367 research outputs found
IC 225: a dwarf elliptical galaxy with a peculiar blue core
We present the discovery of a peculiar blue core in the elliptical galaxy IC
225 by using images and spectrum from the Sloan Digital Sky Survey (SDSS). The
outer parts of the surface brightness profiles of u-, g-, r-, i- and z-band
SDSS images for IC 225 are well fitted with an exponential function. The
fitting results show that IC 225 follows the same relations between the
magnitude, scale length and central surface brightness for dwarf elliptical
galaxies. Its absolute blue magnitude (M_B) is -17.14 mag, all of which suggest
that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile
indicates a very blue core with a radius of 2 arcseconds, which is also clearly
seen in the RGB image made of g-, r- and i-band SDSS images. The SDSS optical
spectrum exhibits strong and very narrow nebular emission lines. The metal
abundances derived by the standard methods, which are 12+log(O/H) = 8.98,
log(N/O) = -0.77 and 12+log(S+/H+) = 6.76, turn out to be significantly higher
than that predicted by the well-known luminosity-metallicity relation. After
carefully inspecting the central region of IC 225, we find that there are two
distinct nuclei, separated by 1.4 arcseconds, the off-nucleated one is even
bluer than the nucleus of IC 225. The asymmetric line profiles of higher-order
Balmer lines indicate that the emission lines are bluer shifted relative to the
absorption lines, suggesting that the line emission arises from the off-center
core, whose nature is a metal-rich Hii region. To the best of our knowledge, it
is the first high-metallicity Hii region detected in a dwarf elliptical galaxy.Comment: 7 figures, accepted for publication in A
The on-top pair-correlation density in the homogeneous electron liquid
The ladder theory, in which the Bethe-Goldstone equation for the effective
potential between two scattering particles plays a central role, is well known
for its satisfactory description of the short-range correlations in the
homogeneous electron liquid. By solving exactly the Bethe-Goldstone equation in
the limit of large transfer momentum between two scattering particles, we
obtain accurate results for the on-top pair-correlation density , in both
three dimensions and two dimensions. Furthermore, we prove, in general, the
ladder theory satisfies the cusp condition for the pair-correlation density
at zero distance .Comment: 8 pages, 4 figure
Theories of reasoning and focal point play with a matched non-student sample
We present a coordination game experiment testing the robustness of the predictive power of level-k reasoning and team reasoning in a sample of Chinese tax administrators that is matched for likely socio-economic characteristics with our student sample. We show how the incidence of coordination game play is virtually identical between Chinese tax administrators and university students. However, relatively to non-students, students are comparatively more attracted by the focal point under team reasoning when this has equal payoffs and the other outcomes do not
All-fibre heterogeneously-integrated frequency comb generation using silicon core fibre.
Originally developed for metrology, optical frequency combs are becoming increasingly pervasive in a wider range of research topics including optical communications, spectroscopy, and radio or microwave signal processing. However, application demands in these fields can be more challenging as they require compact sources with a high tolerance to temperature variations that are capable of delivering flat comb spectra, high power per tone, narrow linewidth and high optical signal-to-noise ratio. This work reports the generation of a flat, high power frequency comb in the telecom band using a 17 mm fully-integrated silicon core fibre as a parametric mixer. Our all-fibre, cavity-free source combines the material benefits of planar waveguide structures with the advantageous properties of fibre platforms to achieve a 30 nm bandwidth comb source containing 143 tones with 30 dB OSNR over the entire spectral region
Homodyne OFDM with Optical Injection Locking for Carrier Recovery
Homodyne detection provides the simplest digital signal processing (DSP) solution to optical coherent detection and minimizes the receiver bandwidth requirements. These features make it promising for high spectrally-efficient formats such as Optical Orthogonal Frequency Domain Multiplexing (OFDM), which has a flat optical spectrum and which is thus inherently sensitive to high frequency distortions, e.g., due to limited detector bandwidth. The key to homodyne detection is recovery of the carrier from the received signal all optically (as opposed to frequency offset compensation via digital signal processing. Herein we use optical injection locking (OIL) in conjunction with carrier tone-assisted OFDM to achieve this. In contrast to previous reports, we show that OIL carrier recovery with subsequent homodyne detection can operate without the need for any optical pre-filtering. First, we evaluate the performance as a function of the carrier tone guardband bandwidth. Further, we improve the robustness of this technique using a slow phase lock loop that compensates for drift in the laser’s temperature/current control electronics. Using this improved setup, we compare our all-optical-carrier-recovered homodyne and the ‘traditional’ DSP-assisted intradyne detection for the case of OFDM-16QAM signals. Finally, we compare the computing complexity necessary for both approaches and estimate the intradyne performance limitations due to the carrier-local oscillator frequency offse
Quantum Interference Enhances the Performance of Single-Molecule Transistors
An unresolved challenge facing electronics at a few-nm scale is that
resistive channels start leaking due to quantum tunneling. This affects the
performance of nanoscale transistors, with single-molecule devices displaying
particularly low switching ratios and operating frequencies, combined with
large subthreshold swings.1 The usual strategy to mitigate quantum effects has
been to increase device complexity, but theory shows that if quantum effects
are exploited correctly, they can simultaneously lower energy consumption and
boost device performance.2-6 Here, we demonstrate experimentally how the
performance of molecular transistors can be improved when the resistive channel
contains two destructively-interfering waves. We use a zinc-porphyrin coupled
to graphene electrodes in a three-terminal transistor device to demonstrate a
>104 conductance-switching ratio, a subthreshold swing at the thermionic limit,
a > 7 kHz operating frequency, and stability over >105 cycles. This performance
is competitive with the best nanoelectronic transistors. We fully map the
antiresonance interference features in conductance, reproduce the behaviour by
density functional theory calculations, and trace back this high performance to
the coupling between molecular orbitals and graphene edge states. These results
demonstrate how the quantum nature of electron transmission at the nanoscale
can enhance, rather than degrade, device performance, and highlight directions
for future development of miniaturised electronics.Comment: 11 pages, 4 figure
Phase-Coherent Charge Transport through a Porphyrin Nanoribbon
Quantum interference in nano-electronic devices could lead to reduced-energy
computing and efficient thermoelectric energy harvesting. When devices are
shrunk down to the molecular level it is still unclear to what extent electron
transmission is phase coherent, as molecules usually act as scattering centres,
without the possibility of showing particle-wave duality. Here we show electron
transmission remains phase coherent in molecular porphyrin nanoribbons,
synthesized with perfectly defined geometry, connected to graphene electrodes.
The device acts as a graphene Fabry-P\'erot interferometer, allowing direct
probing of the transport mechanisms throughout several regimes, including the
Kondo one. Electrostatic gating allows measurement of the molecular conductance
in multiple molecular oxidation states, demonstrating a thousand-fold increase
of the current by interference, and unravelling molecular and graphene
transport pathways. These results demonstrate a platform for the use of
interferometric effects in single-molecule junctions, opening up new avenues
for studying quantum coherence in molecular electronic and spintronic devices.Comment: 14 pages, 3 figure
A global multiproxy database for temperature reconstructions of the Common Era
Reproducible climate reconstructions of the Common Era (1 CE to present) are
key to placing industrial-era warming into the context of natural climatic
variability. Here we present a community-sourced database of temperature-
sensitive proxy records from the PAGES2k initiative. The database gathers 692
records from 648 locations, including all continental regions and major ocean
basins. The records are from trees, ice, sediment, corals, speleothems,
documentary evidence, and other archives. They range in length from 50 to 2000
years, with a median of 547 years, while temporal resolution ranges from
biweekly to centennial. Nearly half of the proxy time series are significantly
correlated with HadCRUT4.2 surface temperature over the period 1850–2014.
Global temperature composites show a remarkable degree of coherence between
high- and low-resolution archives, with broadly similar patterns across
archive types, terrestrial versus marine locations, and screening criteria.
The database is suited to investigations of global and regional temperature
variability over the Common Era, and is shared in the Linked Paleo Data (LiPD)
format, including serializations in Matlab, R and Python
Whole Genome Distribution and Ethnic Differentiation of Copy Number Variation in Caucasian and Asian Populations
Although copy number variation (CNV) has recently received much attention as a form of structure variation within the human genome, knowledge is still inadequate on fundamental CNV characteristics such as occurrence rate, genomic distribution and ethnic differentiation. In the present study, we used the Affymetrix GeneChip® Mapping 500K Array to discover and characterize CNVs in the human genome and to study ethnic differences of CNVs between Caucasians and Asians. Three thousand and nineteen CNVs, including 2381 CNVs in autosomes and 638 CNVs in X chromosome, from 985 Caucasian and 692 Asian individuals were identified, with a mean length of 296 kb. Among these CNVs, 190 had frequencies greater than 1% in at least one ethnic group, and 109 showed significant ethnic differences in frequencies (p<0.01). After merging overlapping CNVs, 1135 copy number variation regions (CNVRs), covering approximately 439 Mb (14.3%) of the human genome, were obtained. Our findings of ethnic differentiation of CNVs, along with the newly constructed CNV genomic map, extend our knowledge on the structural variation in the human genome and may furnish a basis for understanding the genomic differentiation of complex traits across ethnic groups
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