40,712 research outputs found
Graphitic-BN Based Metal-free Molecular Magnets From A First Principle Study
We perform a first principle calculation on the electronic properties of
carbon doped graphitic boron nitride graphitic BN. It was found that carbon
substitution for either boron or nitrogen atom in graphitic BN can induce
spontaneous magnetization. Calculations based on density functional theory with
the local spin density approximation on the electronic band structure revealed
a spin polarized, dispersionless band near the Fermi energy. Spin density
contours showed that the magnetization density originates from the carbon atom.
The magnetization can be attributed to the carbon 2p electron. Charge density
distribution shows that the carbon atom forms covalent bonds with its three
nearest neighbourhood. The spontaneous magnetization survives the curvature
effect in BN nanotubes, suggesting the possibility of molecular magnets made
from BN. Compared to other theoretical models of light-element or metal-free
magnetic materials, the carbon-doped BN are more experimentally accessible and
can be potentially useful.Comment: 8 pages, 4 figure
Ontology mapping neural network: An approach to learning and inferring correspondences among ontologies
An ontology mapping neural network (OMNN) is proposed in order to learn and infer correspondences among ontologies. It extends the Identical Elements Neural Network (IENN)'s ability to represent and map complex relationships. The learning dynamics of simultaneous (interlaced) training of similar tasks interact at the shared connections of the networks. The output of one network in response to a stimulus to another network can be interpreted as an analogical mapping. In a similar fashion, the networks can be explicitly trained to map specific items in one domain to specific items in another domain. Representation layer helps the network learn relationship mapping with direct training method. OMNN is applied to several OAEI benchmark test cases to test its performance on ontology mapping. Results show that OMNN approach is competitive to the top performing systems that participated in OAEI 2009
A Simple Model for Cavity Enhanced Slow Lights in Vertical Cavity Surface Emission Lasers
We develop a simple model for the slow lights in Vertical Cavity Surface
Emission Lasers (VCSELs), with the combination of cavity and population
pulsation effects. The dependences of probe signal power, injection bias
current and wavelength detuning for the group delays are demonstrated
numerically and experimentally. Up to 65 ps group delays and up to 10 GHz
modulation frequency can be achieved in the room temperature at the wavelength
of 1.3 m. The most significant feature of our VCSEL device is that the
length of active region is only several m long. Based on the experimental
parameters of quantum dot VCSEL structures, we show that the resonance effect
of laser cavity plays a significant role to enhance the group delays
Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors
II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light
elements are investigated as potential dilute magnetic semiconductors (DMS).
Based on our first-principle calculations, nitrogen doped ZnO, carbon doped
ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism
of such DMS materials can be attributed to a p-d exchange-like p-p coupling
interaction which is derived from the similar symmetry and wave function
between the impurity (p-like t_2) and valence (p) states. We also propose a
co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance
the ferromagnetic coupling and to increase the solubility and activity
Dependence of quantum correlations of twin beams on pump finesse of optical parametric oscillator
The dependence of quantum correlation of twin beams on the pump finesse of an
optical parametric oscillator is studied with a semi-classical analysis. It is
found that the phase-sum correlation of the output signal and idler beams from
an optical parametric oscillator operating above threshold depends on the
finesse of the pump field when the spurious pump phase noise generated inside
the optical cavity and the excess noise of the input pump field are involved in
the Langevin equations. The theoretical calculations can explain the previously
experimental results, quantitatively.Comment: 27 pages, 8 figure
Electromagnetic power absorption due to bumps and trenches on flat surfaces
This paper presents a study of the absorption of electromagnetic power that results from the interaction of electromagnetic waves and cylindrical bumps or trenches on flat conducting surfaces. Configurations are characterized by means of adequately selected dimensionless variables and parameters so that applicability to mathematically equivalent (but physically diverse) systems can be achieved easily. Electromagnetic fields and absorption increments caused by such surface defects are evaluated by means of a high-order integral equation method which resolves fine details of the field near the surface, and which was validated by fully analytical approaches in a range of computationally challenging cases. The computational method is also applied to problems concerning bumps and trenches on imperfect conducting planes for which analytical solutions are not available. Typically, we find that absorption is enhanced by the presence of the defects considered, although, interestingly, absorption can also be significantly reduced in some cases—such as, e.g., in the case of a trench on a conducting plane where the incident electric field is perpendicular to the plane. Additionally, it is observed that, for some small-skin-depths large-wavelengths, the absorption increment is proportional to the increase in surface area. Significant physical insight is obtained on the heating that results from various types of electromagnetic incident fields
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