651 research outputs found
Orbital magnetization and its effects in spin-chiral ferromagnetic Kagome lattice
Recently, Berry phase in the semiclassical dynamical of Bloch electrons has
been found to make a correction to the phase-space density of states and a
general multi-band formula for finite-temperature orbital magnetization has
been given [Phys. Rev. Lett. \textbf{97}, 026603 (2006)], where the orbital
magnetization consists of two parts, i.e., the conventional part
and the Berry-phase correction part . Using this general
formula, we theoretically investigate the orbital magnetization and its effects
on thermoelectric transport and magnetic susceptibility properties of the
two-dimensional \textit{kagom\'{e}} lattice with spin anisotropies included.
The study in this paper is highly interesting by the occurrence of nonzero
Chern number in the lattice. The spin chirality parameter (see text)
results in profound effects on the orbital magnetization properties. It is
found that the two parts in orbital magnetization opposite each other. In
particular, we show that and yield the paramagnetic and
diamagnetic responses, respectively. It is further shown that the orbital
magnetization displays fully different behavior in the metallic and insulating
regions, which is due to the different roles and play in
these two regions. The anomalous Nernst conductivity is also calculated, which
displays a peak-valley structure as a function of the electron Fermi energy.Comment: 9 pages, 7 figure
Atomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study
We study the atomic oxygen adsorption on Pb(111) surface by using
density-functional theory within the generalized gradient approximation and a
supercell approach. The atomic and energetic properties of purely on-surface
and subsurface oxygen structures at the Pb(111) surface are systematically
investigated for a wide range of coverages and adsorption sites. The fcc and
tetra-II sites (see the text for definition) are found to be energetically
preferred for the on-surface and subsurface adsorption, respectively, in the
whole range of coverage considered. The on-surface and subsurface oxygen
binding energies monotonically increase with the coverage, and the latter is
always higher than the former, thus indicating the tendency to the formation of
oxygen islands (clusters) and the higher stability of subsurface adsorption.
The on-surface and subsurface diffusion-path energetics of atomic oxygen, and
the activation barriers for the O penetration from the on-surface to the
subsurface sites are presented at low and high coverages. In particular, it is
shown that the penetration barrier from the on-surface hcp to the subsurface
tetra-I site is as small as 65 meV at low coverage (=0.25). The other
properties of the O/Pb(111) system, including the charge distribution, the
lattice relaxation, the work function, and the electronic density of states,
are also studied and discussed in detail, which consistently show the gradually
stabilizing ionic O-Pb bond with increase of the oxygen coverage.Comment: 31 pages, 16 figure
Transitions from partial to complete generalized synchronizations in bidirectionally coupled chaotic oscillators
Generalized synchronization in an array of mutually (bidirectionally) coupled nonidentical chaotic oscillators is studied. Coupled Lorenz oscillators and coupled Lorenz-Rossler oscillators are adopted as our working models. With increasing the coupling strengths, the system experiences a cascade of transitions from the partial to the global generalized synchronizations, i.e., different oscillators are gradually entrained through a clustering process. This scenario of transitions reveals an intrinsic self-organized order in groups of interacting units, which generalizes the idea of generalized synchronizations in drive-response systems
Strong structural and electronic coupling in metavalent PbS moire superlattices
Moire superlattices are twisted bilayer materials, in which the tunable
interlayer quantum confinement offers access to new physics and novel device
functionalities. Previously, moire superlattices were built exclusively using
materials with weak van der Waals interactions and synthesizing moire
superlattices with strong interlayer chemical bonding was considered to be
impractical. Here using lead sulfide (PbS) as an example, we report a strategy
for synthesizing of moire superlattices coupled by strong chemical bonding. We
use water-soluble ligands as a removable template to obtain free-standing
ultra-thin PbS nanosheets and assemble them into direct-contact bilayers with
various twist angles. Atomic-resolution imaging shows the moire periodic
structural reconstruction at superlattice interface, due to the strong
metavalent coupling. Electron energy loss spectroscopy and theoretical
calculations collectively reveal the twist angle26 dependent electronic
structure, especially the emergent separation of flat bands at small twist
angles. The localized states of flat bands are similar to well-arranged quantum
dots, promising an application in devices. This study opens a new door to the
exploration of deep energy modulations within moire superlattices alternative
to van der Waals twistronics
Determining global mean-first-passage time of random walks on Vicsek fractals using eigenvalues of Laplacian matrices
The family of Vicsek fractals is one of the most important and
frequently-studied regular fractal classes, and it is of considerable interest
to understand the dynamical processes on this treelike fractal family. In this
paper, we investigate discrete random walks on the Vicsek fractals, with the
aim to obtain the exact solutions to the global mean first-passage time
(GMFPT), defined as the average of first-passage time (FPT) between two nodes
over the whole family of fractals. Based on the known connections between FPTs,
effective resistance, and the eigenvalues of graph Laplacian, we determine
implicitly the GMFPT of the Vicsek fractals, which is corroborated by numerical
results. The obtained closed-form solution shows that the GMFPT approximately
grows as a power-law function with system size (number of all nodes), with the
exponent lies between 1 and 2. We then provide both the upper bound and lower
bound for GMFPT of general trees, and show that leading behavior of the upper
bound is the square of system size and the dominating scaling of the lower
bound varies linearly with system size. We also show that the upper bound can
be achieved in linear chains and the lower bound can be reached in star graphs.
This study provides a comprehensive understanding of random walks on the Vicsek
fractals and general treelike networks.Comment: Definitive version accepted for publication in Physical Review
Plant Canopy May Promote Seed Dispersal by Wind
Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s−1), while that of diaspores with low wing loading (0.5 mg mm−2) and terminal velocity (2.5 m s−1) was promoted by relatively high (6 m s−1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community
The Vaccinia Virus (VACV) B1 and Cellular VRK2 Kinases Promote VACV Replication Factory Formation through Phosphorylation-Dependent Inhibition of VACV B12
Comparative examination of viral and host protein homologs reveals novel mechanisms governing downstream signaling effectors of both cellular and vi- ral origin. The vaccinia virus B1 protein kinase is involved in promoting multiple facets of the virus life cycle and is a homolog of three conserved cellular enzymes called vaccinia virus-related kinases (VRKs). Recent evidence indicates that B1 and VRK2 mediate a com- mon pathway that is largely uncharacterized but appears independent of previous VRK substrates. Interestingly, separate studies described a novel role for B1 in inhibiting vac- cinia virus protein B12, which otherwise impedes an early event in the viral lifecycle. Herein, we characterize the B1/VRK2 signaling axis to better understand their shared functions. First, we demonstrate that vaccinia virus uniquely requires VRK2 for viral repli- cation in the absence of B1, unlike other DNA viruses. Employing loss-of-function analy- sis, we demonstrate that vaccinia virus’s dependence on VRK2 is only observed in the presence of B12, suggesting that B1 and VRK2 share a pathway controlling B12. More- over, we substantiate a B1/VRK2/B12 signaling axis by examining coprecipitation of B12 by B1 and VRK2. Employing execution point analysis, we reveal that virus replication proceeds normally through early protein translation and uncoating but stalls at replica- tion factory formation in the presence of B12 activity. Finally, structure/function analyses of B1 and VRK2 demonstrate that enzymatic activity is essential for B1 or VRK2 to inhibit B12. Together, these data provide novel insights into B1/VRK signaling coregulation and support a model in which these enzymes modulate B12 in a phosphorylation-depen- dent manner
Different forms of TFIIH for transcription and DNA repair: Holo-TFIIH and a nucleotide excision repairosome
AbstractYeast TFIIH that is active in transcription can be dissociated into three components: a 5-subunit core, the SSL2 gene product, and a complex of 47 kDa, 45 kDa, and 33 kDa polypeptides that possesses protein kinase activity directed towards the C-terminal repeat domain of RNA polymerase II. These three components can reconstitute fully functional TFIIH, and all three are required for transcription in vitro. By contrast, TFIIH that is highly active in nucleotide excision repair (NER) lacks the kinase complex and instead contains the products of all other genes known to be required for NER in yeast: RAD1, RAD2, RAD4, RAD10, and RAD14. This repairosome is not active in reconstituted transcription in vitro and is significantly more active than any of the constituent polypeptides in correcting defective repair in extracts from strains mutated in NER genes
- …