3,476 research outputs found
Role of distributed Bragg reflection in photonic-crystal optical waveguides
We show that the properties of the confined modes of a photonic band-gap (PBG) waveguide can be calculated with good accuracy by replacing it with an effective corrugated waveguide that represents only the structure in the vicinity of the middle slab. Such a replacement is helpful in the design of the PBG waveguides as well as in the understanding and analysis of the coupling of different waveguides
Efficient Single Photon Absorption by Optimized Superconducting Nanowire Geometries
We report on simulation results that shows optimum photon absorption by
superconducting nanowires can happen at a fill-factor that is much less than
100%. We also present experimental results on high performance of our
superconducting nanowire single photon detectors realized using NbTiN on
oxidized silicon.Comment: \copyright 2013 IEEE. Submitted to "Numerical Simulation of
Optoelectronic Devices - NUSOD 2013" on 19-April-201
Photonic Crystal Nanobeam Cavity Strongly Coupled to the Feeding Waveguide
A deterministic design of an ultrahigh Q, wavelength scale mode volume
photonic crystal nanobeam cavity is proposed and experimentally demonstrated.
Using this approach, cavities with Q>10^6 and on-resonance transmission T>90%
are designed. The devices fabricated in Si and capped with low-index polymer,
have Q=80,000 and T=73%. This is, to the best of our knowledge, the highest
transmission measured in deterministically designed, wavelength scale high Q
cavities
Transition from stochastic to deterministic behavior in calcium oscillations
Simulation and modeling is becoming more and more important when studying complex biochemical systems. Most often, ordinary differential equations are employed for this purpose. However, these are only applicable when the numbers of participating molecules in the biochemical systems are large enough to be treated as concentrations. For smaller systems, stochastic simulations on discrete particle basis are more accurate. Unfortunately, there are no general rules for determining which method should be employed for exactly which problem to get the most realistic result. Therefore, we study the transition from stochastic to deterministic behavior in a widely studied system, namely the signal transduction via calcium, especially calcium oscillations. We observe that the transition occurs within a range of particle numbers, which roughly corresponds to the number of receptors and channels in the cell, and depends heavily on the attractive properties of the phase space of the respective systems dynamics. We conclude that the attractive properties of a system, expressed, e.g., by the divergence of the system, are a good measure for determining which simulation algorithm is appropriate in terms of speed and realism
Pulling a polymer out of a potential well and the mechanical unzipping of DNA
Motivated by the experiments on DNA under torsion, we consider the problem of
pulling a polymer out of a potential well by a force applied to one of its
ends. If the force is less than a critical value, then the process is activated
and has an activation energy proportinal to the length of the chain. Above this
critical value, the process is barrierless and will occur spontaneously. We use
the Rouse model for the description of the dynamics of the peeling out and
study the average behaviour of the chain, by replacing the random noise by its
mean. The resultant mean-field equation is a nonlinear diffusion equation and
hence rather difficult to analyze. We use physical arguments to convert this in
to a moving boundary value problem, which can then be solved exactly. The
result is that the time required to pull out a polymer of segments
scales like . For models other than the Rouse, we argue that Comment: 11 pages, 6 figures. To appear in PhysicalReview
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