3,080 research outputs found
Topological quantum phase transition in an S=2 spin chain
We construct a model Hamiltonian for S = 2 spin chain, where a variable
parameter is introduced. The edge spin is S = 1 for , and
S = 3/2 for . Due to the topological distinction of the edge
states, these two phases must be separated by one or several topological
quantum phase transitions. We investigate the nature of the quantum phase
transition by DMRG calculation, and propose a phase diagram for this model.Comment: 5 pages, 4 figure
Bifurcations of limit cycles from quintic Hamiltonian systems with a double figure eight loop☆☆The work was supported in part by Australia Research Counsil under the Discovery Projects scheme (grant ID: DP0559111).
AbstractThis paper deals with Liénard equations of the form x˙=y, y˙=P(x)+yQ(x,y), with P and Q polynomials of degree 5 and 4 respectively. Attention goes to perturbations of the Hamiltonian vector fields with an elliptic Hamiltonian of degree six, exhibiting a double figure eight loop. The number of limit cycles and their distributions are given by using the methods of bifurcation theory and qualitative analysis
Constraining Neutrino Cosmologies with Nonlinear Reconstruction
Nonlinear gravitational evolution induces strong nonlinearities in the
observed cosmological density fields, leading to positive off-diagonal
correlations in the power spectrum covariance. This has caused the information
saturation in the power spectrum, e.g., the neutrino mass constraints from the
nonlinear power spectra are lower than their linear counterparts by a factor of
at . In this paper, we explore how nonlinear reconstruction
methods improve the cosmological information from nonlinear cosmic fields. By
applying nonlinear reconstruction to cold dark matter fields from the Quijote
simulations, we find that nonlinear reconstruction can improve the constraints
on cosmological parameters significantly, nearly reaching the linear theory
limit. For neutrino mass, the result is only lower than the linear power
spectrum, i.e., the theoretical best result. This makes nonlinear
reconstruction an efficient and useful method to extract neutrino information
from current and upcoming galaxy surveys.Comment: 14 pages, 8 figures, accepted versio
Effects of transgenic Cry1Ac + CpTI cotton on non-target mealybug pest Ferrisia virgata and its predator Cryptolaemus montrouzieri
Recently, several invasive mealybugs (Hemiptera: Pseudococcidae) have rapidly spread to Asia and have become a serious threat to the production of cotton including transgenic cotton. Thus far, studies have mainly focused on the effects of mealybugs on non-transgenic cotton, without fully considering their effects on transgenic cotton and trophic interactions. Therefore, investigating the potential effects of mealybugs on transgenic cotton and their key natural enemies is vitally important. A first study on the effects of transgenic cotton on a non-target mealybug, Ferrisia virgata (Cockerell) (Hemiptera: Pseudococcidae) was performed by comparing its development, survival and body weight on transgenic cotton leaves expressing Cry1Ac (Bt toxin) + CpTI (Cowpea Trypsin Inhibitor) with those on its near-isogenic non-transgenic line. Furthermore, the development, survival, body weight, fecundity, adult longevity and feeding preference of the mealybug predator Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) was assessed when fed F. virgata maintained on transgenic cotton. In order to investigate potential transfer of Cry1Ac and CpTI proteins via the food chain, protein levels in cotton leaves, mealybugs and ladybirds were quantified. Experimental results showed that F. virgata could infest this bivalent transgenic cotton. No significant differences were observed in the physiological parameters of the predator C. montrouzieri offered F. virgata reared on transgenic cotton or its near-isogenic line. Cry1Ac and CpTI proteins were detected in transgenic cotton leaves, but no detectable levels of both proteins were present in the mealybug or its predator when reared on transgenic cotton leaves. Our bioassays indicated that transgenic cotton poses a negligible risk to the predatory coccinellid C. montrouzieri via its prey, the mealybug F.virgata
9,9-Dimethyl-12-phenyl-8,9-dihydro-12H-benzo[a]xanthen-11(10H)-one
The title compound, C25H22O2, was synthesized via the three-component coupling of benzaldehyde, 2-naphthol and 5,5-dimethylÂcycloÂhexane-1,3-dione. In the crystal structure, centrosymmetrically related molÂecules are linked into dimers by pairs of interÂmolecular C—H⋯O hydrogen bonds. The dimers are further connected into a three-dimensional network by π–π aromatic stacking interÂactions involving the naphthalene ring system, with centroid–centroid separations of 3.695 (7) Å
Cross-linked CoMoO4/rGO nanosheets as oxygen reduction catalyst
Development of inexpensive and robust electrocatalysts towards oxygen reduction reaction
(ORR) is crucial for the cost-affordable manufacturing of metal-air batteries and fuel cells. Here
we show that cross-linked CoMoO4 nanosheets and reduced graphene oxide (CoMoO4/rGO) can
be integrated in a hybrid material under one-pot hydrothermal conditions, yielding a composite
material with promising catalytic activity for oxygen reduction reaction (ORR). Cyclic voltammetry
(CV) and linear sweep voltammetry (LSV) were used to investigate the efficiency of the fabricated
CoMoO4/rGO catalyst towards ORR in alkaline conditions. The CoMoO4/rGO composite revealed
the main reduction peak and onset potential centered at 0.78 and 0.89 V (vs. RHE), respectively.
This study shows that the CoMoO4/rGO composite is a highly promising catalyst for the ORR under
alkaline conditions, and potential noble metal replacement cathode in fuel cells and metal-air batteries
Skyrmion Lattice in Two-Dimensional Chiral Magnet
We develop a theory of the magnetic field-induced formation of Skyrmion
crystal state in chiral magnets in two spatial dimensions, motivated by the
recent discovery of the Skyrmionic phase of magnetization in thin film of
FeCoSi and in the A-phase of MnSi. Ginzburg-Landau functional
of the chiral magnet re-written in the CP representation is shown to be a
convenient framework for the analysis of the Skyrmion states. Phase diagram of
the model at zero temperature gives a sequence of ground states, helical spin
Skyrme crystal ferromagnet, as the external field
increases, in good accord with the thin-film experiment. In close analogy
with Abrikosov's derivation of the vortex lattice solution in type-II
superconductor, the CP mean-field equation is solved and shown to reproduce
the Skyrmion crystal state.Comment: 10 pages, 7 figure
Numerical simulation for machining S-tube by abrasive flow with various particle volume fractions
Abrasive flow machining has become an economical and efficient ultra-precision process for machining complex-shaped pipe parts, and processing effect is exceedingly subject to particle volume fraction. In this paper, aiming at uncovering the influence of various particle volume fractions on the machining result of abrasive flow finishing, based on fluid mechanics theory, mixed phase model and discrete phase model were conducted, FLUENT software was resorted to simulate the numerical characteristics of the solid-liquid two-phase flow field in the inner channel of S-tube with different-particle-volume-fraction abrasive flows, the mechanism of erosion and wear of particles was uncovered, which provides a theoretical basis for abrasive flow machining S-tube structured components
4-Benzyl-4-methylÂmorpholinium hexaÂfluoroÂphosphate
In the title compound, C12H18NO+·PF6
−, the asymmetric unit consists of two cation–anion pairs. The six F atoms of one anion are disordered over two sets of sites in a 0.592 (6):0.408 (6) ratio. The morpholinium rings adopt chair conformations
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