Foerster resonance energy transfer rate and local density of optical states are uncorrelated in any dielectric nanophotonic medium

Motivated by the ongoing debate about nanophotonic control of Foerster resonance energy transfer (FRET), notably by the local density of optical states (LDOS), we study an analytic model system wherein a pair of ideal dipole emitters - donor and acceptor - exhibit energy transfer in the vicinity of an ideal mirror. The FRET rate is controlled by the mirror up to distances comparable to the donor-acceptor distance, that is, the few-nanometer range. For vanishing distance, we find a complete inhibition or a four-fold enhancement, depending on dipole orientation. For mirror distances on the wavelength scale, where the well-known `Drexhage' modification of the spontaneous-emission rate occurs, the FRET rate is constant. Hence there is no correlation between the Foerster (or total) energy transfer rate and the LDOS. At any distance to the mirror, the total energy transfer between a closely-spaced donor and acceptor is dominated by Foerster transfer, i.e., by the static dipole-dipole interaction that yields the characteristic inverse-sixth-power donor-acceptor distance dependence in homogeneous media. Generalizing to arbitrary inhomogeneous media with weak dispersion and weak absorption in the frequency overlap range of donor and acceptor, we derive two main theoretical results. Firstly, the spatially dependent Foerster energy transfer rate does not depend on frequency, hence not on the LDOS. Secondly the FRET rate is expressed as a frequency integral of the imaginary part of the Green function. This leads to an approximate FRET rate in terms of the LDOS integrated over a huge bandwidth from zero frequency to about 10 times the donor emission frequency, corresponding to the vacuum-ultraviolet. Even then, the broadband LDOS hardly contributes to the energy transfer rates. We discuss practical consequences including quantum information processing.Comment: 17 pages, 9 figure

Equine digital tendons show breed‐specific differences in their mechanical properties that may relate to athletic ability and predisposition to injury

Background Throughout the ages, human subjects have selected horse breeds for their locomotor capacities. Concurrently, tissue properties may have diversified because of specific requirements of different disciplines. Objectives The aim of this study was to compare the biomechanical properties of tendons with different functions between equine breeds traditionally selected for racing or sport. Study design This study used ex vivo tendons and compared the mechanical properties of the common digital extensor tendon (CDET) and superficial digital flexor tendon (SDFT) between racehorses (Thoroughbred [TB]) and sports horses (Friesian Horse [FH], Warmblood [WB]). Methods The SDFT and CDET of FH (n = 12), WBs (n = 12) and TBs (n = 8) aged 3-12 years were harvested. The cross sectional area (cm(2)), maximal load (N), ultimate strain (%), ultimate stress (MPa) and elastic modulus (MPa) were determined and tested for significant differences between the breeds (P<0.05). Results The SDFT from WB horses had a significantly lower elastic modulus than TB horses and failed at a higher strain and load than both FHs and TBs. The mechanical properties of the CDET did not differ between breeds. In agreement with previous studies, the CDET failed at a higher stress and had a higher elastic modulus than the SDFT and, for the WB group of horses only, failed at a significantly lower strain. Interestingly, the mode of failure differed between breeds, particularly with respect to the FHs. Main limitations The exercise history of horses used in this study was unknown and the age-range was relatively large; both these factors may have influenced the absolute properties reported in this study. Conclusions This study shows for the first time that mechanical properties of the SDFT differ between breeds. These properties are likely to be related to selection for high-speed vs. an extravagant elastic gait and may be an important indicator of performance ability. The is available in Spanish - see Supporting Informatio

Optimal control of light propagation through multiple-scattering media in the presence of noise

We study the control of coherent light propagation through multiple-scattering media in the presence of measurement noise. In our experiments, we use a two-step optimization procedure to find the optimal incident wavefront. We conclude that the degree of optimal control of coherent light propagation through a multiple-scattering medium is only determined by the number of photoelectrons detected per single speckle spot. The prediction of our model agrees well with the experimental results. Our results offer opportunities for imaging applications through scattering media such as biological tissue in the shot noise limit

Light propagation and emission in complex photonic media

We provide an introduction to complex photonic media, that is, composite materials with spatial inhomogeneities that are distributed over length scales comparable to or smaller than the wavelength of light. This blossoming field is firmly rooted in condensed matter physics, in optics, and in materials science. Many stimulating analogies exist with other wave phenomena such as sound and seismology, X-rays, neutrons. The field has a rich history, which has led to many applications in lighting, novel lasers, light harvesting, microscopy, and bio optics. We provide a brief overview of complex photonic media with different classes of spatial order, varying from completely random to long-periodically ordered structures, quasi crystalline and aperiodic structures, and arrays of cavities. In addition to shaping optical waves by suitable photonic nanostructures, the realization is quickly arising that the spatial shaping of optical wavefronts with spatial light modulators dramatically increases the number of control parameters. As a result, it is becoming possible for instance to literally see through completely opaque complex media. We discuss a unified view of complex photonic media by means of a photonic interaction strength parameter. This parameter gauges the interaction of light with any complex photonic medium, and allows to compare complex media from different classes for similar applications.Comment: 8 pages, 2 figures, Light Localisation and Lasing: Random and Quasi-Random Photonic Structures, Eds. M. Ghulinyan and L. Pavesi, (Cambridge Univ. Press, Cambridge, 2015) Ch. 1, p.

Discretionary monetary policy in the Calvo model

We study discretionary equilibrium in the Calvo pricing model for a monetary authority that chooses the money supply. The steady-state inflation rate is above eight percent for a baseline calibration, and it varies non-monotonically with the degree of price stickiness. If the initial condition involves inflation higher than steady state, discretionary policy generates an immediate drop in inflation followed by a gradual increase to the steady state. Unlike the two-period Taylor model, discretionary policy in the Calvo model does not accommodate predetermined prices in a way that inevitably leads to multiple private-sector equilibria.

Design of a 3D photonic band gap cavity in a diamond-like inverse woodpile photonic crystal

We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamond-like crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centred on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell bandstructure calculations with up to $5 \times 5 \times 5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centred on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 $\lambda^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donor-like resonances appear for smaller defect radius, whereas no acceptor-like resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in non-inverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.Comment: 11 figure