157 research outputs found
Evidence for Dirac Fermions in a honeycomb lattice based on silicon
Silicene, a sheet of silicon atoms in a honeycomb lattice, was proposed to be
a new Dirac-type electron system similar as graphene. We performed scanning
tunneling microscopy and spectroscopy studies on the atomic and electronic
properties of silicene on Ag(111). An unexpected
reconstruction was found, which is explained by an extra-buckling model.
Pronounced quasi-particle interferences (QPI) patterns, originating from both
the intervalley and intravalley scattering, were observed. From the QPI
patterns we derived a linear energy-momentum dispersion and a large Fermi
velocity, which prove the existence of Dirac Fermions in silicene.Comment: 6 pages, 4 figure
Discovering strongly lensed quasar candidates with catalogue-based methods from DESI Legacy Surveys
The Hubble tension, revealed by a discrepancy between
measurements of the Hubble-Lemaitre constant from early- and local-Universe
observations, is one of the most significant problems in modern cosmology. In
order to better understand the origin of this mismatch, independent techniques
to measure , such as strong lensing time delays, are required. Notably,
the sample size of such systems is key to minimising statistical uncertainties
and cosmic variance, which can be improved by exploring the datasets of
large-scale sky surveys like DESI (Dark Energy Spectroscopic Instrument). We
identify possible strong lensing time-delay systems within DESI by selecting
candidate multiply imaged lensed quasars from a catalogue of 24,440,816
candidate QSOs contained in the 9th data release of the DESI Legacy Imaging
Surveys (DESI-LS). Using a friend-of-friends-like algorithm on spatial
co-ordinates, our method generates an initial list of compact quasar groups.
This list is subsequently filtered using a measure of the similarity of colours
of a group's members and the likelihood that they are quasars. A visual
inspection finally selects candidate strong lensing systems based on the
spatial configuration of the group members. We identify 620 new candidate
multiply imaged lensed quasars (101 Grade-A, 214 Grade-B, 305 Grade-C). This
number excludes 53 known spectroscopically confirmed systems and existing
candidate systems identified in other similar catalogues. When available, these
new candidates will be further checked by combining the spectroscopic and
photometric data from DESI. The catalogues and images of the candidates in this
work are available online
(https://github.com/EigenHermit/lensed_qso_cand_catalogue_He-22/).Comment: Accepted by A&A. 14 pages, 11 figures. Comments are welcom
Expression and characterization of UL16 gene from duck enteritis virus
<p>Abstract</p> <p>Background</p> <p>Previous studies have indicated that the UL16 protein and its homologs from herpesvirus were conserved and played similar roles in viral DNA packaging, virion assembly, budding, and egress. However, there was no report on the UL16 gene product of duck enteritis virus (DEV). In this study, we analyzed the amino acid sequence of UL16 using bioinformatics tools and expressed in <it>Escherichia coli </it>Rosetta (DE3) induced by isopropy1-β-D-thiogalactopyranoside (IPTG). The recombinant protein was produced, purified using a Ni-NTA column and used to generate the polyclonal antibody against UL16. The intracellular distribution of the DEV UL16 product was carried out using indirect immunofluorescence assay.</p> <p>Results</p> <p>In our study, UL16 gene of DEV was composed of 1089 nucleotides, which encoded 362 amino acids. Multiple sequence alignment suggested that the UL16 gene was highly conserved in herpesvirus family. The UL16 gene was cloned into a pET prokaryotic expression vector and transformed into <it>Escherichia coli </it>Rossetta (DE3) induced by IPTG. A 60kDa fusion protein band corresponding to the predicted size was produced on the SDS-PAGE, purified using a Ni-NTA column. Anti-UL16 polyclonal sera was prepared by immunizing rabbits, and reacted with a band in the IPTG induced cell lysates with an apparent molecular mass of 60 kDa. In vivo expression of the UL16 protein in DEV infected duck embryo fibroblast cells (DEFs) was localized mostly around perinuclear cytoplasmic area and in cytosol using indirect immunofluorescence assay.</p> <p>Conclusions</p> <p>The UL16 gene of DEV was successfully cloned, expressed and detected in DEV infected DEFs for the first time. The UL16 protein localized mostly around perinuclear cytoplasmic area and in cytosol in DEV infected DEFs. DEV UL16 shared high similarity with UL16 family members, indicating that DEV UL16 many has similar function with its homologs. All these results may provide some insight for further research about full characterizations and functions of the DEV UL16.</p
Scanning For Dark Matter Subhalos in Hubble Space Telescope Imaging of 54 Strong Lenses
The cold dark matter (DM) model predicts that every galaxy contains thousands
of DM subhalos; almost all other DM models include a physical process that
smooths away the subhalos. The subhalos are invisible, but could be detected
via strong gravitational lensing, if they lie on the line of sight to a
multiply-imaged background source, and perturb its apparent shape. We present a
predominantly automated strong lens analysis framework, and scan for DM
subhalos in Hubble Space Telescope imaging of 54 strong lenses. We identify two
compelling DM subhalo candidates (including one previously found in
SLACS0946+1006), where a subhalo is favoured after every systematic test we
perform. We find that the detectability of subhalos depends upon the assumed
parametric form for the lens galaxy's mass distribution. Comparing fits which
assume several more complex mass models reveals additional (generally lower
mass) DM subhalo candidates worthy of further study, and the removal of 7 false
positives. We identify 38 non-detections, which are vital to building up enough
statistical power to test DM models. Future work will apply even more flexible
models to the results of this study, to constrain different DM models. Our full
analysis results are available at
https://github.com/Jammy2211/autolens_subhalo.Comment: 25 Pages, 15 Figure
Beyond the bulge–halo conspiracy? Density profiles of early-type galaxies from extended-source strong lensing
Observations suggest that the dark matter and stars in early-type galaxies ‘conspire’ to produce a surprisingly simple distribution of total mass, ρ(r) ∝ ρ−γ, with γ ≈ 2. We measure the distribution of mass in 48 early-type galaxies that gravitationally lens a resolved background source. By fitting the source light in every pixel of images from the Hubble Space Telescope, we find a mean ⟨γ⟩=2.075+0.023−0.024 with an intrinsic scatter between galaxies of σγ=0.172+0.022−0.032 for the overall sample. This is consistent with and has similar precision to traditional techniques that employ spectroscopic observations to supplement lensing with mass estimates from stellar dynamics. Comparing measurements of γ for individual lenses using both techniques, we find a statistically insignificant correlation of −0.150+0.223−0.217 between the two, indicating a lack of statistical power or deviations from a power-law density in certain lenses. At fixed surface mass density, we measure a redshift dependence, ∂⟨γ⟩/z=0.345+0.322−0.296, that is consistent with traditional techniques for the same sample of Sloan Lens ACS and GALaxy-Lyα EmitteR sYstems (GALLERY) lenses. Interestingly, the consistency breaks down when we measure the dependence of γ on the surface mass density of a lens galaxy. We argue that this is tentative evidence for an inflection point in the total mass-density profile at a few times the galaxy effective radius – breaking the conspiracy
High-performance Coherent Optical Modulators based on Thin-film Lithium Niobate Platform
The coherent transmission technology using digital signal processing and
advanced modulation formats, is bringing networks closer to the theoretical
capacity limit of optical fibres, the Shannon limit. The in-phase quadrature
electro-optic modulator that encodes information on both the amplitude and the
phase of light, is one of the underpinning devices for the coherent
transmission technology. Ideally, such modulator should feature low loss, low
drive voltage, large bandwidth, low chirp and compact footprint. However, these
requirements have been only met on separate occasions. Here, we demonstrate
integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil
these requirements simultaneously. The presented devices exhibit greatly
improved overall performance (half-wave voltage, bandwidth and optical loss)
over traditional lithium niobate counterparts, and support modulation data rate
up to 320 Gbit s-1. Our devices pave new routes for future high-speed,
energy-efficient, and cost-effective communication networks
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