632 research outputs found
Half Metallicity in Hybrid BCN Nanoribbons
We report a first-principles electronic-structure calculation on C and BN
hybrid zigzag nanoribbons. We find that half-metallicity can arise in the
hybrid nanoribbons even though stand-alone C or BN nanoribbon possesses a
finite band gap. This unexpected half-metallicity in the hybrid nanos-tructures
stems from a competition between the charge and spin polarizations, as well as
from the pi orbital hybridization between C and BN. Our results point out a
possibility of making spintronic devices solely based on nanoribbons and a new
way of designing metal-free half metals
A new extended matrix KP hierarchy and its solutions
With the square eigenfunctions symmetry constraint, we introduce a new
extended matrix KP hierarchy and its Lax representation from the matrix KP
hierarchy by adding a new flow. The extended KP hierarchy contains two
time series and and eigenfunctions and adjoint
eigenfunctions as components. The extended matrix KP hierarchy and its
-reduction and reduction include two types of matrix KP hierarchy
with self-consistent sources and two types of (1+1)-dimensional reduced matrix
KP hierarchy with self-consistent sources. In particular, the first type and
second type of the 2+1 AKNS equation and the Davey-Stewartson equation with
self-consistent sources are deduced from the extended matrix KP hierarchy. The
generalized dressing approach for solving the extended matrix KP hierarchy is
proposed and some solutions are presented. The soliton solutions of two types
of 2+1-dimensional AKNS equation with self-consistent sources and two types of
Davey-Stewartson equation with self-consistent sources are studied.Comment: 17 page
Experimental characterisation of dynamic properties of an all-FRP truss bridge
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordFibre Reinforced Polymers (FRPs) have increasingly been utilised for construction of pedestrian bridges due to high strength- and stiffness-to-weight ratios, low maintenance costs and quick installation. Their relatively low mass and stiffness make these bridges potentially susceptible to vibration serviceability problems, which increasingly govern the design. Currently, the wider application of FRPs in civil engineering is hindered by the lack of experimental insight in dynamic performance of as-built structures. This paper presents an experimental investigation on a 25, m long glass-FRP truss footbridge in Italy. Ambient vibration tests were conducted to identify the dynamic properties. The peak-picking method and stochastic subspace identification approach were employed for modal parameter identification. The two methods produced very consistent results. Eight vibration modes were identified in the frequency range up to 10, Hz. Two lateral flexural vibration modes having natural frequencies of 5.8 and 9.6, Hz were identified, as well as two vertical flexural modes (at 7.5 and 8.1, Hz) and four torsional modes (at 2.1, 2.7, 4.8 and 9.3, Hz). Damping ratios for all modes up to 10, Hz except the eighth mode were above 1.2%.Engineering and Physical Sciences Research Council (EPSRC
Terahertz Generation in Lithium Niobate Driven by Ti:Sapphire Laser Pulses and its Limitations
We experimentally investigate the limits to 800 nm-to-terahertz (THz) energy
conversion in lithium niobate at room temperature driven by amplified
Ti:Sapphire laser pulses with tilted-pulse-front. The influence of the pump
central wavelength, pulse duration, and fluence on THz generation is studied.
We achieved a high peak efficiency of 0.12% using transform limited 150 fs
pulses and observed saturation of the optical to THz conversion efficiency at a
fluence of 15 mJ/cm2. We experimentally identify two main limitations for the
scaling of optical-to-THz conversion efficiencies: (i) the large spectral
broadening of the optical pump spectrum in combination with large angular
dispersion of the tilted-pulse-front and (ii) free-carrier absorption of THz
radiation due to multi-photon absorption of the 800 nm radiation.Comment: 4 pages, 6 figure
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
Well-posedness of boundary layer equations for time-dependent flow of non-Newtonian fluids
We consider the flow of an upper convected Maxwell fluid in the limit of high
Weissenberg and Reynolds number. In this limit, the no-slip condition cannot be
imposed on the solutions. We derive equations for the resulting boundary layer
and prove the well-posedness of these equations. A transformation to Lagrangian
coordinates is crucial in the argument
- …