767 research outputs found
Kondo effect in coupled quantum dots under magnetic fields
The Kondo effect in coupled quantum dots is investigated theoretically under
magnetic fields. We show that the magnetoconductance (MC) illustrates peak
structures of the Kondo resonant spectra. When the dot-dot tunneling coupling
is smaller than the dot-lead coupling (level broadening), the
Kondo resonant levels appear at the Fermi level (). The Zeeman splitting
of the levels weakens the Kondo effect, which results in a negative MC. When
is larger than , the Kondo resonances form bonding and
anti-bonding levels, located below and above , respectively. We observe a
positive MC since the Zeeman splitting increases the overlap between the levels
at . In the presence of the antiferromagnetic spin coupling between the
dots, the sign of MC can change as a function of the gate voltage.Comment: 6 pages, 3 figure
Data compression approach for long-term monitoring of pavement structures
Pavement structures are designed to withstand continuous damage during their design life. Damage starts as soon as the pavement is open to traffic and increases with time. If maintenance activities are not considered in the initial design or considered but not applied during the service life, damage will grow to a point where rehabilitation may be the only and most expensive option left. In order to monitor the evolution of damage and its severity in pavement structures, a novel data compression approach based on cumulative measurements from a piezoelectric sensor is presented in this paper. Specifically, the piezoelectric sensor uses a thin film of polyvinylidene fluoride to sense the energy produced by the micro deformation generated due to the application of traffic loads. Epoxy solution has been used to encapsulate the membrane providing hardness and flexibility to withstand the high-loads and the high-temperatures during construction of the asphalt layer. The piezoelectric sensors have been exposed to three months of loading (approximately 1.0 million loads of 65 kN) at the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) fatigue carrousel. Notably, the sensors survived the construction and testing. Reference measurements were made with a commercial conventional strain gauge specifically designed for measurements in hot mix asphalt layers. Results from the carrousel successfully demonstrate that the novel approach can be considered as a good indicator of damage progression, thus alleviating the need to measure strains in pavement for the purpose of damage tracking
Validation of a Novel Sensing Approach for Continuous Pavement Monitoring Using Full-Scale APT Testing
The objective of this paper is to present a novel approach for the continuous monitoring of pavement condition through the use of combined piezoelectric sensing and novel condition-based interpretation methods. The performance of the developed approach is validated for the detection of bottom-up fatigue cracking through full-scale accelerated pavement testing (APT). The innovative piezoelectric sensors are installed at the bottom of a thin 102 mm (4 in.) asphalt layer. The structure is then loaded until failure (up to 1 million loading cycles in this study). The condition-based approach, used in this work, does not rely on stain measurements and allows users to bypass the need for any structural or finite-element models. Instead, the data compression approach relies on variations in strain energy harvested by smart sensors to track changes in material and structural conditions. Falling weight deflectometer (FWD) measurements and visual inspections were used to validate the observations from the sensing system. The results in this paper present a first large-scale validation in pavement structures for a piezopowered sensing system combined with a new response-only based approach for data reduction and interpretation. The proposed data analysis method has demonstrated a very early detection capability compared to classical inspection methods, which unveils a huge potential for improved pavement monitoring
Kondo resonant spectra in coupled quantum dots
The Kondo effect in coupled quantum dots is investigated from the viewpoint
of transmission spectroscopy using the slave-boson formalism of the Anderson
model. The antiferromagnetic spin-spin coupling between the dots is taken
into account. Conductance through the dots connected in a series is
characterized by the competition between the dot-dot tunneling coupling
and the level broadening in the dots (dot-lead coupling). When
, the Kondo resonance is formed between each dot and lead,
which is replaced by a spin-singlet state in the dots at low gate voltages. The
gate voltage dependence of has a sharp peak of in height in the
crossover region between the Kondo and spin-singlet states. The sharp peak of
survives when the energy levels are different between the dots. When , the "molecular levels" between the Kondo resonant states appear;
the Kondo resonant peaks are located below and above the Fermi level in the
leads at low gate voltages. The gate voltage dependence of has a broad
peak, which is robust against . The broad peak splits into two peaks when
the energy levels are different, reflecting the formation of the asymmetric
molecular levels between the Kondo resonant states.Comment: 21 pages, 8 figures, to appear in Phys. Rev.
Electron Transport through T-Shaped Double-Dots System
Correlation effects on electron transport through a system of T-shaped
double-dots are investigated, for which only one of the dots is directly
connected to the leads. We evaluate the local density of states and the
conductance by means of the non-crossing approximation at finite temperatures
as well as the slave-boson mean field approximation at zero temperature. It is
found that the dot which is not directly connected to the leads considerably
influences the conductance, making its behavior quite different from the case
of a single-dot system. In particular, we find a novel phenomenon in the Kondo
regime with a small inter-dot coupling, i.e.
Fano-like suppression of the Kondo-mediated conductance, when two dot levels
coincide with each other energetically.Comment: 6 pages,7 figure
Spin-Polarized Transprot through Double Quantum Dots
We investigate spin-polarized transport phenomena through double quantum dots
coupled to ferromagnetic leads in series. By means of the slave-boson
mean-field approximation, we calculate the conductance in the Kondo regime for
two different configurations of the leads: spin-polarization of two
ferromagnetic leads is parallel or anti-parallel. It is found that transport
shows some remarkable properties depending on the tunneling strength between
two dots. These properties are explained in terms of the Kondo resonances in
the local density of states.Comment: 8 pages, 11 figure
Faster Enumeration-based Lattice Reduction:Root Hermite Factor k1/(2k) Time kk/8+o(k)
International audienc
Modified Perturbation Theory Applied to Kondo-Type Transport through a Quantum Dot under a Magnetic Field
Linear conductance through a quantum dot is calculated under a finite
magnetic field using the modified perturbation theory. The method is based on
the second-order perturbation theory with respect to the Coulomb repulsion, but
the self-energy is modified to reproduce the correct atomic limit and to
fulfill the Friedel sum rule exactly. Although this method is applicable only
to zero temperature in a strict sense, it is approximately extended to finite
temperatures. It is found that the conductance near electron-hole symmetry is
suppressed by the application of the magnetic field at low temperatures.
Positive magnetoconductance is observed in the case of large electron-hole
asymmetry.Comment: 4pages, 5 figure
Solving the Shortest Vector Problem in Lattices Faster Using Quantum Search
By applying Grover's quantum search algorithm to the lattice algorithms of
Micciancio and Voulgaris, Nguyen and Vidick, Wang et al., and Pujol and
Stehl\'{e}, we obtain improved asymptotic quantum results for solving the
shortest vector problem. With quantum computers we can provably find a shortest
vector in time , improving upon the classical time
complexity of of Pujol and Stehl\'{e} and the of Micciancio and Voulgaris, while heuristically we expect to find a
shortest vector in time , improving upon the classical time
complexity of of Wang et al. These quantum complexities
will be an important guide for the selection of parameters for post-quantum
cryptosystems based on the hardness of the shortest vector problem.Comment: 19 page
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