1,439 research outputs found
Changes of the Wetland Landscape and the Consequent Impacts on the Waterbirds in Western Songnen Plain
AbstractWetland have been shrinking rapidly in area and degrading in functioning. These all hold back the sustainable development of human communities and caused globe changes. Taken Western Songnen Plain as a case study, a series of landscape pattern metrics were selectively used to quantify the wetland changes. The correlation between the acreage losses of wetland and the number of waterbirds was studied based on the statistical data of waterbirds. The results showed that the wetlands had undergone substantial loss in area and fragmented during the nearly 50 years in the study area. The changes of the wetlands exerted impacts on the waterbirds which depend on the wetlands. The waterbirds changed in two ways: Waterbirds dropped rapidly in number at the first stage, then come down gently. Secondly, waterbirds declined gently in number at the first time period, then dropped rapidly. From the study, we concluded that wetlands had been shrinking in area and fragmented and partly accounted for decline and even extinctions of waterbirds during the nearly 50 years during the study period
Constraints on primordial curvature power spectrum with pulsar timing arrays
The stochastic signal detected by NANOGrav, PPTA, EPTA, and CPTA can be
explained by the scalar-induced gravitational waves. In order to determine the
scalar-induced gravitational waves model that best fits the stochastic signal,
we employ both single- and double-peak parameterizations for the power spectrum
of the primordial curvature perturbations, where the single-peak scenarios
include the -function, box, lognormal, and broken power law model, and
the double-peak scenario is described by the double lognormal form. Using
Bayesian inference, we find that there is no significant evidence for or
against the single-peak scenario over the double-peak model, with (Bayes
factors) among these models . Therefore, we are not able
to distinguish the different shapes of the power spectrum of the primordial
curvature perturbation with the current sensitivity of pulsar timing arrays.Comment: 19 pages, 1 table, 7 figure
Preselection of QTL markers enhances accuracy of genomic selection in Norway spruce
Genomic prediction (GP) or genomic selection is a method to predict the accumulative effect of all quantitative trait loci (QTLs) in a population by estimating the realized genomic relationships between the individuals and by capturing the linkage disequilibrium between markers and QTLs. Thus, marker preselection is considered a promising method to capture Mendelian segregation effects. Using QTLs detected in a genome-wide association study (GWAS) may improve GP. Here, we performed GWAS and GP in a population with 904 clones from 32 full-sib families using a newly developed 50 k SNP Norway spruce array. Through GWAS we identified 41 SNPs associated with budburst stage (BB) and the largest effect association explained 5.1% of the phenotypic variation (PVE). For the other five traits such as growth and wood quality traits, only 2 - 13 associations were observed and the PVE of the strongest effects ranged from 1.2% to 2.0%. GP using approximately 100 preselected SNPs, based on the smallest p-values from GWAS showed the greatest predictive ability (PA) for the trait BB. For the other traits, a preselection of 2000-4000 SNPs, was found to offer the best model fit according to the Akaike information criterion being minimized. But PA-magnitudes from GP using such selections were still similar to that of GP using all markers. Analyses on both real-life and simulated data also showed that the inclusion of a large QTL SNP in the model as a fixed effect could improve PA and accuracy of GP provided that the PVE of the QTL was >= 2.5%
Constraining the Merger History of Primordial-Black-Hole Binaries from GWTC-3
Primordial black holes (PBHs) can be not only cold dark matter candidates but
also progenitors of binary black holes observed by LIGO-Virgo-KAGRA (LVK)
Collaboration. The PBH mass can be shifted to the heavy distribution if
multi-merger processes occur. In this work, we constrain the merger history of
PBH binaries using the gravitational wave events from the third
Gravitational-Wave Transient Catalog (GWTC-3). Considering four commonly used
PBH mass functions, namely the log-normal, power-law, broken power-law, and
critical collapse forms, we find that the multi-merger processes make a
subdominant contribution to the total merger rate. Therefore, the effect of
merger history can be safely ignored when estimating the merger rate of PBH
binaries. We also find that GWTC-3 is best fitted by the log-normal form among
the four PBH mass functions and confirm that the stellar-mass PBHs cannot
dominate cold dark matter.Comment: 11 pages, 8 figures, 2 tables; accepted for publication in PR
Quantized charge-pumping in higher-order topological insulators
We study the quantized charge pumping of higher-order topological insulators
(HOTIs) with edge-corner correspondences based on the combination of the
rotation of in-plane magnetic field and the quantum spin Hall effect. A picture
of a specific charge pumping process is uncovered with the help of the
non-equilibrium Green's function method. Significantly, we demonstrate that the
quantized charge pumping current is achieved without the participation of bulk
states, and the charges move along the boundary of the sample. Furthermore, the
effects of external parameters on the pumping current is also studied. We find
that the magnitude and direction of the pumping current can be manipulated by
adjusting the coupling strength between the leads and sample. Our work deepens
the understanding of the charge pumping in HOTIs and extends the study of their
transport properties.Comment: 8 pages, 5 figure
Robust Finite-Time Control for Spacecraft with Coupled Translation and Attitude Dynamics
Robust finite-time control for spacecraft with coupled translation and attitude dynamics is investigated in the paper. An error-based spacecraft motion model in six-degree-of-freedom is firstly developed. Then a finite-time controller based on nonsingular terminal sliding mode control technique is proposed to achieve translation and attitude maneuvers in the presence of model uncertainties and environmental perturbations. A finite-time observer is designed and a modified controller is then proposed to deal with uncertainties and perturbations and alleviate chattering. Numerical simulations are finally provided to illustrate the performance of the proposed controllers
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