Properties of Steady Sub-Alfv\'enic Solar Wind in Comparison with Super-Alfv\'enic Wind from Measurements of Parker Solar Probe

We identify more than ten steady sub-Alfv\'enic solar wind intervals from the measurements of the Parker Solar Probe (PSP) from encounter 8 to encounter 14. An analysis of these sub-Alfv\'enic intervals reveals similar properties and similar origins. In situ measurements show that these intervals feature a decreased radial Alfv\'en Mach number resulting from a reduced density and a relatively low velocity, and that switchbacks are suppressed in these intervals. Magnetic source tracing indicates that these sub-Alfv\'enic streams generally originate from the boundaries inside coronal holes, or narrow/small regions of open magnetic fields. Such properties and origins suggest that these streams are low Mach-number boundary layers (LMBLs), which is a special component of the pristine solar wind proposed by Liu et al. We find that the LMBL wind, the fast wind from deep inside coronal holes, and the slow streamer wind constitute three typical components of the young solar wind near the Sun. In these sub-Alfv\'enic intervals, the Alfv\'en radius varies between 15 and 25 solar radii, in contrast with a typical 12 radii for the Alfv\'en radius of the super-Alfv\'enic wind. These results give a self-consistent picture interpreting the PSP measurements in the vicinity of the Sun.Comment: Accepted for publication in Ap

Intrinsically Interacting Higher-Order Topological Superconductors

We propose a minimal interacting lattice model for two-dimensional class-D higher-order topological superconductors with no free-fermion realization. A Lieb-Schultz-Mattis-type constraint has been proposed and applied to guide our lattice model construction. Our model exhibits a trivial product ground state in the weakly interacting regime while increasing electron correlations provoke a novel topological quantum phase transition to a $D_4$-symmetric higher-order topological superconducting state. The symmetry-protected Majorana corner modes are numerically confirmed with the matrix-product-state technique. Our theory paves the way for studying correlated higher-order topology with explicit lattice model constructions.Comment: 11 pages, 6 figure

Modeling and analysis of hydraulic fracture complexity index in sandy conglomerate reservoirs based on genetic expression programming—A case study in Xinjiang Oilfield

The stimulation effect of oil wells is seriously affected by the complexity of hydraulic fractures, and the analysis of the factors that control the fracture complexity index has become the key to fracturing design in sandy conglomerate reservoirs. Based on the intrinsic relationship between geological engineering parameters and the fractures complexity index, a Genetic Expression Programming (GEP) method, which has broad advantages in solving multi-factor nonlinear fitting and black-box prediction problems, is proposed to analyze the hydraulic fracture complexity index. Combined with the geoengineering factors that affect the hydraulic fractures propagation, a comprehensive index calculation method is established to analyze the relative importance of these features and 18 reconstructed features were obtained by collecting the geoengineering parameter data of 118 fracturing sections in 8 fracturing wells in Jinlong oilfield. The principal component analysis was performed to eliminate the interaction between the features, and then a GEP-based fractures complexity index calculation model was developed. The partial dependence plot is used to analyze the influence of the main control feature (variable) on the hydraulic fracture complexity index. It showed that GEP model can achieve satisfactory performance (Training set: R = 0.861; Test set: R = 0.817) by statistical parameters. The results showed that the model can calculate the hydraulic fracture complexity index quickly and precisely. The influence of geological engineering control factors can be obtained. It proved that the GEP method can effectively analyze and evaluate the complexity in sandy conglomerate reservoirs

Enhanced Thermoelectric Power in Dual-Gated Bilayer Graphene

Thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a band-gap by applying a perpendicular electric field on bilayer graphene. We uncover a large enhancement in thermoelectric power at low temperature, which may open up a new possibility in low temperature thermoelectric application using graphene-based device.Comment: 12 pages, 4 figure

Discovery of a Novel Prolactin in Non-Mammalian Vertebrates: Evolutionary Perspectives and Its Involvement in Teleost Retina Development

BACKGROUND:The three pituitary hormones, viz. prolactin (PRL), growth hormone (GH) and somatolactin (SL), together with the mammalian placental lactogen (PL), constitute a gene family of hormones with similar gene structure and encoded protein sequences. These hormones are believed to have evolved from a common ancestral gene through several rounds of gene duplication and subsequent divergence. PRINCIPAL FINDINGS:In this study, we have identified a new PRL-like gene in non-mammalian vertebrates through bioinformatics and molecular cloning means. Phylogenetic analyses showed that this novel protein is homologous to the previously identified PRL. A receptor transactivation assay further showed that this novel protein could bind to PRL receptor to trigger the downstream post-receptor event, indicating that it is biologically active. In view of its close phylogenetic relationship with PRL and also its ability to activate PRL receptor, we name it as PRL2 and the previously identified PRL as PRL1. All the newly discovered PRL2 sequences possess three conserved disulfide linkages with the exception of the shark PRL2 which has only two. In sharp contrast to the classical PRL1 which is predominantly expressed in the pituitary, PRL2 was found to be mainly expressed in the eye and brain of the zebrafish but not in the pituitary. A largely reduced inner nuclear layer of the retina was observed after morpholino knockdown of zebrafish PRL2, indicating its role on retina development in teleost. SIGNIFICANCE:The discovery of this novel PRL has revitalized our understanding on the evolution of the GH/PRL/SL/PL gene family. Its unique expression and functions in the zebrafish eye also provide a new avenue of research on the neuroendocrine control of retina development in vertebrates