Explaining the observed velocity dispersion of dwarf galaxies by baryonic mass loss during the first collapse

In the widely adopted LambdaCDM scenario for galaxy formation, dwarf galaxies are the building blocks of larger galaxies. Since they formed at relatively early epochs when the background density was relatively high, they are expected to retain their integrity as satellite galaxies when they merge to form larger entities. Although many dwarf spheroidal galaxies (dSphs) are found in the galactic halo around the Milky Way, their phase space density (or velocity dispersion) appears to be significantly smaller than that expected for satellite dwarf galaxies in the LambdaCDM scenario. In order to account for this discrepancy, we consider the possibility that they may have lost a significant fraction of their baryonic matter content during the first infall at the Hubble expansion turnaround. Such mass loss arises naturally due to the feedback by relatively massive stars which formed in their centers briefly before the maximum contraction. Through a series of N-body simulations, we show that the timely loss of a significant fraction of the dSphs initial baryonic matter content can have profound effects on their asymptotic half-mass radius, velocity dispersion, phase-space density, and the mass fraction between residual baryonic and dark matter.Comment: 6 pages, 6 figures, accepted for publication in the Ap

Electrostatically actuated silicon-based nanomechanical switch at room temperature

We demonstrate a silicon-based high frequency nanomechanical device capable of switching controllably between two states at room temperature. The device uses a nanomechanical resonator with two distinct states in the hysteretic nonlinear regime. In contrast to prior work, we demonstrate room temperature electrostatic actuation and sensing of the switching device with 100% fidelity by phase modulating the drive signal. This phase-modulated device can be used as a low-power high-speed mechanical switch integrated on-chip with silicon circuitry.Comment: 10 pages, 3 figures. Related papers can be found at http://nano.bu.edu

Climate's Long-term Impact on New Zealand Infrastructure (CLINZI) - A Case Study of Hamilton City, New Zealand

Infrastructure systems and services (ISS) are vulnerable to changes in climate. This paper reports on a study of the impact of gradual climate changes on ISS in Hamilton City, New Zealand. This study is unique in that it is the first of its kind to be applied to New Zealand ISS. This study also considers a broader range of ISS than most other climate change studies recently conducted. Using historical climate data and four climate change scenarios, we modelled the impact of climate change on water supply and quality, transport, energy demand, public health and air quality. Our analysis reveals that many of Hamilton City's infrastructure sectors demonstrated greater responsiveness to population changes than changes in gradual climate change. Any future planning decisions should be sensitive to climate change, but not driven by it (even though that may be fashionable to do so). We find there is considerable scope for extending this analysis. First, there is a need for local infrastructure managers to improve the coverage of the data needed for this kind of study. Second, any future study of this kind must focus on daily (rather than monthly) time steps and extreme (as well as gradual) climate changes.Climate change, infrastructure, integrated assessment, adaptation, Agricultural and Food Policy, Community/Rural/Urban Development, Crop Production/Industries, Environmental Economics and Policy, Farm Management, International Relations/Trade, Land Economics/Use, Livestock Production/Industries, Political Economy,

Four-loop quark form factor with quartic fundamental colour factor

We analytically compute the four-loop QCD corrections for the colour structure $(d_F^{abcd})^2$ to the massless non-singlet quark form factor. The computation involves non-trivial non-planar integral families which have master integrals in the top sector. We compute the master integrals by introducing a second mass scale and solving differential equations with respect to the ratio of the two scales. We present details of our calculational procedure. Analytical results for the cusp and collinear anomalous dimensions, and the finite part of the form factor are presented. We also provide analytic results for all master integrals expanded up to weight eight.Comment: 16 pages, 2 figure