39,137 research outputs found
Recommended from our members
The polymeric conformational effect on capacitive deionization performance of graphene oxide/polypyrrole composite electrode
Exploitation of novel faradic materials is an alternative implementation for solving the problem of poor specific electrosorption capacity that conventional carbon materials are encountered in capacitive deionization. Particularly, composite electrode is just a suitable choice because of its potentially high ion-storage ability. Herein, a cyclic voltammetric treatment method with different low limit of potential window was used to manipulate the polymeric conformation and doping level of graphene oxide/polypyrrole (GO/PPy) composite electrode. Based on it, the effect of polymeric structure on the electrosorption performance was systematically studied. When the low limit of potential window is shifted negatively enough, the irreversible polymeric conformational shrinks of GO/PPy are promoted, which not only hinders the insertion process of ions, but also decreases the doping level of polymer due to the intensive interchain-action produced by more entangled polymeric chain. Thus, the number of intercalated ions should decrease, which is expressed by electrochemical impedance spectroscopy (EIS) results and is proportional to the electrosorption capacity of GO/PPy composite electrode in membrane capacitive deionization (MCDI) process. Our work suggests that the less packing density, higher doping level and more charge delocalization on PPy backbone in electrode are beneficial to enhance its capacitive deionization performance
VLBI observation of the newly discovered z=5.18 quasar SDSS J0131-0321
Few high-redshift, radio-loud quasars are known to date. The extremely
luminous, radio-bright quasar, SDSS J013127.34-032100.1 was recently discovered
at a redshift of . We observed the source with high resolution very
long baseline interferometry (VLBI) at 1.7 GHz with the European VLBI Network
(EVN) and found a single compact radio component. We estimated a lower limit to
the brightness temperature of the detected radio component, T_B~10^{11} K.
Additionaly, when compared to archival radio data, the source showed
significant flux density variation. These two findings are indicative of the
blazar nature of the source.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
The Absolute Magnitudes of Red Horizontal Branch Stars in the ugriz System
Based on photometric data of the central parts of eight globular clusters and
one open cluster presented by An and his collaborators, we select red
horizontal branch (RHB) stars in the (g-r)0-g0 diagram and make a statistical
study of the distributions of their colors and absolute magnitudes in the SDSS
ugriz system. Meanwhile, absolute magnitudes in the Johnson VRI system are
calculated through the translation formulae between gri and VRI in the
literature. The calibrations of absolute magnitude as functions of metallicity
and age are established by linear regressions of the data.
It is found that metallicity coefficients in these calibrations decrease,
while age coefficients increase, from the blue filter to the red
filter. The calibration of Mi= 0.06[Fe/H]+0.040t+0.03 has the smallest scatter
of 0.04 mag, and thus i is the best filter in the system when RHB stars
are used for distance indicators. The comparison of the MI calibration from our
data with that from red clump stars indicates that the previous suggestion that
the filter is better than the V filter in distance determination may not be
true because of its significant dependence on age.Comment: 19 pages, 7 figures, accepted by Ap
Sign reversal of field-angle resolved heat capacity oscillations in a heavy fermion superconductor CeCoIn and pairing symmetry
To identify the superconducting gap symmetry in CeCoIn5 (Tc=2.3 K), we
performed angle-resolved specific heat (C_\phi) measurements in a field rotated
around the c-axis down to very low temperatures 0.05Tc and detailed theoretical
calculations. In a field of 1 T, a sign reversal of the fourfold angular
oscillation in C_\phi has been observed at T ~ 0.1Tc on entering a
quasiclassical regime where the maximum of C_\phi corresponds to the antinodal
direction, coinciding with the angle-resolved density of states (ADOS)
calculation. The C_\phi behavior, which exhibits minima along [110] directions,
unambiguously allows us to conclude d_{x^2-y^2} symmetry of this system. The
ADOS-quasiclassical region is confined to a narrow T and H domain within T/Tc ~
0.1 and 1.5 T (0.13Hc2).Comment: 4 pages, 4 figure
The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines
The galaxy 3C\,316 is the brightest in the radio band among the
optically-selected candidates exhibiting double-peaked narrow optical emission
lines. Observations with the Very Large Array (VLA), Multi-Element Remotely
Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN)
at 5\,GHz have been used to study the radio structure of the source in order to
determine the nature of the nuclear components and to determine the presence of
radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent
east-west emission structure with a total extent of about 3 kpc. The EVN image
shows seven discrete compact knots on an S-shaped line. However, none of these
knots could be unambiguously identified as an AGN core. The observations
suggest that the majority of the radio structure belongs to a powerful radio
AGN, whose physical size and radio spectrum classify it as a compact
steep-spectrum source. Given the complex radio structure with radio blobs and
knots, the possibility of a kpc-separation dual AGN cannot be excluded if the
secondary is either a naked core or radio quiet.Comment: 12 pages, 3 figures, 2 tables. Accepted for publication in the MNRA
Four dual AGN candidates observed with the VLBA
According to hierarchical structure formation models, merging galaxies are
expected to be seen in different stages of their coalescence. However,
currently there are no straightforward observational methods neither to select
nor to confirm a large number of dual active galactic nuclei (AGN) candidates.
Most attempts involve the better understanding of double-peaked narrow emission
line sources, to distinguish the objects where the emission lines originate
from narrow-line kinematics or jet-driven outflows from those which might
harbour dual AGN. We observed four such candidate sources with the Very Long
Baseline Array (VLBA) at 1.5 GHz with 10 milli-arcsecond angular
resolution where spectral profiles of AGN optical emission suggested the
existence of dual AGN. In SDSS J210449.13-000919.1 and SDSS J23044.82-093345.3,
the radio structures are aligned with the optical emission features, thus the
double-peaked emission lines might be the results of jet-driven outflows. In
the third detected source SDSS J115523.74+150756.9, the radio structure is less
extended and oriented nearly perpendicular to the position angle derived from
optical spectroscopy. The fourth source remained undetected with the VLBA but
it has been imaged with the Very Large Array at arcsec resolution a few months
before our observations, suggesting the existence of extended radio structure.
In none of the four sources did we detect two radio-emitting cores, a
convincing signature of duality.Comment: 35 pages, 3 figures, 2 tables, accepted for publication in Ap
Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent
Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use 10Be surface exposure ages from four locations between 69.4°N and 61.2°N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 ± 0.2 ka to 10.6 ± 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 ± 0.1 ka to 7.9 ± 0.1 ka in southwest to west Greenland, consistent with existing 10Be ages. At least in south Greenland, these 10Be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures
- …