Beyond simulation: designing for uncertainty and robust solutions

Simulation is an increasingly essential tool in the design of our environment, but any model is only as good as the initial assumptions on which it is built. This paper aims to outline some of the limits and potential dangers of reliance on simulation, and suggests how to make our models, and our buildings, more robust with respect to the uncertainty we face in design. It argues that the single analyses provided by most simulations display too precise and too narrow a result to be maximally useful in design, and instead a broader description is required, as might be provided by many differing simulations. Increased computing power now allows this in many areas. Suggestions are made for the further development of simulation tools for design, in that these increased resources should be dedicated not simply to the accuracy of single solutions, but to a bigger picture that takes account of a design’s robustness to change, multiple phenomena that cannot be predicted, and the wider range of possible solutions. Methods for doing so, including statistical methods, adaptive modelling, machine learning and pattern recognition algorithms for identifying persistent structures in models, will be identified. We propose a number of avenues for future research and how these fit into design process, particularly in the case of the design of very large buildings

Line-of-sight velocity distributions of elliptical galaxies from collisionless mergers

We analyse the skewness of the line-of-sight velocity distributions in model elliptical galaxies built through collisionless galaxy mergers. We build the models using large N-body simulations of mergers between either two spiral or two elliptical galaxies. Our aim is to investigate whether the observed ranges of skewness coefficient (h3) and the rotational support (V/sigma), as well as the anticorrelation between h3 and V, may be reproduced through collisionless mergers. Previous attempts using N-body simulations failed to reach V/sigma ~ 1-2 and corresponding high h3 values, which suggested that gas dynamics and ensuing star formation might be needed in order to explain the skewness properties of ellipticals through mergers. Here we show that high V/sigma and high h3 are reproduced in collisionless spiral-spiral mergers whenever a central bulge allows the discs to retain some of their original angular momentum during the merger. We also show that elliptical-elliptical mergers, unless merging from a high-angular momentum orbit, reproduce the strong skewness observed in non-rotating, giant, boxy ellipticals. The behaviour of the h3 coefficient therefore associates rapidly-rotating disky ellipticals to disc-disc mergers, and associates boxy, slowly-rotating giant ellipticals to elliptical-elliptical mergers, a framework generally consistent with the expectations of hierarchical galaxy formation.Comment: 5 pages, 4 figures, MNRAS Letters, in pres

A phenomenological analysis of azimuthal asymmetries in unpolarized semi-inclusive deep inelastic scattering

We present a phenomenological analysis of the cos-phi and cos-2phi asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on the recent multidimensional data released by the COMPASS and HERMES Collaborations. In the TMD framework, valid at relatively low transverse momenta, these asymmetries arise from intrinsic transverse momentum and transverse spin effects, and from their correlations. The role of the Cahn and Boer-Mulders effects in both azimuthal moments is explored up to order 1/Q. As the kinematics of the present experiments is dominated by the low-Q^2 region, higher-twist contributions turn out to be important, affecting the results of our fits.Comment: 18 pages, 5 figures, one paragraph added at the end of Section IV, one reference added. PRD versio

The properties of attractors of canalyzing random Boolean networks

We study critical random Boolean networks with two inputs per node that contain only canalyzing functions. We present a phenomenological theory that explains how a frozen core of nodes that are frozen on all attractors arises. This theory leads to an intuitive understanding of the system's dynamics as it demonstrates the analogy between standard random Boolean networks and networks with canalyzing functions only. It reproduces correctly the scaling of the number of nonfrozen nodes with system size. We then investigate numerically attractor lengths and numbers, and explain the findings in terms of the properties of relevant components. In particular we show that canalyzing networks can contain very long attractors, albeit they occur less often than in standard networks.Comment: 9 pages, 8 figure

Modelling the relative velocities of isolated pairs of galaxies

We study the comoving relative velocities, v12, of model isolated galaxy pairs at z=0.5. For this purpose, we use the predictions from the GALFORM semi-analytical model of galaxy formation and evolution based on a Lambda cold dark matter cosmology consistent with the results from WMAP7. In real space, we find that isolated pairs of galaxies are predicted to form an angle t with the line-of-sight that is uniformily distributed as expected if the Universe is homogeneous and isotropic. We also find that isolated pairs of galaxies separated by a comoving distance between 1 and 3 Mpc/h are predicted to have =0. For galaxies in this regime, the distribution of the angle t is predicted to change minimally from real to redshift space, with a change smaller than 5% in . However, the distances defining the comoving regime strongly depends on the applied isolation criteria.Comment: 4 pages, 4 figures, SF2A 2013 Proceedin

How to reduce the suspension thermal noise in LIGO without improving the Q's of the pendulum and violin modes

The suspension noise in interferometric gravitational wave detectors is caused by losses at the top and the bottom attachments of each suspension fiber. We use the Fluctuation-Dissipation theorem to argue that by careful positioning of the laser beam spot on the mirror face it is possible to reduce the contribution of the bottom attachment point to the suspension noise by several orders of magnitude. For example, for the initial and enhanced LIGO design parameters (i.e. mirror masses and sizes, and suspension fibers' lengths and diameters) we predict a reduction of $\sim 100$ in the "bottom" spectral density throughout the band $35-100\hbox{Hz}$ of serious thermal noise. We then propose a readout scheme which suppresses the suspension noise contribution of the top attachment point. The idea is to monitor an averaged horizontal displacement of the fiber of length $l$; this allows one to record the contribution of the top attachment point to the suspension noise, and later subtract it it from the interferometer readout. For enhanced LIGO this would allow a suppression factor about 100 in spectral density of suspension thermal noise.Comment: a few misprints corrected; submitted to Classical and Quantum Gravit

Solar System experiments do not yet veto modified gravity models

The dynamical equivalence between modified and scalar-tensor gravity theories is revisited and it is concluded that it breaks down in the limit to general relativity. A gauge-independent analysis of cosmological perturbations in both classes of theories lends independent support to this conclusion. As a consequence, the PPN formalism of scalar-tensor gravity and Solar System experiments do not veto modified gravity, as previously thought.Comment: 7 pages, latex, submitted to Phys. Rev.

The Calcium Triplet metallicity calibration for galactic bulge stars

We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially suited for solar and supersolar metallicity giants, typical of external massive galaxies. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R~20,000 and at R~6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines, deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 A. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second order correction, based on literature globular cluster data, we derived the unique calibration equation [Fe/H]$_{CaT} = -3.150 + 0.432W' + 0.006W'^2$, with a rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3<[Fe/H]<+0.7.Comment: Accepted for publication in A&