A comparison of two closely-related approaches to aerodynamic design optimization

Two related methods for aerodynamic design optimization are compared. The methods, called the implicit gradient approach and the variational (or optimal control) approach, both attempt to obtain gradients necessary for numerical optimization at a cost significantly less than that of the usual black-box approach that employs finite difference gradients. While the two methods are seemingly quite different, they are shown to differ (essentially) in that the order of discretizing the continuous problem, and of applying calculus, is interchanged. Under certain circumstances, the two methods turn out to be identical. We explore the relationship between these methods by applying them to a model problem for duct flow that has many features in common with transonic flow over an airfoil. We find that the gradients computed by the variational method can sometimes be sufficiently inaccurate to cause the optimization to fail

A note on the effect of post-mortem maturation on colour of bovine Longissimus dorsi muscle

peer-reviewedFinancial support to P.G. Dunne was provided under the Walsh Fellowship programme of Teagasc.Fifteen heifers were housed and fed a concentrate diet while 54 counterparts grazed at pasture for 90 days at which stage six heifers from each group were slaughtered. The remaining animals in the pasture group were then housed and offered either: concentrate only; concentrate plus grass silage with silage accounting for either 20% or 50% of the total dry matter offered; or zero-grazed grass plus concentrate with grass accounting for 83% of the dry matter offered. Heifers (3/diet) were slaughtered 28, 56, 91 and 120 days thereafter. Colour characteristics of M. longissimus dorsi (LD) were measured at 48 h post mortem. The LD was then vacuum-packaged and stored at between 0 and 4 °C in darkness for 12 days, when colour characteristics were again measured. Maturation of LD resulted in meat that had higher redness values (‘a’ value; P<0.001) and a more intense red colour (higher ‘C’ value; P<0.001) at 14 days post mortem than at 2 days, regardless of diet/duration of feeding. Maturation also resulted in a brighter colour (higher ‘L’ value; P<0.001) but this difference was greatest when cattle were slaughtered the day-56 time point

The Near Infrared Background: Interplanetary Dust or Primordial Stars?

The intensity of the diffuse ~ 1 - 4 micron sky emission from which solar system and Galactic foregrounds have been subtracted is in excess of that expected from energy released by galaxies and stars that formed during the z < 5 redshift interval (Arendt & Dwek 2003, Matsumoto et al. 2005). The spectral signature of this excess near-infrared background light (NIRBL) component is almost identical to that of reflected sunlight from the interplanetary dust cloud, and could therefore be the result of the incomplete subtraction of this foreground emission component from the diffuse sky maps. Alternatively, this emission component could be extragalactic. Its spectral signature is consistent with that of redshifted continuum and recombination line emission from HII regions formed by the first generation of very massive stars. In this paper we analyze the implications of this spectral component for the formation rate of these Population III stars, the redshift interval during which they formed, the reionization of the universe and evolution of collapsed halo masses. We find that to reproduce the intensity and spectral shape of the NIRBL requires a peak star formation rate that is higher by about a factor of 4 to 10 compared to those derived from hierarchical models. Furthermore, an extragalactic origin for the NIRBL leads to physically unrealistic absorption-corrected spectra of distant TeV blazars. All these results suggest that Pop III stars contribute only a fraction of the NIRBL intensity with zodiacal light, star forming galaxies, and/or non-nuclear sources giving rise to the remaining fraction.Comment: 28 pages including 7 embedded figures. Submitted to Ap

Gravitational Correction to Running of Gauge Couplings

We calculate the contribution of graviton exchange to the running of gauge couplings at lowest non-trivial order in perturbation theory. Including this contribution in a theory that features coupling constant unification does not upset this unification, but rather shifts the unification scale. When extrapolated formally, the gravitational correction renders all gauge couplings asymptotically free.Comment: 4 pages, 2 figures; v2: Clarified awkward sentences and notations. Corrected typos. Added references and discussion thereof in introduction. Minor copy editting changes to agree with version to be published in Physical Review Letter

Characterization and stability of a fermionic \nu=1/3 fractional Chern insulator

Using the infinite density matrix renormalization group method on an infinite cylinder geometry, we characterize the $1/3$ fractional Chern insulator state in the Haldane honeycomb lattice model at $\nu=1/3$ filling of the lowest band and check its stability. We investigate the chiral and topological properties of this state through (i) its Hall conductivity, (ii) the topological entanglement entropy, (iii) the $U(1)$ charge spectral flow of the many body entanglement spectrum, and (iv) the charge of the anyons. In contrast to numerical methods restricted to small finite sizes, the infinite cylinder geometry allows us to access and characterize directly the metal to fractional Chern insulator transition. We find indications it is first order and no evidence of other competing phases. Since our approach does not rely on any band or subspace projection, we are able to prove the stability of the fractional state in the presence of interactions exceeding the band gap, as has been suggested in the literature. As a by-product we discuss the signatures of Chern insulators within this technique.Comment: published versio

Nonequilibrium static growing length scales in supercooled liquids on approaching the glass transition

The small wavenumber $k$ behavior of the structure factor $S(k)$ of overcompressed amorphous hard-sphere configurations was previously studied for a wide range of densities up to the maximally random jammed state, which can be viewed as a prototypical glassy state [A. Hopkins, F. H. Stillinger and S. Torquato, Phys. Rev. E, 86, 021505 (2012)]. It was found that a precursor to the glassy jammed state was evident long before the jamming density was reached as measured by a growing nonequilibrium length scale extracted from the volume integral of the direct correlation function $c(r)$, which becomes long-ranged as the critical jammed state is reached. The present study extends that work by investigating via computer simulations two different atomic models: the single-component Z2 Dzugutov potential in three dimensions and the binary-mixture Kob-Andersen potential in two dimensions. Consistent with the aforementioned hard-sphere study, we demonstrate that for both models a signature of the glass transition is apparent well before the transition temperature is reached as measured by the length scale determined from from the volume integral of the direct correlation function in the single-component case and a generalized direct correlation function in the binary-mixture case. The latter quantity is obtained from a generalized Orstein-Zernike integral equation for a certain decoration of the atomic point configuration. We also show that these growing length scales, which are a consequence of the long-range nature of the direct correlation functions, are intrinsically nonequilibrium in nature as determined by an index $X$ that is a measure of deviation from thermal equilibrium. It is also demonstrated that this nonequilibrium index, which increases upon supercooling, is correlated with a characteristic relaxation time scale.Comment: 26 pages, 14 figure

Do methanethiol adsorbates on the Au(111) surface dissociate?

The interaction of methanethiol molecules CH$_{3}$SH with the Au(111) surface is investigated, and it is found for the first time that the S-H bond remains intact when the methanethiol molecules are adsorbed on the regular Au(111) surface. However, it breaks if defects are present in the Au(111) surface. At low coverage, the fcc region is favored for S atom adsorption, but at saturated coverage the adsorption energies at various sites are almost iso-energetic. The presented calculations show that a methanethiol layer on the regular Au(111) surface does not dimerize.Comment: 4 pages, 2 figures, 4 tables, submitted to Phys. Rev. Let

Computational probes of molecular motion in the Lewis and Whanstrom model for ortho-terphenyl

We use molecular dynamics simulations to investigate translational and rotational diffusion in a rigid three-site model of the fragile glass former ortho-terphenyl, at 260 K < T < 346 K and ambient pressure. An Einstein formulation of rotational motion is presented, which supplements the commonly-used Debye model. The latter is shown to break down at supercooled temperatures as the mechanism of molecular reorientation changes from small random steps to large infrequent orientational jumps. We find that the model system exhibits non-Gaussian behavior in translational and rotational motion, which strengthens upon supercooling. Examination of particle mobility reveals spatially heterogeneous dynamics in translation and rotation, with a strong spatial correlation between translationally and rotationally mobile particles. Application of the Einstein formalism to the analysis of translation-rotation decoupling results in a trend opposite to that seen in conventional approaches based on the Debye formalism, namely an enhancement in the effective rate of rotational motion relative to translation upon supercooling.Comment: 11 pages, 8 figures, 1 tabl