3,672 research outputs found
21 cm foreground removal using AI and frequency-difference technique
The deep learning technique has been employed in removing foreground
contaminants from 21 cm intensity mapping, but its effectiveness is limited by
the large dynamic range of the foreground amplitude. In this study, we develop
a novel foreground removal technique grounded in U-Net networks. The essence of
this technique lies in introducing an innovative data preprocessing step
specifically, utilizing the temperature difference between neighboring
frequency bands as input, which can substantially reduce the dynamic range of
foreground amplitudes by approximately two orders of magnitude. This reduction
proves to be highly advantageous for the U-Net foreground removal. We observe
that the HI signal can be reliably recovered, as indicated by the
cross-correlation power spectra showing unity agreement at the scale of Mpc in the absence of instrumental effects. Moreover, accounting for
the systematic beam effects, our reconstruction displays consistent
auto-correlation and cross-correlation power spectrum ratios at the
level across scales Mpc, with only a 10% reduction
observed in the cross-correlation power spectrum at Mpc. The
effects of redshift-space distortion are also reconstructed successfully, as
evidenced by the quadrupole power spectra matching. In comparison, our method
outperforms the traditional Principal Component Analysis method, which derived
cross-correlation ratios are underestimated by around 75%. We simulated various
white noise levels in the map and found that the mean cross-correlation ratio
when the level of the thermal noise is
smaller than or equal to that of the HI signal. We conclude that the proposed
frequency-difference technique can significantly enhance network performance by
reducing the amplitude range of foregrounds and aiding in the prevention of HI
loss.Comment: 18 pages, 16 figure
Chromosomal DNA deletion confers phage resistance to Pseudomonas aeruginosa.
Bacteria develop a broad range of phage resistance mechanisms, such as prevention of phage adsorption and CRISPR/Cas system, to survive phage predation. In this study, Pseudomonas aeruginosa PA1 strain was infected with lytic phage PaP1, and phage-resistant mutants were selected. A high percentage (~30%) of these mutants displayed red pigmentation phenotype (Red mutant). Through comparative genomic analysis, one Red mutant PA1r was found to have a 219.6 kb genomic fragment deletion, which contains two key genes hmgA and galU related to the observed phenotypes. Deletion of hmgA resulted in the accumulation of a red compound homogentisic acid; while A galU mutant is devoid of O-antigen, which is required for phage adsorption. Intriguingly, while the loss of galU conferred phage resistance, it significantly attenuated PA1r in a mouse infection experiment. Our study revealed a novel phage resistance mechanism via chromosomal DNA deletion in P. aeruginosa
Effects of In Vitro Maturation on Histone Acetylation in Metaphase II Oocytes and Early Cleavage Embryos
In vitro maturation (IVM) of oocyte is an effective procedure for avoiding ovarian hyperstimulation syndrome in patients with polycystic ovaries (PCOS) during in vitro fertilization (IVF). To investigate the influences of IVM on epigenetic reprogramming and to search for the possible reasons for the lower rates of fertilization and cleavage in IVM oocytes, we examined the expression of two enzymes controlling histone acetylation, histone acetyltransferase GCN5 (GCN5) and histone deacetylase 1 (HDAC1), as well as their common target, acetyl-histone H3 (Ac-H3), in mouse metaphase II (MII) oocytes and preimplantation embryos. Results showed that IVM downregulated the protein expression of GCN5 in MII oocytes and two-cell embryos and changed the distribution of GCN5 in two-cell embryos. Expression of HDAC1 mRNA in MII oocytes and two-cell embryos decreased in the IVM group. However, none of these changes persisted after two-cell embryos. Levels of Ac-H3 in both oocytes and embryos remained unchanged after IVM. Our studies indicated that IVM could affect the protein and gene expression related to histone acetylation in oocytes and early cleavage embryos. By function of selection, parts of the changes could be recovered in late embryo development
Probiotic Therapy for Treating Behavioral and Gastrointestinal Symptoms in Autism Spectrum Disorder: A Systematic Review of Clinical Trials
The therapeutic potentials of probiotics in autism spectrum disorder (ASD) remains controversial, with the only existing systematic review on this topic published in 2015. Results from new trials have become available in recent years. We therefore conducted an updated systematic review, to assess the efficacy of probiotics in relieving behavioral symptoms of ASD and gastrointestinal comorbidities. Our review includes two randomized controlled trials, which showed improvement of ASD behaviors, and three open trials, all which exhibited a trend of improvement. Four of these trials concluded from subjective measures that gastrointestinal function indices showed a trend of improvement with probiotic therapy. Additional rigorous trials are needed to evaluate the effects of probiotic supplements in ASD
Magnetic-coupled electronic landscape in bilayer-distorted titanium-based kagome metals
Quantum materials whose atoms are arranged on a lattice of corner-sharing
triangles, , the kagome lattice, have recently emerged as a
captivating platform for investigating exotic correlated and topological
electronic phenomena. Here, we combine ultra-low temperature angle-resolved
photoemission spectroscopy (ARPES) with scanning tunneling microscopy and
density functional theory calculations to reveal the fascinating electronic
structure of the bilayer-distorted kagome material
TiBi, where stands for Nd and Yb.
Distinct from other kagome materials, TiBi exhibits
two-fold, rather than six-fold, symmetries, stemming from the distorted kagome
lattice, which leads to a unique electronic structure. Combining experiment and
theory we map out the electronic structure and discover double flat bands as
well as multiple van Hove singularities (VHSs), with one VHS exhibiting
higher-order characteristics near the Fermi level. Notably, in the magnetic
version NdTiBi, the ultra-low base temperature ARPES measurements
unveil an unconventional band splitting in the band dispersions which is
induced by the ferromagnetic ordering. These findings reveal the potential of
bilayer-distorted kagome metals TiBi as a promising
platform for exploring novel emergent phases of matter at the intersection of
strong correlation and magnetism
Non-trivial band topology and orbital-selective electronic nematicity in a new titanium-based kagome superconductor
Electronic nematicity that spontaneously breaks rotational symmetry has been
shown as a generic phenomenon in correlated quantum systems including
high-temperature superconductors and the AV3Sb5 (A = K, Rb, Cs) family with a
kagome network. Identifying the driving force has been a central challenge for
understanding nematicity. In iron-based superconductors, the problem is
complicated because the spin, orbital and lattice degrees of freedom are
intimately coupled. In vanadium-based kagome superconductors AV3Sb5, the
electronic nematicity exhibits an intriguing entanglement with the charge
density wave order (CDW), making understanding its origin difficult. Recently,
a new family of titanium-based kagome superconductors ATi3Bi5 has been
synthesized. In sharp contrast to its vanadium-based counterpart, the
electronic nematicity occurs in the absence of CDW. ATi3Bi5 provides a new
window to explore the mechanism of electronic nematicity and its interplay with
the orbital degree of freedom. Here, we combine polarization-dependent
angle-resolved photoemission spectroscopy with density functional theory to
directly reveal the band topology and orbital characters of the multi-orbital
RbTi3Bi5. The promising coexistence of flat bands, type-II Dirac nodal line and
nontrivial Z2 topological states is identified in RbTi3Bi5. Remarkably, our
study clearly unveils the orbital character change along the G-M and G-K
directions, implying a strong intrinsic inter-orbital coupling in the Ti-based
kagome metals, reminiscent of iron-based superconductors. Furthermore,
doping-dependent measurements directly uncover the orbital-selective features
in the kagome bands, which can be well explained by the d-p hybridization. The
suggested d-p hybridization, in collaboration with the inter-orbital coupling,
could account for the electronic nematicity in ATi3Bi5
- …