8th Massachusetts : March & Two Step

https://digitalcommons.library.umaine.edu/mmb-ps/2449/thumbnail.jp

A Conversation between Milner Ball and James Boyd White

The editors of the Journal invited me to review James Boyd White\u27s Acts of Hope. In response I proposed inviting Professor White to join me in a conversation about his work. First the editors and then he accepted the proposal. Professor White and I agreed that we might call a halt to this experiment at any time because we would not subvert our friendship in the attempt to enact an instance of it in print. The editors accepted the risk that we might at last have no pages for them. - MS

Lou\u27siana Blues

https://digitalcommons.library.umaine.edu/mmb-vp/2032/thumbnail.jp

Halo Substructure and the Power Spectrum

In this proceeding, we present the results of a semi-analytic study of CDM substructure as a function of the primordial power spectrum. We apply our method to several tilted models in the LCDM framework with n=0.85-1.1, sigma_8=0.65-1.2 when COBE normalized. We also study a more extreme, warm dark matter-like spectrum that is sharply truncated below a scale of 10^10 h^-1 Msun. We show that the mass fraction of halo substructure is not a strong function of spectral slope, so it likely will be difficult to constrain tilt using flux ratios of gravitationally lensed quasars. On the positive side, all of our CDM-type models yield projected mass fractions in good agreement with strong lensing estimates: f \sim 1.5% at M \sim 10^8 Msun. The truncated model produces a significantly smaller fraction, f \lsim 0.3%, suggesting that warm dark matter-like spectra may be distinguished from CDM spectra using lensing. We also discuss the issue of dwarf satellite abundances, with emphasis on the cosmological dependence of the map between the observed central velocity dispersion of Milky Way satellites and the maximum circular velocities of their host halos. In agreement with earlier work, we find that standard LCDM over-predicts the estimated count of Milky Way satellites at fixed Vmax by an order of magnitude, but tilted models do better because subhalos are less concentrated. Interestingly, under the assumption that dwarfs have isotropic velocity dispersion tensors, models with significantly tilted spectra (n \lsim 0.85, sigma_8 \lsim 0.7) may under-predict the number of large Milky Way satellites with Vmax \gsim 40 km/s.Comment: 5 pages, 2 figures. Poster contribution to the 13th Annual Astrophysics Conference in Maryland, The Emergence of Cosmic Structur

Rocket Plume Scaling for Orion Wind Tunnel Testing

A wind tunnel test program was undertaken to assess the jet interaction effects caused by the various solid rocket motors used on the Orion Launch Abort Vehicle (LAV). These interactions of the external flowfield and the various rocket plumes can cause localized aerodynamic disturbances yielding significant and highly non-linear control amplifications and attenuations. This paper discusses the scaling methodologies used to model the flight plumes in the wind tunnel using cold air as the simulant gas. Comparisons of predicted flight, predicted wind tunnel, and measured wind tunnel forces-and-moments and plume flowfields are made to assess the effectiveness of the selected scaling methodologies

Infrared Surface Brightness Fluctuations of the Coma Elliptical NGC 4874 and the Value of the Hubble Constant

We have used the Keck I Telescope to measure K-band surface brightness fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma cluster. We use deep HST WFPC2 optical imaging to account for the contamination due to faint globular clusters and improved analysis techniques to derive measurements of the SBF apparent magnitude. Using a new SBF calibration which accounts for the dependence of K-band SBFs on the integrated color of the stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10 Mpc) for the Coma cluster. The resulting value of the Hubble constant is 71+/-8 km/s/Mpc, not including any systematic error in the HST Cepheid distance scale.Comment: ApJ Letters, in press. Uses emulateapj5.st

Great Salt Lake Past and Present: Elevation and Salinity Changes to Utah\u27s Great Salt Lake from Railroad Causeway Alterations

In 1959, Union Pacific Railroad constructed a rock-filled causeway bisecting Utah’s Great Salt Lake, separating the lake into a north and south arm. Flow between the two arms was limited to two 4.6 meter wide culverts installed during original construction, an 88 meter breach opening installed in 1984, and the semi porous boulder and gravel causeway material. The south arm receives nearly all streamflows entering Great Salt Lake and a salinity gradient between the two arms developed over time. North arm salinity is often at or near saturation, averaging 317 g\L since 1966, while the south is considerably less saline, averaging 142 g\L since 1966. Ecological and industrial uses of the lake depend on salinity levels staying within physiologic and economic thresholds. Union Pacific Railroad proposed to replace aging culverts with a bridge, and provided four alternative bridge designs. Northern Utah’s variable climate complicates management of the causeway, where lake elevation and salinity are affected by wet and dry periods. Understanding the historical duration, magnitude, and frequency of wet and dry periods can inform future management decisions. I model the effect of each proposed bridge design on Great Salt Lake salinity and elevation in both arms by updating and applying US Geological Survey’s Great Salt Lake Fortran Model. I used measured historical streamflow and a 400-year tree-ring paleo-streamflow reconstruction to understand lake elevation and salinity sensitivity to longer-term climate variability. The model accurately simulates historical lake elevation and salinity and is sensitive to proposed bridge designs. Bridge alternatives vary salinity by 20 g\L within each arm using historical 1966-2012 conditions. When the model was run with the 400-year paleo-reconstructed hydrology, I find that the 20th century had the lowest average lake level of any century since 1600, and that 20th century floods were smaller than in previous centuries, both in terms of length and magnitude. With the 400-year paleo-streamflow model, differences of south arm salinity between bridge alternatives increase considerably through time, where alternative D results in salinity up to 100 g/l less than alternative A and that the current condition of the causeway would result in a fundamental change in Great Salt Lake characteristics, with the south arm approaching freshwater conditions at times. This research demonstrates that mass balance models are useful to predict management effects on terminal lake ecosystems, and provides a unique approach to reconstruct terminal lake paleo-salinity

Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4

We study dynamical properties of the anisotropic triangular quantum antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have established that the dynamical spin correlations cannot be understood within a linear spin wave analysis. We go beyond linear spin wave theory by taking interactions between magnons into account in a 1/S expansion. We determine the dynamical structure factor and carry out extensive comparisons with experimental data. We find that compared to linear spin wave theory a significant fraction of the scattering intensity is shifted to higher energies and strong scattering continua are present. However, the 1/S expansion fails to account for the experimentally observed large quantum renormalization of the exchange energies.Comment: 13 pages, 11 figures, higher quality figures can be obtained from the author