1,956 research outputs found
The finite-width Laplace sum rules for scalar glueball in instanton liquid model
In the framework of a semi-classical expansion for quantum chromodynamics in
the instanton liquid background, the correlation function of the
scalar glueball current is given. Besides the pure classical and quantum
contributions, the contributions arising from the interactions between the
classical instanton fields and quantum gluons are taken into account as well.
Instead of the usual zero-width approximation for the resonance, the
Brite-Wigner form for the spectral function of the finite-width resonance is
adopted. The family of the Laplace sum rules for the scalar glueball in quantum
chromodynamics with and without light quarks are studed. A consistency between
the subtracted and unsubtracted sum rules are very well justified, and the
values of the mass, decay width, and the coupling to the corresponding current
for the resonance in which the glueball fraction is dominant, are
obtained.Comment: 6 figure
Self-assembly of Nanometer-scale Magnetic Dots with Narrow Size Distributions on an Insulating Substrate
The self-assembly of iron dots on the insulating surface of NaCl(001) is
investigated experimentally and theoretically. Under proper growth conditions,
nanometer-scale magnetic iron dots with remarkably narrow size distributions
can be achieved in the absence of a wetting layer Furthermore, both the
vertical and lateral sizes of the dots can be tuned with the iron dosage
without introducing apparent size broadening, even though the clustering is
clearly in the strong coarsening regime. These observations are interpreted
using a phenomenological mean-field theory, in which a coverage-dependent
optimal dot size is selected by strain-mediated dot-dot interactions.Comment: 5 pages, 4 figure
Atomic structure, energetics, and dynamics of topological solitons in Indium chains on Si(111) surfaces
Based on scanning tunneling microscopy and first-principles theoretical
studies, we characterize the precise atomic structure of a topological soliton
in In chains grown on Si(111) surfaces. Variable-temperature measurements of
the soliton population allow us to determine the soliton formation energy to be
~60 meV, smaller than one half of the band gap of ~200 meV. Once created, these
solitons have very low mobility, even though the activation energy is only
about 20 meV; the sluggish nature is attributed to the exceptionally low
attempt frequency for soliton migration. We further demonstrate local electric
field-enhanced soliton dynamics.Comment: 5 pages, 3 figure
Half-Heusler Compounds as a New Class of Three-Dimensional Topological Insulators
Using first-principles calculations within density functional theory, we
explore the feasibility of converting ternary half-Heusler compounds into a new
class of three-dimensional topological insulators (3DTI). We demonstrate that
the electronic structure of unstrained LaPtBi as a prototype system exhibits
distinct band-inversion feature. The 3DTI phase is realized by applying a
uniaxial strain along the [001] direction, which opens a bandgap while
preserving the inverted band order. A definitive proof of the strained LaPtBi
as a 3DTI is provided by directly calculating the topological Z2 invariants in
systems without inversion symmetry. We discuss the implications of the present
study to other half-Heusler compounds as 3DTI, which, together with the
magnetic and superconducting properties of these materials, may provide a rich
platform for novel quantum phenomena.Comment: 4 pages, 5 figures; Phys. Rev. Lett. (in press
Direct extraction of the Eliashberg function for electron-phonon coupling: A case study of Be(1010)
We propose a systematic procedure to directly extract the Eliashberg function
for electron-phonon coupling from high-resolution angle-resolved photoemission
data. The procedure is successfully applied to the Be(1010) surface, providing
new insights to electron-phonon coupling at this surface. The method is shown
to be robust against imperfections in experimental data and suitable for wider
applications.Comment: 4 pages, 4 figures. More details concerning the procedure are
include
Stacking Principle and Magic Sizes of Transition Metal Nanoclusters Based on Generalized Wulff Construction
Nanoclusters with extra stability at certain cluster sizes are known as magic clusters with exotic properties. The classic Wulff construction principle, which stipulates that the preferred structure of a cluster should minimize its total surface energy, is often invoked in determining the cluster magicity, resulting in close-shelled Mackay icosahedronal clusters with odd-numbered magic sizes of 13, 55, 147, etc. Here we use transition metal clusters around size 55 as prototypical examples to demonstrate that, in the nanometer regime, the classic Wulff construction principle needs to be generalized to primarily emphasize the edge atom effect instead of the surface energy. Specifically, our detailed calculations show that nanoclusters with much shorter total edge lengths but substantially enlarged total surface areas are energetically much more stable. As a consequence, a large majority of the nanoclusters within the 3d-, 4d-, and 5d-transition metal series are found to be fcc or hcp crystal fragments with much lower edge energies, and the widely perceived magic size of 55 is shifted to its nearby even numbers
Mechanical cleaning of food soil from a solid surface: A tribological perspective
In this work, a tribological approach was used to distinguish the synergistic effects of mechanical removal and chemical removal (i.e. dissolution) of a layer of representative food soil from a solid surface, using a tribometer, Mini Traction Machine (MTM). Gravimetric and wear measurements of the soil were used to calculate the cleaning rates of burnt tomato puree on a stainless-steel disc, and the corresponding frictional characteristics offers insight of the mechanical removal. The cleaning due to soil dissolution (chemical removal) was quantified by UVâVis measurements. The overall cleaning rates of food soil featured a linear reduction in mass over time, with a scaled removal rate k = 0.0046 sâ1 (5 N applied force and 100 mm sâ1 relative velocity), for most cases studied. It was observed that the cleaning rate can be improved with an increasing mechanical load or speed (50% from 1 to 2.5 N and 13% from 50 to 100 mm sâ1), but is independent of the initial mass. UVâVis measurements show that by increasing the load or speed the removal of chunks of burnt tomato puree was enhanced more than removal attributed to dissolution. Similar values of cleaning rates for most experimental parameters were extracted from both the gravimetric and wear measurements. Adhesion and cohesion measurements of the burnt tomato puree were conducted with a micromanipulator. It was found that adhesion forces are higher than cohesion for short soaking times, but for longer times the adhesion forces became weaker and with the additional shear rate in the MTM cleaning experiment, adhesion failure was observed in many cases by the end of the experiment. Indentation measurements showed the change in mechanical properties of the food foulant with a few minutes of soaking in water
Hair surface interactions against different chemical functional groups as a function of environment and hair condition
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