11,879 research outputs found
Nanocrystalline iron at high pressure
X-ray diffraction measurements were performed on nanocrystalline iron up to 46 GPa. For nanocrystalline epsilon-Fe, analysis of lattice parameter data provides a bulk modulus, K, of 179±8 GPa and a pressure derivative of the bulk modulus, K[prime], of 3.6±0.7, similar to the large-grained control sample. The extrapolated zero-pressure unit cell volume of nanocrystalline epsilon-Fe is 22.9±0.2 Å^3, compared to 22.3±0.2 Å^3 for large-grained epsilon-Fe. No significant grain growth was observed to occur under pressure
Multi-Atomic Mirror for Perfect Reflection of Single Photons in A Wide Band of Frequency
A resonant two level atom doped in one dimensional waveguide behaves as a
mirror, but this single-atom "mirror" can only reflect single photon perfectly
at a specific frequency. For a one dimensional coupled-resonator waveguide, we
propose to extend the perfect reflection region from a specific frequency to a
wide band by placing many atoms individually in the resonators in a finite
coordinate region of the waveguide. Such a doped resonator array promises us to
control the propagation of a practical photon wave packet with certain momentum
distribution instead of a single photon, which is ideally represented by a
plane wave with specific momentum. The studies based on the discrete-coordinate
scattering theory display that such hybrid structure indeed provides a
near-perfect reflection for single photon in a wide band. We also calculated
photon group velocity distribution, which shows that the perfect reflection
with wide band exactly corresponds to the stopping light region.Comment: 8 pages, 10 figure
Temperature dependence of the conductivity of the electronic crystal
We study the temperature dependence of the conductivity of the 2D electronic
solid. In realistic samples, a domain structure forms in the solid and each
domain randomly orients in the absence of the in-plane field. At higher
temperature, the electron transport is governed by thermal activation form of
. The impurities will localize the
electron states along the edges of the crystal domains. At sufficient low
temperature, another transport mechanism called Mott's variable range hopping
mechanism, similar to that in a disorder insulator takes effect. We show that
as the temperature decreases, a crossover from the fixed range hopping of the
transport to the variable range hopping of transport in the 2D electron system
may be experimentally observed.Comment: 4 pages,1 figure
Vibrations of micro-eV energies in nanocrystalline microstructures
The phonon density of states of nanocrystalline bcc Fe and nanocrystalline fcc Ni3Fe were measured by inelastic neutron scattering in two different ranges of energy. As has been reported previously, the nanocrystalline materials showed enhancements in their phonon density of states at energies from 2 to 15 meV, compared to control samples composed of large crystals. The present measurements were extended to energies in the micro-eV range, and showed significant, but smaller, enhancements in the number of modes in the energy range from 5 to 18 mueV. These modes of micro-eV energies provide a long-wavelength limit that bounds the fraction of modes at milli-eV energies originating with the cooperative dynamics of the nanocrystalline microstructure
Reactive direction control for a mobile robot: A locust-like control of escape direction emerges when a bilateral pair of model locust visual neurons are integrated
Locusts possess a bilateral pair of uniquely identifiable visual neurons that respond vigorously to
the image of an approaching object. These neurons are called the lobula giant movement
detectors (LGMDs). The locust LGMDs have been extensively studied and this has lead to the
development of an LGMD model for use as an artificial collision detector in robotic applications.
To date, robots have been equipped with only a single, central artificial LGMD sensor, and this
triggers a non-directional stop or rotation when a potentially colliding object is detected. Clearly,
for a robot to behave autonomously, it must react differently to stimuli approaching from
different directions. In this study, we implement a bilateral pair of LGMD models in Khepera
robots equipped with normal and panoramic cameras. We integrate the responses of these LGMD
models using methodologies inspired by research on escape direction control in cockroaches.
Using ‘randomised winner-take-all’ or ‘steering wheel’ algorithms for LGMD model integration,
the khepera robots could escape an approaching threat in real time and with a similar
distribution of escape directions as real locusts. We also found that by optimising these
algorithms, we could use them to integrate the left and right DCMD responses of real jumping
locusts offline and reproduce the actual escape directions that the locusts took in a particular
trial. Our results significantly advance the development of an artificial collision detection and
evasion system based on the locust LGMD by allowing it reactive control over robot behaviour.
The success of this approach may also indicate some important areas to be pursued in future
biological research
Probing Topcolor-Assisted Technicolor from Like-sign Top Pair Production at LHC
The topcolor-assisted technicolor (TC2) theory predicts tree-level
flavor-changing neutral-current (FCNC) top quark Yukawa couplings with
top-pions. Such FCNC interactions will induce like-sign top quark pair
productions at CERN Large Hadron Collider (LHC). While these rare productions
are far below the observable level in the Standard Model and other popular new
physics models such as the Minimal Supersymmetric Model, we find that in a
sound part of parameter space the TC2 model can enhance the production cross
sections to several tens of fb and thus may be observable at the LHC due to
rather low backgrounds. Searching for these productions at the LHC will serve
as an excellent probe for the TC2 model.Comment: 10 pages, 6 fig
Intensification-driven tabu search for the minimum differential dispersion problem
The minimum differential dispersion problem is a NP-hard combinatorial optimization problem with numerous relevant applications. In this paper, we propose an intensification-driven tabu search algorithm for solving this computationally challenging problem by integrating a constrained neighborhood, a solution-based tabu strategy, and an intensified search mechanism to create a search that effectively exploits the elements of intensification and diversification. We demonstrate the competitiveness of the proposed algorithm by presenting improved new best solutions for 127 out of 250 benchmark instances (>50%). We study the search trajectory of the algorithm to shed light on its behavior and investigate the spatial distribution of high-quality solutions in the search space to motivate the design choice of the intensified search mechanism
Solution-based Tabu Search for the Maximum Min-sum Dispersion Problem
The maximum min-sum dispersion problem (Max-Minsum DP) is an important representative of a large class of dispersion problems. Having numerous applications in practice, the NP-hard Max-Minsum DP is however computationally challenging. This paper introduces an effective solution-based tabu search (SBTS) algorithm for solving the Max-Minsum DP approximately. SBTS is characterized by the joint use of hash functions to determine the tabu status of candidate solutions and a parametric constrained swap neighborhood to enhance computational efficiency. Experimental results on 140 benchmark instances commonly used in the literature demonstrate that the proposed algorithm competes favorably with the state-of-the-art algorithms both in terms of solution quality and computational efficiency. In particular, SBTS improves the best-known results for 80 out of the 140 instances, while matching 51 other best-known solutions. We conduct a computational analysis to identify the respective roles of the hash functions and the parametric constrained swap neighborhood
Bosonization of One-Dimensional Exclusons and Characterization of Luttinger Liquids
We achieve a bosonization of one-dimensional ideal gas of exclusion
statistics at low temperatures, resulting in a new variant of
conformal field theory with compactified radius . These
ideal excluson gases exactly reproduce the low- critical properties of
Luttinger liquids, so they can be used to characterize the fixed points of the
latter. Generalized ideal gases with mutual statistics and non-ideal gases with
Luttinger-type interactions have also similar behavior, controlled by an
effective statistics varying in a fixed-point line.Comment: 13 pages, revte
- …