8,099 research outputs found
Observation of Landau quantization and standing waves in HfSiS
Recently, HfSiS was found to be a new type of Dirac semimetal with a line of
Dirac nodes in the band structure. Meanwhile, Rashba-split surface states are
also pronounced in this compound. Here we report a systematic study of HfSiS by
scanning tunneling microscopy/spectroscopy at low temperature and high magnetic
field. The Rashba-split surface states are characterized by measuring Landau
quantization and standing waves, which reveal a quasi-linear dispersive band
structure. First-principles calculations based on density-functional theory are
conducted and compared with the experimental results. Based on these
investigations, the properties of the Rashba-split surface states and their
interplay with defects and collective modes are discussed.Comment: 6 pages, 5 figure
Exact Constructions of a Family of Dense Periodic Packings of Tetrahedra
The determination of the densest packings of regular tetrahedra (one of the
five Platonic solids) is attracting great attention as evidenced by the rapid
pace at which packing records are being broken and the fascinating packing
structures that have emerged. Here we provide the most general analytical
formulation to date to construct dense periodic packings of tetrahedra with
four particles per fundamental cell. This analysis results in six-parameter
family of dense tetrahedron packings that includes as special cases recently
discovered "dimer" packings of tetrahedra, including the densest known packings
with density . This study strongly suggests that
the latter set of packings are the densest among all packings with a
four-particle basis. Whether they are the densest packings of tetrahedra among
all packings is an open question, but we offer remarks about this issue.
Moreover, we describe a procedure that provides estimates of upper bounds on
the maximal density of tetrahedron packings, which could aid in assessing the
packing efficiency of candidate dense packings.Comment: It contains 25 pages, 5 figures
Synthesis of Nitrogen-doped Carbon Nanotubes with Layered Double Hydroxides Containing Iron, Cobalt or Nickel as Catalyst Precursors
Nitrogen-doped carbon nanotubes (CNx) were synthesized by the catalytic chemical vapour deposition of ethylenediamine with layered double hydroxides (LDHs) containing iron, cobalt or nickel as catalyst precursors at 650 °C. The catalytically active metal particles were obtained by calcination of LDHs followed by reduction. X-ray diffraction was used to characterize the structures of the precursors and their calcined products. Transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the grown CNx. The results show that the CNx grown with Mg2Fe-LDH as catalyst precursor have a bamboo-like morphology and large diameter, while hollow tubes are obtained with CoMgAl- andNiMgAl-LDH as catalyst precursors. The CNx grown with CoMgAl-LDH have the highest N-doped content and the CNx grown with NiMgAl-LDH have the highest degree of graphitization among these three products.Keywords: N-doped Carbon Nanotubes, Layered Double Hydroxides, Chemical Vapour Depositio
Approximate perturbed direct homotopy reduction method: infinite series reductions to two perturbed mKdV equations
An approximate perturbed direct homotopy reduction method is proposed and
applied to two perturbed modified Korteweg-de Vries (mKdV) equations with
fourth order dispersion and second order dissipation. The similarity reduction
equations are derived to arbitrary orders. The method is valid not only for
single soliton solution but also for the Painlev\'e II waves and periodic waves
expressed by Jacobi elliptic functions for both fourth order dispersion and
second order dissipation. The method is valid also for strong perturbations.Comment: 8 pages, 1 figur
Effects of Ru Substitution on Dimensionality and Electron Correlations in Ba(Fe_{1-x}Ru_x)_2As_2
We report a systematic angle-resolved photoemission spectroscopy study on
Ba(FeRu)As for a wide range of Ru concentrations (0.15
\emph{x} 0.74). We observed a crossover from two-dimension to
three-dimension for some of the hole-like Fermi surfaces with Ru substitution
and a large reduction in the mass renormalization close to optimal doping.
These results suggest that isovalent Ru substitution has remarkable effects on
the low-energy electron excitations, which are important for the evolution of
superconductivity and antiferromagnetism in this system.Comment: 4 pages, 4 figure
Posh accent and vocal attractiveness in British English
Posh accent in British English is associated with upper class. Previous research on
poshness has been centred on vocabulary, grammar and phonology, but little is
known about the phonetic properties. This study, as part of a larger project, is an
attempt to connect posh accent with attractiveness of voice through a common set of
dimensions originating from emotional prosody research. Using VocalTractLab and
Praat, we created stimuli varying in voice quality, nasality, formant shift ratio, pitch
shift and duration. Results of two separate perception experiments showed that only
voice quality and formant shift ratio functioned significantly. Breathy voice sounded
the most posh and attractive, and pressed voice the least. Likewise, utterances with
the smallest formant shift ratio sounded the most posh and attractive
AtomSim: web-deployed atomistic dynamics simulator
AtomSim, a collection of interfaces for computational crystallography simulations, has been developed. It uses forcefield-based dynamics through physics engines such as the General Utility Lattice Program, and can be integrated into larger computational frameworks such as the Virtual Neutron Facility for processing its dynamics into scattering functions, dynamical functions etc. It is also available as a Google App Engine-hosted web-deployed interface. Examples of a quartz molecular dynamics run and a hafnium dioxide phonon calculation are presented
Genome-wide profiling of uncapped mRNA
Gene transcripts are under extensive posttranscriptional regulation, including the regulation of their
stability. A major route for mRNA degradation produces uncapped mRNAs, which can be generated by
decapping enzymes, endonucleases, and small RNAs. Profiling uncapped mRNA molecules is important for
the understanding of the transcriptome, whose composition is determined by a balance between mRNA
synthesis and degradation. In this chapter, we describe a method to profile these uncapped mRNAs at the
genome scale
Three-dimensional numerical modeling of land subsidence in Shanghai, China
Abstract. Shanghai city has been suffering land subsidence caused by overly exploitation of ground water since 1921, which is a serious problem for this coastal city with altitude of 2.2–4.8 m above mean sea level. The largest cumulative land subsidence amounted to 2.6 m in the downtown area. Measures to decrease the ground water exploitation, change the pumping aquifers, and increase aquifer artificial recharge have been used to mitigate land subsidence since 1961. It is necessary to develop a proper numerical model to simulate and predict land subsidence. In this study, a decoupled three-dimensional (3-D) finite element land subsidence model including a 3-D ground water flow model and a 3-D geo-mechanical model was developed to simulate the 3-D deformation of the aquifer systems in the center area of Shanghai. The area of downtown Shanghai is 660 km2, with 10 million inhabitants, dense high buildings, and 11 metro lines. The simulation spans the period from 1979 to 1995. Two different assumptions have been tested on the side boundary, i.e., precluding the three components of the displacement, or assuming a free-displacement condition. The distribution of calculated land subsidence and horizontal displacements in different aquifers was analyzed. The computed vertical displacement fitted well with the available observations. It has been verified that the two different assumptions on the lateral boundaries in the geo-mechanical model caused different results just limited on nodes close to boundary. The developed 3-D land subsidence model is reasonable and can be used to simulate and predict 3-D movement of aquifer systems in the center area of Shanghai, which could provide scientific support to local government in controlling land subsidence and differential movements of the land surface
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