3,724 research outputs found
Counting statistics of tunneling through a single molecule: effect of distortion and displacement of vibrational potential surface
We analyze the effects of a distortion of the nuclear potential of a
molecular quantum dot (QD), as well as a shift of its equilibrium position, on
nonequilibrium-vibration-assisted tunneling through the QD with a single level
() coupled to the vibrational mode. For this purpose, we derive an
explicit analytical expression for the Franck-Condon (FC) factor for a
displaced-distorted oscillator surface of the molecule and establish rate
equations in the joint electron-phonon representation to examine the
current-voltage characteristics and zero-frequency shot noise, and skewness as
well. Our numerical analyses shows that the distortion has two important
effects. The first one is that it breaks the symmetry between the excitation
spectra of the charge states, leading to asymmetric tunneling properties with
respect to and . Secondly, distortion (frequency
change of the oscillator) significantly changes the voltage-activated cascaded
transition mechanism, and consequently gives rise to a different nonequilibrium
vibrational distribution from that of the case without distortion. Taken in
conjunction with strongly modified FC factors due to distortion, this results
in some new transport features: the appearance of strong NDC even for a
single-level QD with symmetric tunnel couplings; a giant Fano factor even for a
molecule with an extremely weak electron-phonon interaction; and enhanced
skewness that can have a large negative value under certain conditions.Comment: 29 pages, 11 figures, published versio
Nemeth in a Box: Unpacking Tools to Build Success in Math for Students with Visual Impairments
Students with visual impairments can be successful in math learning if they are provided with accessible materials, appropriate accommodations, and knowledgeable teachers. Four teachers of students with visual impairment designed a set of activities to build middle school students' knowledge of the braille code while engaging in math activities. The activities are described, and the authors provide strategies for successfully including students in general education math classes. 
A joint time-dependent density-functional theory for excited states of electronic systems in solution
We present a novel joint time-dependent density-functional theory for the
description of solute-solvent systems in time-dependent external potentials.
Starting with the exact quantum-mechanical action functional for both electrons
and nuclei, we systematically eliminate solvent degrees of freedom and thus
arrive at coarse-grained action functionals which retain the highly accurate
\emph{ab initio} description for the solute and are, in principle, exact. This
procedure allows us to examine approximations underlying popular embedding
theories for excited states. Finally, we introduce a novel approximate action
functional for the solute-water system and compute the solvato-chromic shift of
the lowest singlet excited state of formaldehyde in aqueous solution, which is
in good agreement with experimental findings.Comment: 11 page
Anomalous suppression of the shot noise in a nanoelectromechanical system
In this paper we report a relaxation-induced suppression of the noise for a
single level quantum dot coupled to an oscillator with incoherent dynamics in
the sequential tunneling regime. It is shown that relaxation induces
qualitative changes in the transport properties of the dot, depending on the
strength of the electron-phonon coupling and on the applied voltage. In
particular, critical thresholds in voltage and relaxation are found such that a
suppression below 1/2 of the Fano factor is possible. Additionally, the current
is either enhanced or suppressed by increasing relaxation, depending on bias
being greater or smaller than the above threshold. These results exist for any
strength of the electron-phonon coupling and are confirmed by a four states toy
model.Comment: 7 pages, 7 eps figures, submitted to PRB; minor changes in the
introductio
NSAIDs for analgesia in the era of COVID-19
Globally, non-steroidal anti-inflammatory drugs (NSAIDs) are highly used to treat pain. With the rise of the COVID-19 pandemic, the safety of NSAIDs use has been called into question. These concerns are worthy of review. At present, there is no compelling data showing that NSAIDs worsen the severity of COVID-19 symptoms or increase one\u27s likelihood of contracting the illness. For patients in pain and without symptoms that could potentially be attributed to COVID-19 (cough, fevers/chills, lethargy, myalgias, anosmia and so on), NSAIDs should continue to remain a viable option to provide analgesia to patients in need
Dynamics of Bulk vs. Nanoscale WS_2: Local Strain and Charging Effects
We measured the infrared vibrational properties of bulk and nanoparticle
WS in order to investigate the structure-property relations in these novel
materials. In addition to the symmetry-breaking effects of local strain,
nanoparticle curvature modifies the local charging environment of the bulk
material. Performing a charge analysis on the \emph{xy}-polarized E
vibrational mode, we find an approximate 1.5:1 intralayer charge difference
between the layered 2H material and inorganic fullerene-like (IF)
nanoparticles. This effective charge difference may impact the solid-state
lubrication properties of nanoscale metal dichalcogenides.Comment: 6 pages, 5 figure
Entanglement and chaos in the kicked top
The standard kicked top involves a periodically kicked angular momentum. By
considering this angular momentum as a collection of entangled spins, we
compute the bipartite entanglement dynamics as a function of the dynamics of
the classical counterpart. Our numerical results indicate that the entanglement
of the quantum top depends on the specific details of the dynamics of the
classical top rather than depending universally on the global properties of the
classical regime. These results are grounded on linking the entanglement rate
to averages involving the classical angular momentum, thereby explaining why
regular dynamics can entangle as efficiently as the classically chaotic regime.
The findings are in line with previous results obtained with a 2-particle top
model, and we show here that the standard kicked top can be obtained as a
limiting case of the 2-particle top
On the Prospects for Laser Cooling of TlF
We measure the upper state lifetime and two ratios of vibrational branching
fractions f_{v'v} on the B^{3}\Pi_{1}(v') - X^{1}\Sigma^{+}(v) transition of
TlF. We find the B state lifetime to be 99(9) ns. We also determine that the
off-diagonal vibrational decays are highly suppressed: f_{01}/f_{00} <
2x10^{-4} and f_{02}/f_{00} = 1.10(6)%, in excellent agreement with their
predicted values of f_{01}/f_{00} < 8x10^{-4} and f_{02}/f_{00} = 1.0(2)% based
on Franck-Condon factors calculated using Morse and RKR potentials. The
implications of these results for the possible laser cooling of TlF and
fundamental symmetries experiments are discussed.Comment: 5 pages, 2 figure
Exact Coupling Coefficient Distribution in the Doorway Mechanism
In many--body and other systems, the physics situation often allows one to
interpret certain, distinct states by means of a simple picture. In this
interpretation, the distinct states are not eigenstates of the full
Hamiltonian. Hence, there is an interaction which makes the distinct states act
as doorways into background states which are modeled statistically. The crucial
quantities are the overlaps between the eigenstates of the full Hamiltonian and
the doorway states, that is, the coupling coefficients occuring in the
expansion of true eigenstates in the simple model basis. Recently, the
distribution of the maximum coupling coefficients was introduced as a new,
highly sensitive statistical observable. In the particularly important regime
of weak interactions, this distribution is very well approximated by the
fidelity distribution, defined as the distribution of the overlap between the
doorway states with interaction and without interaction. Using a random matrix
model, we calculate the latter distribution exactly for regular and chaotic
background states in the cases of preserved and fully broken time--reversal
invariance. We also perform numerical simulations and find excellent agreement
with our analytical results.Comment: 22 pages, 4 figure
- âŠ