In quantum field theory, Lorentz invariance leads to three types of fermion-Dirac, Weyl and Majorana. Although the existence of Weyl and Majorana fermions as elementary particles in high-energy ...physics is debated, all three types of fermion have been proposed to exist as low-energy, long-wavelength quasiparticle excitations in condensed-matter systems. The existence of Dirac and Weyl fermions in condensed-matter systems has been confirmed experimentally, and that of Majorana fermions is supported by various experiments. However, in condensed-matter systems, fermions in crystals are constrained by the symmetries of the 230 crystal space groups rather than by Lorentz invariance, giving rise to the possibility of finding other types of fermionic excitation that have no counterparts in high-energy physics. Here we use angle-resolved photoemission spectroscopy to demonstrate the existence of a triply degenerate point in the electronic structure of crystalline molybdenum phosphide. Quasiparticle excitations near a triply degenerate point are three-component fermions, beyond the conventional Dirac-Weyl-Majorana classification, which attributes Dirac and Weyl fermions to four- and two-fold degenerate points, respectively. We also observe pairs of Weyl points in the bulk electronic structure of the crystal that coexist with the three-component fermions. This material thus represents a platform for studying the interplay between different types of fermions. Our experimental discovery opens up a way of exploring the new physics of unconventional fermions in condensed-matter systems.
Conventional metals become harder with decreasing grain sizes, following the classical Hall-Petch relationship. However, this relationship fails and softening occurs at some grain sizes in the ...nanometer regime for some alloys. In this study, we discovered that plastic deformation mechanism of extremely fine nanograined metals and their hardness are adjustable through tailoring grain boundary (GB) stability. The electrodeposited nanograined nickel-molybdenum (Ni–Mo) samples become softened for grain sizes below 10 nanometers because of GB-mediated processes. With GB stabilization through relaxation and Mo segregation, ultrahigh hardness is achieved in the nanograined samples with a plastic deformation mechanism dominated by generation of extended partial dislocations. Grain boundary stability provides an alternative dimension, in addition to grain size, for producing novel nanograined metals with extraordinary properties.
Noncoding RNAs (ncRNAs) play increasingly appreciated gene-regulatory roles. Here, we describe a regulatory network centered on four ncRNAs—a long ncRNA, a circular RNA, and two microRNAs—using gene ...editing in mice to probe the molecular consequences of disrupting key components of this network. The long ncRNA Cyrano uses an extensively paired site to miR-7 to trigger destruction of this microRNA. Cyrano-directed miR-7 degradation is much more effective than previously described examples of target-directed microRNA degradation, which come primarily from studies of artificial and viral RNAs. By reducing miR-7 levels, Cyrano prevents repression of miR-7–targeted mRNAs and enables accumulation of Cdr1as, a circular RNA known to regulate neuronal activity. Without Cyrano, excess miR-7 causes cytoplasmic destruction of Cdr1as in neurons, in part through enhanced slicing of Cdr1as by a second miRNA, miR-671. Thus, several types of ncRNAs can collaborate to establish a sophisticated regulatory network.
Display omitted
•A long noncoding RNA, a circular RNA, and two microRNAs form a regulatory network•The Cyrano long noncoding RNA directs potent, multiple-turnover destruction of miR-7•Unchecked miR-7 prevents accumulation of Cdr1as circular RNA in cytoplasm of neurons•miR-7 prevents this accumulation by enhancing the miR-671–directed slicing of Cdr1as
Three different classes of noncoding RNA converge in a regulatory network whereby a long noncoding RNA represses a microRNA via target-directed microRNA degradation, which in turn enables the accumulation of a circular RNA in the mouse brain.
Topological semimetals are characterized by symmetry-protected band crossings, which can be preserved in different dimensions in momentum space, forming zero-dimensional nodal points, one-dimensional ...nodal lines, or even two-dimensional nodal surfaces. Materials harboring nodal points and nodal lines have been experimentally verified, whereas experimental evidence of nodal surfaces is still lacking. Here, using angle-resolved photoemission spectroscopy (ARPES), we reveal the coexistence of Dirac nodal surfaces and nodal lines in the bulk electronic structures of ZrSiS. As compared with previous ARPES studies on ZrSiS, we obtained pure bulk states, which enable us to extract unambiguously intrinsic information of the bulk nodal surfaces and nodal lines. Our results show that the nodal lines are the only feature near the Fermi level and constitute the whole Fermi surfaces. We not only prove that the low-energy quasiparticles in ZrSiS are contributed entirely by Dirac fermions but also experimentally realize the nodal surface in topological semimetals.
2019 novel coronavirus (2019-nCoV) infection has been spreading in China since December 2019. Neonates are presumably the high-risk population susceptible to 2019-nCoV due to immature immune ...function. The neonatal intensive care unit (NICU) should be prepared for 2019-nCoV infections as far as possible. The emergency response plan enables the efficient response capability of NICU. During the epidemic of 2019-nCoV, the emergency response plan for the NICU should be based on the actual situation, including diagnosis, isolation, and treatment, as well as available equipment and staffing, and take into account the psychosocial needs of the families and neonatal care staff.
In this randomized trial involving infertile women with the polycystic ovary syndrome, frozen-embryo transfer was associated with a higher rate of live birth than was fresh-embryo transfer after the ...first transfer.
In vitro fertilization (IVF) is widely performed as an infertility treatment and has resulted in the births of more than 5 million infants worldwide.
1
However, there are concerns about the safety of the procedures for women and for their infants.
1
,
2
The ovarian hyperstimulation syndrome (which is caused by ovarian enlargement, an increase in vascular permeability and abdominal ascites, and intravascular hemoconcentration) is a potentially life-threatening complication of ovarian stimulation.
3
Pregnancies conceived by means of IVF are associated with greater risks of maternal and neonatal complications, including preeclampsia, preterm delivery, low birth weight, and congenital anomalies, than are spontaneous pregnancies. . . .
PDF
