25,548 research outputs found
Theory of local heating in nanoscale conductors
We report first-principles calculations of local heating in nanoscale
junctions formed by a single molecule and a gold point contact. Due to a larger
heat dissipation, the single molecule heats up less than the gold point
contact. We also find, at zero temperature, a threshold bias of
about 6 mV and 11 mV for the molecule and the point contact, respectively, is
required to excite the smallest vibrational mode and generate heat. The latter
estimate is in very good agreement with recent experimental results on the same
system. At a given external bias below , heating becomes
noticeable when the background temperature is on the order of . Above , local heating increases dramatically
with increasing bias but is also considerably suppressed by thermal dissipation
into the electrodes. The results provide a microscopic picture of
current-induced heat generation in atomic-scale structures.Comment: 4 pages, 4figure
Inelastic effects on the transport properties of alkanethiols
Using first-principles approaches we investigate local heating and the
inelastic contribution to the current for various alkanethiols sandwiched
between metal electrodes. In the absence of good heat dissipation into the bulk
electrodes, we find that the local temperature of the alkanethiols is
relatively insensitive to their length. This is due to the rates of heating and
cooling processes scaling similarly with length. On the other hand, when
considering heat dissipation into the bulk electrodes, the local temperature of
alkanethiols decreases as their length increases. We also find that the
inelastic scattering profile displays an odd-even effect with length which
compares well with experimental results. This effect is due to the alternating
direction of the CH3 group motion with respect to current flow with increasing
C atoms in the chain, and is very sensitive to the structure of the
carbon-sulfur-gold bond. Inelastic scattering profiles can therefore help
illuminate the bonding configuration of molecules to metallic surfaces.Comment: 5 pages, 4 figure
Effect of electron-phonon scattering on shot noise in nanoscale junctions
We investigate the effect of electron-phonon inelastic scattering on shot
noise in nanoscale junctions in the regime of quasi-ballistic transport. We
predict that when the local temperature of the junction is larger than its
lowest vibrational mode energy , the inelastic contribution to shot noise
(conductance) increases (decreases) with bias as (). The
corresponding Fano factor thus increases as . We also show that the
inelastic contribution to the Fano factor saturates with increasing thermal
current exchanged between the junction and the bulk electrodes to a value
which, for , is independent of bias. A measurement of shot noise may
thus provide information about the local temperature and heat dissipation in
nanoscale conductors.Comment: 4 pages, 2 figure
Mixed principal eigenvalues in dimension one
This is one of a series of papers exploring the stability speed of
one-dimensional stochastic processes. The present paper emphasizes on the
principal eigenvalues of elliptic operators.
The eigenvalue is just the best constant in the -Poincar\'e inequality
and describes the decay rate of the corresponding diffusion process. We present
some variational formulas for the mixed principal eigenvalues of the operators.
As applications of these formulas, we obtain case by case explicit estimates, a
criterion for positivity, and an approximating procedure for the eigenvalue.Comment: 45 pages; Front. Math. China, 201
A Finite Exact Representation of Register Automata Configurations
A register automaton is a finite automaton with finitely many registers
ranging from an infinite alphabet. Since the valuations of registers are
infinite, there are infinitely many configurations. We describe a technique to
classify infinite register automata configurations into finitely many exact
representative configurations. Using the finitary representation, we give an
algorithm solving the reachability problem for register automata. We moreover
define a computation tree logic for register automata and solve its model
checking problem.Comment: In Proceedings INFINITY 2013, arXiv:1402.661
A case of renal cell carcinoma metastasizing to invasive ductal breast carcinoma
Tumor-to-tumor metastasis is an uncommon but well-documented phenomenon. We present a case of a clear cell renal cell carcinoma (RCC) metastasizing to an invasive ductal carcinoma (IDC) of the breast. A 74-year-old woman with a past history of clear cell RCC status after radical nephrectomy underwent right modified radical mastectomy for an enlarging breast mass 3 years after nephrectomy. Histological examination revealed a small focus with distinct morphological features similar to clear cell RCC encased in the otherwise typical IDC. Immunohistochemical studies showed that this focus was positive for CD10 and vimentin, in contrast to the surrounding IDC, which was negative for both markers and positive for Her2/neu. Based on the histological and immunohistochemical features, the patient was diagnosed with metastasis of clear cell RCC to the breast IDC. To the best of our knowledge, this is the first reported case of a breast neoplasm as the recipient tumor in tumor-to-tumor metastasis
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