181 research outputs found
Oscillation criteria for nonlinear second-order differential equations with damping
Some new oscillation criteria are given for general nonlinear second order ordinary differential equations
with damping of the form x′′ + p(t)x′ + q(t) f (x) = 0, where f is with or without monotonicity. Our
results generalize and extend some earlier results of Deng.Наведено деякі нові осцнляційні критерії для загальних нелінійних звичайних диференціальних рівнянь другого порядку із затуханням вигляду x" + p(t)x' + q(t)f(x) = 0, де функція f або монотонна, або немонотонна. Наведені результати узагальнюють та розширюють деякі результати, отримані раніше Денгом
Effects of long-range disorder and electronic interactions on the optical properties of graphene quantum dots
We theoretically investigate the effects of long-range disorder and
electron-electron interactions on the optical properties of hexagonal armchair
graphene quantum dots consisting of up to 10806 atoms. The numerical
calculations are performed using a combination of tight-binding, mean-field
Hubbard and configuration interaction methods. Imperfections in the graphene
quantum dots are modelled as a long-range random potential landscape, giving
rise to electron-hole puddles. We show that, when the electron-hole puddles are
present, tight-binding method gives a poor description of the low-energy
absorption spectra compared to meanfield and configuration interaction
calculation results. As the size of the graphene quantum dot is increased, the
universal optical conductivity limit can be observed in the absorption
spectrum. When disorder is present, calculated absorption spectrum approaches
the experimental results for isolated monolayer of graphene sheet
Protecting the operation from general and residual errors by continuous dynamical decoupling
We study the occurrence of errors in a continuously decoupled two-qubit state
during a quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.Comment: Extended version of arXiv:1005.1666. To appear in PR
Effects of random atomic disorder on the magnetic stability of graphene nanoribbons with zigzag edges
We investigate the effects of randomly distributed atomic defects on the
magnetic properties of graphene nanoribbons with zigzag edges using an extended
mean-field Hubbard model. For a balanced defect distribution among the
sublattices of the honeycomb lattice in the bulk region of the ribbon, the
ground state antiferromagnetism of the edge states remains unaffected. By
analyzing the excitation spectrum, we show that while the antiferromagnetic
ground state is susceptible to single spin flip excitations from edge states to
magnetic defect states at low defect concentrations, it's overall stability is
enhanced with respect to the ferromagnetic phase.Comment: 5 pages, 4 figure
Embedded NiTi wires for improved dynamic thermomechanical performance of silicone elastomers
The extraordinary properties of shape memory NiTi alloy are combined with the inherent viscoelastic behavior of a silicon elastomer. NiTi wires are incorporated in a silicon elastomer matrix. Benefits include features as electrical/thermal conductivity, reinforcement along with enhanced damping performance and flexibility. To gain more insight of this composite, a comprehensive dynamic thermomechanical analysis is performed and the temperature- as well as frequency-dependent storage modulus and the mechanical loss factor are obtained. The analyses are realized for the composite and single components. Moreover, the models to express the examined properties and their temperature along with the frequency dependencies are also presented
COMPARISON OF VIRTUAL FIELDS METHOD, PARALLEL NETWORK MATERIAL MODEL AND FINITE ELEMENT UPDATING FOR MATERIAL PARAMETER DETERMINATION
Extracting material parameters from test specimens is very intensive in terms of cost and time, especially for viscoelastic material models, where the parameters are dependent of time (frequency), temperature and environmental conditions. Therefore, three different methods for extracting these parameters were tested. Firstly, digital image correlation combined with virtual fields method, secondly, a parallel network material model and thirdly, finite element updating. These three methods are shown and the results are compared in terms of accuracy and experimental effort
Computational speed-up with a single qudit
Quantum algorithms are known for providing more efficient solutions to
certain computational tasks than any corresponding classical algorithm. Here we
show that a single qudit is sufficient to implement an oracle based quantum
algorithm, which can solve a black-box problem faster than any classical
algorithm. For permutation functions defined on a set of elements,
deciding whether a given permutation is even or odd, requires evaluation of the
function for at least two elements. We demonstrate that a quantum circuit with
a single qudit can determine the parity of the permutation with only one
evaluation of the function. Our algorithm provides an example for quantum
computation without entanglement since it makes use of the pure state of a
qudit. We also present an experimental realization of the proposed quantum
algorithm with a quadrupolar nuclear magnetic resonance using a single
four-level quantum system, i.e., a ququart.Comment: Combined version of arXiv:1403.5861 [quant-ph] and arXiv:1406.3579
[quant-ph
Effect of molecular and electronic structure on the light harvesting properties of dye sensitizers
The systematic trends in structural and electronic properties of perylene
diimide (PDI) derived dye molecules have been investigated by DFT calculations
based on projector augmented wave (PAW) method including gradient corrected
exchange-correlation effects. TDDFT calculations have been performed to study
the visible absorbance activity of these complexes. The effect of different
ligands and halogen atoms attached to PDI were studied to characterize the
light harvesting properties. The atomic size and electronegativity of the
halogen were observed to alter the relaxed molecular geometries which in turn
influenced the electronic behavior of the dye molecules. Ground state molecular
structure of isolated dye molecules studied in this work depends on both the
halogen atom and the carboxylic acid groups. DFT calculations revealed that the
carboxylic acid ligands did not play an important role in changing the
HOMO-LUMO gap of the sensitizer. However, they serve as anchor between the PDI
and substrate titania surface of the solar cell or photocatalyst. A
commercially available dye-sensitizer, ruthenium bipyridine (RuBpy), was also
studied for electronic and structural properties in order to make a comparison
with PDI derivatives for light harvesting properties. Results of this work
suggest that fluorinated, chlorinated, brominated, and iyodinated PDI compounds
can be useful as sensitizers in solar cells and in artificial photosynthesis.Comment: Single pdf file, 14 pages with 7 figures and 4 table
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