The Dynamical State of Filamentary Infrared Dark Clouds

The dense, cold gas of Infrared Dark Clouds (IRDCs) is thought to be representative of the initial conditions of massive star and star cluster formation. We analyze 13CO(J=1-0) line emission data from the Galactic Ring Survey of Jackson et al. for two filamentary IRDCs, comparing the mass surface densities derived from 13CO, Sigma_13CO, with those derived from mid-infrared small median filter extinction mapping, Sigma_SMF, by Butler & Tan. After accounting for molecular envelopes around the filaments, we find approximately linear relations between Sigma_CO and Sigma_SMF, i.e. an approximately constant ratio Sigma_CO/Sigma_SMF in the clouds. There is a variation of about a factor of two between the two clouds. We find evidence for a modest decrease of Sigma_CO/Sigma_SMF with increasing mass surface density, which may be due to a systematic decrease in temperature, increase in importance of high 13CO opacity cores, increase in dust opacity, or decrease in 13CO abundance due to depletion in regions of higher column density. We perform ellipsoidal and filamentary virial analyses of the clouds, finding that the surface pressure terms are dynamically important and that globally the filaments may not yet have reached virial equilibrium. Some local regions along the filaments appear to be close to virial equilibrium, although still with dynamically important surface pressures, and these appear to be sites where star formation is most active.Comment: 13 pages, accepted to Ap

Evolutionary L∞ identification and model reduction for robust control

An evolutionary approach for modern robust control oriented system identification and model reduction in the frequency domain is proposed. The technique provides both an optimized nominal model and a 'worst-case' additive or multiplicative uncertainty bounding function which is compatible with robust control design methodologies. In addition, the evolutionary approach is applicable to both continuous- and discrete-time systems without the need for linear parametrization or a confined problem domain for deterministic convex optimization. The proposed method is validated against a laboratory multiple-input multiple-output (MIMO) test rig and benchmark problems, which show a higher fitting accuracy and provides a tighter L�¢���� error bound than existing methods in the literature do

Impacts of Ageing Population on Monetary and Exchange Rate Managements in Singapore

This paper finds that the ageing of the population in Singapore will cause a reversal of the current net Central Provident Fund (CPF) contribution into a substantial net CPF withdrawal from 2025, with a peak occurring at 2035. The result is qualitatively robust to changes in the underlying assumptions of the projection. The paper then highlights the implications of this change on the exchange rate and monetary managements in Singapore. First, the Monetary Authority of Singapore (MAS)’s ability to influence Singapore’s exchange rate will be greatly hampered. Second, the net CPF withdrawal will mean sustained liquidity injection into (instead of the usual liquidity drain from) the economy. To avoid unnecessary inflation, the MAS has to find a sustainable way to mob up the excess liquidity due to the sustained liquidity injection. As a simple reversal of MAS’s current foreign exchange market operation will result in substantial shrinkage of foreign reserves, the paper proposes the issuance of government bonds to achieve the dual objectives of mobbing up the excess liquidity and avoiding the shrinkage of foreign reserves. This measure will also help the bond market development in Singapore. Finally, the paper proposes two other measures that can help maintain MAS’s influence on Singapore’s exchange rate to a reasonable level in the longer future.Ageing Population, Central Provident Fund, Exchange Rate System, Monetary Policy, Singapore.

Stray field signatures of N\'eel textured skyrmions in Ir/Fe/Co/Pt multilayer films

Skyrmions are nanoscale spin configurations with topological properties that hold great promise for spintronic devices. Here, we establish their N\'eel texture, helicity, and size in Ir/Fe/Co/Pt multilayer films by constructing a multipole expansion to model their stray field signatures and applying it to magnetic force microscopy (MFM) images. Furthermore, the demonstrated sensitivity to inhomogeneity in skyrmion properties, coupled with a unique capability to estimate the pinning force governing dynamics, portends broad applicability in the burgeoning field of topological spin textures.Comment: 6 pages, 4 figures, significantly revised and upgraded. For the updated supplementary material please contact one of the corresponding author

The Chiral Extension of Lattice QCD

The chiral extension of Quantum Chromodynamics (XQCD) adds to the standard lattice action explicit pseudoscalar meson fields for the chiral condensates. With this action, it is feasible to do simulations at the chiral limit with zero mass Goldstone modes. We review the arguments for why this is expected to be in the same universality class as the traditional action. We present preliminary results on convergence of XQCD for naive fermions and on the methodology for introducing counter terms to restore chiral symmetry for Wilson fermions.Comment: 7 pages, LATTICE 94 talk by R. Brower: Latex file with 2 postscript figures for encapsulatio