150,698 research outputs found
Rate of Convergence in Nonlinear Hartree Dynamics with Factorized Initial Data
The mean field dynamics of an -particle weekly interacting Boson system
can be described by the nonlinear Hartree equation. In this paper, we present
estimates on the 1/N rate of convergence of many-body Schr\"{o}dinger dynamics
to the one-body nonlinear Hartree dynamics with factorized initial data with
two-body interaction potential in .Comment: AMS LaTex, 21 page
Quantum criticality in a Mott pn-junction in an armchair carbon nanotube
In an armchair carbon nanotube pn junction the p- and n- regions are
separated by a region of a Mott insulator, which can backscatter electrons only
in pairs. We predict a quantum-critical behavior in such a pn junction.
Depending on the junction's built-in electric field E, its conductance G scales
either to zero or to the ideal value G=4e^2/h as the temperature T is lowered.
The two types of the G(T) dependence indicate the existence, at some special
value of E, of an intermediate quantum critical point with a finite conductance
G<4e^2/h. This makes the pn junction drastically different from a simple
barrier in a Luttinger liquid.Comment: 5 pages, 1 figur
Exploration of the memory effect on the photon-assisted tunneling via a single quantum dot: A generalized Floquet theoretical approach
The generalized Floquet approach is developed to study memory effect on
electron transport phenomena through a periodically driven single quantum dot
in an electrode-multi-level dot-electrode nanoscale quantum device. The memory
effect is treated using a multi-function Lorentzian spectral density (LSD)
model that mimics the spectral density of each electrode in terms of multiple
Lorentzian functions. For the symmetric single-function LSD model involving a
single-level dot, the underlying single-particle propagator is shown to be
related to a 2 x 2 effective time-dependent Hamiltonian that includes both the
periodic external field and the electrode memory effect. By invoking the
generalized Van Vleck (GVV) nearly degenerate perturbation theory, an
analytical Tien-Gordon-like expression is derived for arbitrary order multi-
photon resonance d.c. tunneling current. Numerically converged simulations and
the GVV analytical results are in good agreement, revealing the origin of
multi- photon coherent destruction of tunneling and accounting for the
suppression of the staircase jumps of d.c. current due to the memory effect.
Specially, a novel blockade phenomenon is observed, showing distinctive
oscillations in the field-induced current in the large bias voltage limit
EffiTest: Efficient Delay Test and Statistical Prediction for Configuring Post-silicon Tunable Buffers
At nanometer manufacturing technology nodes, process variations significantly
affect circuit performance. To combat them, post- silicon clock tuning buffers
can be deployed to balance timing bud- gets of critical paths for each
individual chip after manufacturing. The challenge of this method is that path
delays should be mea- sured for each chip to configure the tuning buffers
properly. Current methods for this delay measurement rely on path-wise
frequency stepping. This strategy, however, requires too much time from ex-
pensive testers. In this paper, we propose an efficient delay test framework
(EffiTest) to solve the post-silicon testing problem by aligning path delays
using the already-existing tuning buffers in the circuit. In addition, we only
test representative paths and the delays of other paths are estimated by
statistical delay prediction. Exper- imental results demonstrate that the
proposed method can reduce the number of frequency stepping iterations by more
than 94% with only a slight yield loss.Comment: ACM/IEEE Design Automation Conference (DAC), June 201
Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines
The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
and , and , 0 and
, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur
Investigating the Physical Origin of Unconventional Low-Energy Excitations and Pseudogap Phenomena in Cuprate Superconductors
We investigate the physical origin of unconventional low-energy excitations
in cuprate superconductors by considering the effect of coexisting competing
orders (CO) and superconductivity (SC) and of quantum fluctuations and other
bosonic modes on the low-energy charge excitation spectra. By incorporating
both SC and CO in the bare Green's function and quantum phase fluctuations in
the self-energy, we can consistently account for various empirical findings in
both the hole- and electron-type cuprates, including the excess subgap
quasiparticle density of states, ``dichotomy'' in the fluctuation-renormalized
quasiparticle spectral density in momentum space, and the occurrence and
magnitude of a low-energy pseudogap being dependent on the relative gap
strength of CO and SC. Comparing these calculated results with experiments of
ours and others, we suggest that there are two energy scales associated with
the pseudogap phenomena, with the high-energy pseudogap probably of magnetic
origin and the low-energy pseudogap associated with competing orders.Comment: 10 pages, 5 figures. Invited paper for the 2006 Taiwan International
Conference on Superconductivity. Correspondence author: Nai-Chang Yeh
(e-mail: [email protected]
Correlations of supersonic boundary-layer transition on cones including effects of large axial variations in wind-tunnel noise
Transition data on sharp tip cones in two pilot low disturbance wind tunnels at Mach numbers of 3.5 and 5 were correlated in terms of noise parameters with data from several conventional wind tunnels and with data from supersonic flight tests on a transition cone. The noise parameters were developed to account for the large axial variations of the free stream noise and the very high frequency noise spectra that occurred in the low disturbance tunnels for some test conditions. The noise could be varied in these tunnels from high levels, approaching those in conventional tunnels, to extremely low levels. The correlations indicated that transition in the low disturbance tunnels was dominated by the local stream noise that was incident on the cone boundary layer unstream of the neutral stability point. The correlation results also suggested that high frequency components of the low disturbance tunnel noise spectra had significant effects on transition when the noise was incident on the boundary layer both upstream and downstream of the neutral stability point
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