Modelling and device simulation of photonic crystal surface emitting lasers based on modal index analysis

We present a novel semi-analytical method utilising modal index analysis, for modelling the field resonances of photonic crystal surface emitting lasers (PCSELs). This method shows very good agreement with other modelling techniques in terms of mode calculations, with the added advantages of computational simplicity, the calculation of threshold gain, and rapid analysis of finite structures. We are able to model the effect of external lateral feedback and simulations indicate that the near-field peak can be electronically displaced and the threshold as well as the frequency can be controlled through external in-plane feedback, paving the way to dynamic control of PCSELs

Coherently coupled photonic-crystal surface-emitting laser array

The realization of a 1 × 2 coherently coupled photonic crystal surface emitting laser array is reported. New routes to power scaling are discussed and the electronic control of coherence is demonstrated

TCTAP A-046 Comparison of Two-and Three-dimensional Quantitative Coronary Angiography to Intravascular Ultrasound in the Assessment of Left Main Bifurcation Lesions

Sexual transmission is the primary route of HIV-1 infection, and DC subsets are thought to be involved in viral dissemination to T cells. In the genital mucosa, two main subsets of DCs are present: epithelial LCs capture and degrade HIV-1 through C-type lectin Langerin, whereas subepithelial DCs express DC-SIGN, which facilitates HIV-1 transmission to T cells. As there is currently no HIV-1 vaccine availab

Evaluation of true maximal oxygen uptake based on a novel set of standardized criteria

In this study, criteria are used to identify whether a subject has elicited maximal oxygen uptake. We evaluated the validity of traditional maximal oxygen uptake criteria and propose a novel set of criteria. Twenty athletes completed a maximal oxygen uptake test, consisting of an incremental phase and a subsequent supramaximal phase to exhaustion (verification phase). Traditional and novel maximal oxygen uptake criteria were evaluated. Novel criteria were: oxygen uptake plateau defined as the difference between modelled and actual maximal oxygen uptake >50% of the regression slope of the individual oxygen uptake-workrate relationship; as in the first criterion, but for maximal verification oxygen uptake; and a difference of [less than or equal to]4 beats x [min.sup.-1] between maximal heart rate values in the 2 phases. Satisfying the traditional oxygen uptake plateau criterion was largely an artefact of the between-subject variation in the oxygen uptake-workrate relationship. Secondary criteria, supposedly an indicator of maximal effort, were often satisfied long before volitional exhaustion, even at intensities as low as 61% maximal oxygen uptake. No significant mean differences were observed between the incremental and verification phases for oxygen uptake (t = 0.4; p = 0.7) or heart rate (t = 0.8; p = 0.5). The novel oxygen uptake plateau criterion, maximal oxygen uptake verification criterion, and maximal heart rate verification criterion were satisfied by 17, 18, and 18 subjects, respectively. The small individual absolute differences in oxygen uptake between incremental and verification phases observed in most subjects provided additional confidence that maximal oxygen uptake was elicited. Current maximal oxygen uptake criteria were not valid and novel criteria should be further explored

Strong Universality in Forced and Decaying Turbulence

The weak version of universality in turbulence refers to the independence of the scaling exponents of the $n$th order strcuture functions from the statistics of the forcing. The strong version includes universality of the coefficients of the structure functions in the isotropic sector, once normalized by the mean energy flux. We demonstrate that shell models of turbulence exhibit strong universality for both forced and decaying turbulence. The exponents {\em and} the normalized coefficients are time independent in decaying turbulence, forcing independent in forced turbulence, and equal for decaying and forced turbulence. We conjecture that this is also the case for Navier-Stokes turbulence.Comment: RevTex 4, 10 pages, 5 Figures (included), 1 Table; PRE, submitte

Structure and phase-composition of Ti-doped gas atomized Raney-type Ni catalyst precursor alloys

Raney-type Ni precursor alloys containing 75 at.% Al and doped with 0, 0.75, 1.5 and 3.0 at.% Ti have been produced by a gas atomization process. The resulting powders have been classified by size fraction with subsequent investigation by powder XRD, SEM and EDX analysis. The undoped powders contain, as expected, the phases Ni2Al3, NiAl3 and an Al-eutectic. The Ti-doped powders contain an additional phase with the TiAl3 DO22 crystal structure. However, quantitative analysis of the XRD results indicate a far greater fraction of the TiAl3 phase is present than could be accounted for by a simple mass balance on Ti. This appears to be a (TixNi1-x)Al3 phase in which higher cooling rates favour small x (low Ti-site occupancy by Ti atoms). SEM and EDX analysis reveal that virtually all the available Ti is contained within the TiAl3 phase, with negligible Ti dissolved in either the Ni2Al3 or NiAl3 phases

The Flare-energy Distributions Generated by Kink-unstable Ensembles of Zero-net-current Coronal Loops

It has been proposed that the million degree temperature of the corona is due to the combined effect of barely-detectable energy releases, so called nanoflares, that occur throughout the solar atmosphere. Alas, the nanoflare density and brightness implied by this hypothesis means that conclusive verification is beyond present observational abilities. Nevertheless, we investigate the plausibility of the nanoflare hypothesis by constructing a magnetohydrodynamic (MHD) model that can derive the energy of a nanoflare from the nature of an ideal kink instability. The set of energy-releasing instabilities is captured by an instability threshold for linear kink modes. Each point on the threshold is associated with a unique energy release and so we can predict a distribution of nanoflare energies. When the linear instability threshold is crossed, the instability enters a nonlinear phase as it is driven by current sheet reconnection. As the ensuing flare erupts and declines, the field transitions to a lower energy state, which is modelled by relaxation theory, i.e., helicity is conserved and the ratio of current to field becomes invariant within the loop. We apply the model so that all the loops within an ensemble achieve instability followed by energy-releasing relaxation. The result is a nanoflare energy distribution. Furthermore, we produce different distributions by varying the loop aspect ratio, the nature of the path to instability taken by each loop and also the level of radial expansion that may accompany loop relaxation. The heating rate obtained is just sufficient for coronal heating. In addition, we also show that kink instability cannot be associated with a critical magnetic twist value for every point along the instability threshold

Three-dimensional finite-difference time-domain modelling of photonic crystal surface-emitting lasers

We investigate the beam divergence in far-field region, diffraction loss and optical confinement factors of all-semiconductor and void-semiconductor photonic-crystal surface-emitting lasers (PCSELs), containing either InGaP/GaAs or InGaP/air photonic crystals using a three-dimensional FDTD model. We explore the impact of changing the PC hole shape, size, and lattice structure in addition to the choice of all-semiconductor or void-semiconductor designs. We discuss the determination of the threshold gain from the diffraction losses, and explore limitations to direct modulation of the PCSEL. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Infrared exponents and the strong-coupling limit in lattice Landau gauge

We study the gluon and ghost propagators of lattice Landau gauge in the strong-coupling limit beta=0 in pure SU(2) lattice gauge theory to find evidence of the conformal infrared behavior of these propagators as predicted by a variety of functional continuum methods for asymptotically small momenta $q^2 \ll \Lambda_\mathrm{QCD}^2$. In the strong-coupling limit, this same behavior is obtained for the larger values of a^2q^2 (in units of the lattice spacing a), where it is otherwise swamped by the gauge field dynamics. Deviations for a^2q^2 < 1 are well parameterized by a transverse gluon mass $\propto 1/a$. Perhaps unexpectedly, these deviations are thus no finite-volume effect but persist in the infinite-volume limit. They furthermore depend on the definition of gauge fields on the lattice, while the asymptotic conformal behavior does not. We also comment on a misinterpretation of our results by Cucchieri and Mendes in Phys. Rev. D81 (2010) 016005.Comment: 17 pages, 12 figures. Revised version (mainly sections I and II); references and comments on subsequent work on the subject added

Strong-coupling study of the Gribov ambiguity in lattice Landau gauge

We study the strong-coupling limit beta=0 of lattice SU(2) Landau gauge Yang-Mills theory. In this limit the lattice spacing is infinite, and thus all momenta in physical units are infinitesimally small. Hence, the infrared behavior can be assessed at sufficiently large lattice momenta. Our results show that at the lattice volumes used here, the Gribov ambiguity has an enormous effect on the ghost propagator in all dimensions. This underlines the severity of the Gribov problem and calls for refined studies also at finite beta. In turn, the gluon propagator only mildly depends on the Gribov ambiguity.Comment: 14 pages, 22 figures; minor changes, matches version to appear in Eur. Phys. J.