8,865 research outputs found
An integral representation, some inequalities, and complete monotonicity of Bernoulli numbers of the second kind
In the paper, the authors discover an integral representation, some
inequalities, and complete monotonicity of Bernoulli numbers of the second
kind.Comment: 10 page
Trigonometric protocols for shortcuts to adiabatic transport of cold atoms in anharmonic traps
Shortcuts to adiabaticity have been proposed to speed up the "slow" adiabatic
transport of an atom or a wave packet of atoms. However, the freedom of the
inverse engineering approach with appropriate boundary conditions provides
thousands of trap trajectories for different purposes, for example, time and
energy minimizations. In this paper, we propose trigonometric protocols for
fast and robust atomic transport, taking into account cubic or quartic
anharmonicities. The numerical results have illustrated that such trigonometric
protocols, particular cosine ansatz, is more robust and the corresponding final
energy excitation is smaller, as compared to sine trajectories implemented in
previous experiments.Comment: 5 pages, 5 figure
Studying the molecule in the Bethe-Salpeter equation approach
We study the possible bound states of the system in the Bethe-Salpeter
(BS) formalism in the ladder and instantaneous approximations. By solving the
BS equation numerically with the kernel containing one-particle exchange
diagrams and introducing three different form factors (monopole, dipole, and
exponential form factors) at the vertices, we investigate whether the isoscalar
and isovector bound states may exist, respectively. We find that
could be accommodated as a molecule, whereas the
interpretation of as a molecule is disfavored. The bottom
analog of may exist but that of does not.Comment: 17 pages, 6 figures, and 4 table
Calculation of divergent photon absorption in ultrathin films of a topological insulator
We perform linear and non-linear photon absorption calculations in
topological insulator ultra-thin films on a substrate. Due to the unique band
structure of the coupled topological surface states, novel features are
observed for suitable photon frequencies, including a divergent edge
singularity in one-photon absorption process and a significantly enhancement in
two-photon absorption process. The resonanct frequencies can be controlled by
tuning the energy difference and coupling of the top and bottom surface states.
Such unique linear and nonlinear optical properties make ultra-thin films of
topological insulators promising material building blocks for tunable
high-efficiency nanophotonic devices.Comment: 6 pages, 3 figure
Theoretical Modeling of Tribochemical Reaction on Pt and Au Contacts: Mechanical Load and Catalysis
Micro-electro-mechanical system and nano-electro-mechanical system (MEMS and
NEMS) transistors are considered promising for size-reducing and
power-maximizing electronic devices. However, the tribopolymer which forms due
to the mechanical load to the surface contacts affects the conductivity between
the contacts dramatically. This is one of the challenging problems that prevent
widespread practical use of these otherwise promising devices. Here, we use
density functional theory (DFT) to investigate the mechanisms of tribopolymer
formation, including normal mechanical loading, the catalytic effect, as well
as the electrochemical effect of the metal contacts. We select benzene select
as the background gas, because it is one of the most common and severe
hydrocarbon contaminants. Two adsorption cases are considered: one is benzene
on the reactive metal surface, Pt(111), and the other is benzene on the noble
metal, Au(111). We demonstrate that the formation of tribopolymer is induced
both by the mechanical load and by the catalytic effect of the contact. First,
benzene molecules are adsorbed on the Pt surfaces. Then, due to the closure of
the Pt contacts, stress is applied to the adsorbates, making the C-H bonds more
fragile. As the stress increases further, H atoms are pressed close to the Pt
substrate and begin to bond with Pt atoms. Thus Pt acts as a catalyst,
accelerating the dehydrogenation process. When there is voltage applied across
the contacts, the catalytic effect is enhanced by electrochemistry. Finally,
due to the loss of H atoms, C atoms become more reactive and link together or
pile up to form tribopolymer. By understanding these mechanisms, we provide
guidance on design strategies for suppressing tribopolymer formation.Comment: 14 pages, 7 figure
Some Bernstein functions and integral representations concerning harmonic and geometric means
It is general knowledge that the harmonic mean
and that the geometric mean
, where and are two positive numbers. In the paper,
the authors show by several approaches that the harmonic mean
and the geometric mean are all
Bernstein functions of and establish integral
representations of the means and .Comment: 19 page
Second Order Linear Energy Stable Schemes for Allen-Cahn Equations with Nonlocal Constraints
We present a set of linear, second order, unconditionally energy stable
schemes for the Allen-Cahn equation with nonlocal constraints that preserves
the total volume of each phase in a binary material system. The energy
quadratization strategy is employed to derive the energy stable semi-discrete
numerical algorithms in time. Solvability conditions are then established for
the linear systems resulting from the semi-discrete, linear schemes. The fully
discrete schemes are obtained afterwards by applying second order finite
difference methods on cell-centered grids in space. The performance of the
schemes are assessed against two benchmark numerical examples, in which
dynamics obtained using the volumepreserving Allen-Cahn equations with nonlocal
constraints is compared with those obtained using the classical Allen-Cahn as
well as the Cahn-Hilliard model, respectively, demonstrating slower dynamics
when volume constraints are imposed as well as their usefulness as alternatives
to the Cahn-Hilliard equation in describing phase evolutionary dynamics for
immiscible material systems while preserving the phase volumes. Some
performance enhancing, practical implementation methods for the linear energy
stable schemes are discussed in the end
Negative refraction index of the quantum lossy left-handed transmission lines affected by the displaced squeezed Fock state and dissipation
Quantum lossy left-handed transmission lines (LHTLs) are central to the
miniaturized application in microwave band. This work discusses the NRI of the
quantized lossy LHTLs in the presence of the resistance and the conductance in
a displaced squeezed Fock state (DSFS). And the results show some novel
specific quantum characteristics of NRI caused by the DSFS and dissipation,
which may be significant for its miniaturized application in a suit of novel
microwave devices.Comment: 11 pages,5 figure
Studying the bound state of the system in the Bethe-Salpeter formalism
In this work, we study the molecule in the Bethe-Salpeter (BS)
equation approach. With the kernel containing one-particle-exchange diagrams
and introducing two different form factors (monopole form factor and dipole
form factor) in the vertex, we solve the BS equation numerically in the
covariant instantaneous approximation. We investigate the isoscalar and
isovector systems, and we find cannot be a
molecule
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