin was 984 mm y−1 and the ET was 429 mm y−1, yielding a P‐ET of 554 mm y−1, which agrees well with the observed Kings River flow of 563 mm y−1. ET averaged across the entire basin was nearly constant from year to year.
Structural origin of polymorphism of Alzheimer's amyloid β-fibrils
Authors: Agopian Audrey , Guo Zhefeng 
Published: July 2012

Formation of senile plaques containing amyloid fibrils of Aβ (amyloid β-peptide) is a pathological hallmark of Alzheimer's disease. Unlike globular proteins, which fold into unique structures, the fibrils of Aβ and other amyloid proteins often contain multiple polymorphs. Polymorphism of amyloid fibrils leads to different toxicity in amyloid diseases and may be the basis for prion strains, but the structural origin for fibril polymorphism is still elusive. In the present study we investigate the structural origin of two major fibril polymorphs of Aβ40: an untwisted polymorph formed under agitated conditions and a twisted polymorph formed under quiescent conditions. Using electron paramagnetic resonance spectroscopy, we studied the inter-strand side-chain interactions at 14 spin-labelled positions in the Aβ40 sequence. The results of the present study show that the agitated fibrils have stronger inter-strand spin–spin interactions at most of the residue positions investigated. The two hydrophobic regions at residues 17–20 and 31–36 have the strongest interactions in agitated fibrils. Distance estimates on the basis of the spin exchange frequencies suggest that inter-strand distances at residues 17, 20, 32, 34 and 36 in agitated fibrils are approximately 0.2 Å (1 Å=0.1 nm) closer than in quiescent fibrils. We propose that the strength of inter-strand side-chain interactions determines the degree of β-sheet twist, which then leads to the different association patterns between different cross β-units and thus distinct fibril morphologies. Therefore the inter-strand side-chain interaction may be a structural origin for fibril polymorphism in Aβ and other amyloid proteins.