11,813 research outputs found
The covering radius problem for sets of perfect matchings
Consider the family of all perfect matchings of the complete graph
with vertices. Given any collection of perfect matchings of
size , there exists a maximum number such that if ,
then there exists a perfect matching that agrees with each perfect matching in
in at most edges. We use probabilistic arguments to give
several lower bounds for . We also apply the Lov\'asz local lemma to
find a function such that if each edge appears at most times
then there exists a perfect matching that agrees with each perfect matching in
in at most edges. This is an analogue of an extremal result
vis-\'a-vis the covering radius of sets of permutations, which was studied by
Cameron and Wanless (cf. \cite{cameron}), and Keevash and Ku (cf. \cite{ku}).
We also conclude with a conjecture of a more general problem in hypergraph
matchings.Comment: 10 page
Numerical optimization techniques for bound circulation distribution for minimum induced drag of Nonplanar wings: Computer program documentation
A two dimensional advanced panel far-field potential flow model of the undistorted, interacting wakes of multiple lifting surfaces was developed which allows the determination of the spanwise bound circulation distribution required for minimum induced drag. This model was implemented in a FORTRAN computer program, the use of which is documented in this report. The nonplanar wakes are broken up into variable sized, flat panels, as chosen by the user. The wake vortex sheet strength is assumed to vary linearly over each of these panels, resulting in a quadratic variation of bound circulation. Panels are infinite in the streamwise direction. The theory is briefly summarized herein; sample results are given for multiple, nonplanar, lifting surfaces, and the use of the computer program is detailed in the appendixes
A method of solving sets of nonlinear algebraic equations Progress report
Methods for solving nonlinear algebraic equations in computer programs for nuclear magnetic resonance spectroscop
Suppression of Landau damping via electron band gap
The pondermotive potential in the X-ray Raman compression can generate an
electron band gap which suppresses the Landau damping. The regime is identified
where a Langmuir wave can be driven without damping in the stimulated Raman
compression. It is shown that the partial wave breaking and the frequency
detuning due to the trapped particles would be greatly reduced.Comment: 4 pages, 5 figure
Development of polymer network of phenolic and epoxies resins mixed with linseed oil: pilot study
Epoxy resin was mixed with phenolic resins in different percentages by weight. Composite 40/60 means the proportion by weight of epoxy resin is 40 percent. It was found that only composites 50/50 and 40/60 could be cured in ambient conditions. Dynamic mechanical analysis showed that only these two composites form interpenetrating polymer network. The addition of linseed oil to the two resins results also in the formation of interpenetrating network irrespective of proportion by weight of the resins; the mechanical properties will only be better when the percentage by weight of epoxy resin is higher; the aim of reducing cost and at the same time maintaining the mechanical properties cannot be fully achieved because epoxy resin is much more expensive than its counterpart
Backward Raman compression of x-rays in metals and warm dense matters
Experimentally observed decay rate of the long wavelength Langmuir wave in
metals and dense plasmas is orders of magnitude larger than the prediction of
the prevalent Landau damping theory. The discrepancy is explored, and the
existence of a regime where the forward Raman scattering is stable and the
backward Raman scattering is unstable is examined. The amplification of an
x-ray pulse in this regime, via the backward Raman compression, is
computationally demonstrated, and the optimal pulse duration and intensity is
estimated.Comment: 4 pages, 3 figures, submitted to PR
Weak phase stiffness and mass divergence of superfluid in underdoped cuprates
Despite more than two decades of intensive investigations, the true nature of
high temperature (high-) superconductivity observed in the cuprates
remains elusive to the researchers. In particular, in the so-called
`underdoped' region, the overall behavior of superconductivity deviates
from the standard theoretical description pioneered by Bardeen,
Cooper and Schrieffer (BCS). Recently, the importance of phase fluctuation of
the superconducting order parameter has gained significant support from various
experiments. However, the microscopic mechanism responsible for the
surprisingly soft phase remains one of the most important unsolved puzzles.
Here, opposite to the standard BCS starting point, we propose a simple,
solvable low-energy model in the strong coupling limit, which maps the
superconductivity literally into a well-understood physics of superfluid in a
special dilute bosonic system of local pairs of doped holes. In the
prototypical material (LaSr)CuO, without use of
any free parameter, a -wave superconductivity is obtained for doping above
, below which unexpected incoherent -wave pairs dominate.
Throughout the whole underdoped region, very soft phases are found to originate
from enormous mass enhancement of the pairs. Furthermore, a striking mass
divergence is predicted that dictates the occurrence of the observed quantum
critical point. Our model produces properties of the superfluid in good
agreement with the experiments, and provides new insights into several current
puzzles. Owing to its simplicity, this model offers a paradigm of great value
in answering the long-standing challenges in underdoped cuprates
Inverter-Based Low-Voltage CCII- Design and Its Filter Application
This paper presents a negative type second-generation current conveyor (CCII-). It is based on an inverter-based low-voltage error amplifier, and a negative current mirror. The CCII- could be operated in a very low supply voltage such as ±0.5V. The proposed CCII- has wide input voltage range (±0.24V), wide output voltage (±0.24V) and wide output current range (±24mA). The proposed CCII- has no on-chip capacitors, so it can be designed with standard CMOS digital processes. Moreover, the architecture of the proposed circuit without cascoded MOSFET transistors is easily designed and suitable for low-voltage operation. The proposed CCII- has been fabricated in TSMC 0.18μm CMOS processes and it occupies 1189.91 x 1178.43μm2 (include PADs). It can also be validated by low voltage CCII filters
Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O
We report an unusual persistence of superconductivity against high magnetic
fields in the iron chalcogenide film FeTe:O below ~ 2.5 K. Instead of
saturating like a mean-field behavior with a single order parameter, the
measured low-temperature upper critical field increases progressively,
suggesting a large supply of superconducting states accessible via magnetic
field or low-energy thermal fluctuations. We demonstrate that superconducting
states of finite momenta can be realized within the conventional theory,
despite its questionable applicability. Our findings reveal a fundamental
characteristic of superconductivity and electronic structure in the
strongly-correlated iron-based superconductors.Comment: 10 pages, 3 figure
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