The Changing Fractions of Type Ia Supernova NUV-Optical Subclasses with Redshift

UV and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have revealed the existence of two distinct color groups, NUV-red and NUV-blue events. The color curves differ primarily by an offset, with the NUV-blue u- color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-z SNe~Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We compare rest-frame UV/optical spectrophotometry of intermediate and high-z SNe Ia with UVOT photometry and HST spectrophotometry of low-z SNe Ia, finding that the same two color groups exist at higher-z, but with the NUV-blue events as the dominant group. Within each red/blue group, we do not detect any offset in color for different redshifts, providing insight into how SN~Ia UV emission evolves with redshift. Through spectral comparisons of SNe~Ia with similar peak widths and phase, we explore the wavelength range that produces the UV/OPT color differences. We show that the ejecta velocity of NUV-red SNe is larger than that of NUV-blue objects by roughly 12% on average. This velocity difference can explain some of the UV/optical color difference, but differences in the strengths of spectral features seen in meanspectra require additional explanation. Because of the different b-v colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to under-estimation of the optical luminosity of the NUV-blue SNe~Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.Comment: submitted to Ap

A Proof of Entropy Minimization for Outputs in Deletion Channels via Hidden Word Statistics

From the output produced by a memoryless deletion channel from a uniformly random input of known length $n$, one obtains a posterior distribution on the channel input. The difference between the Shannon entropy of this distribution and that of the uniform prior measures the amount of information about the channel input which is conveyed by the output of length $m$, and it is natural to ask for which outputs this is extremized. This question was posed in a previous work, where it was conjectured on the basis of experimental data that the entropy of the posterior is minimized and maximized by the constant strings $\texttt{000}\ldots$ and $\texttt{111}\ldots$ and the alternating strings $\texttt{0101}\ldots$ and $\texttt{1010}\ldots$ respectively. In the present work we confirm the minimization conjecture in the asymptotic limit using results from hidden word statistics. We show how the analytic-combinatorial methods of Flajolet, Szpankowski and Vall\'ee for dealing with the hidden pattern matching problem can be applied to resolve the case of fixed output length and $n\rightarrow\infty$, by obtaining estimates for the entropy in terms of the moments of the posterior distribution and establishing its minimization via a measure of autocorrelation.Comment: 11 pages, 2 figure

Optomechanical cooling in a continuous system

Radiation-pressure-induced optomechanical coupling permits exquisite control of micro- and mesoscopic mechanical oscillators. This ability to manipulate and even damp mechanical motion with light---a process known as dynamical backaction cooling---has become the basis for a range of novel phenomena within the burgeoning field of cavity optomechanics, spanning from dissipation engineering to quantum state preparation. As this field moves toward more complex systems and dynamics, there has been growing interest in the prospect of cooling traveling-wave phonons in continuous optomechanical waveguides. Here, we demonstrate optomechanical cooling in a continuous system for the first time. By leveraging the dispersive symmetry breaking produced by inter-modal Brillouin scattering, we achieve continuous mode optomechanical cooling in an extended 2.3-cm silicon waveguide, reducing the temperature of a band of traveling-wave phonons by more than 30 K from room temperature. This work reveals that optomechanical cooling is possible in macroscopic linear waveguide systems without an optical cavity or discrete acoustic modes. Moreover, through an intriguing type of wavevector-resolved phonon spectroscopy, we show that this system permits optomechanical control over continuously accessible groups of phonons and produces a new form of nonreciprocal reservoir engineering. Beyond this study, this work represents a first step towards a range of novel classical and quantum traveling-wave operations in continuous optomechanical systems.Comment: Manuscript with supplementary information. 17 pages, 4 Figures. Minor correction in Fig.

China Maritime Report No. 3: China’s Distant-Ocean Survey Activities: Implications for U.S. National Security

Today, the People’s Republic of China (PRC) is investing in marine scientific research on a massive scale. This investment supports an oceanographic research agenda that is increasingly global in scope. One key indicator of this trend is the expanding operations of China’s oceanographic research fleet. On any given day, 5-10 Chinese “scientific research vessels” (科学考查船) may be found operating beyond Chinese jurisdictional waters, in strategically-important areas of the Indo-Pacific. Overshadowed by the dramatic growth in China’s naval footprint, their presence largely goes unnoticed. Yet the activities of these ships and the scientists and engineers they embark have major implications for U.S. national security. This report explores some of these implications. It seeks to answer basic questions about the out-of-area—or “distant-ocean” (远洋)—operations of China’s oceanographic research fleet. Who is organizing and conducting these operations? Where are they taking place? What do they entail? What are the national drivers animating investment in these activities?https://digital-commons.usnwc.edu/cmsi-maritime-reports/1002/thumbnail.jp

Beyond the Wall: Chinese Far Seas Operation

This volume is the product of a groundbreaking dialogue on sea-lane security held between People\u27s Liberation Army (PLA) Navy and U.S. Navy scholars at the Naval War College in August 2013, with additional material from a related conference, China\u27s Far Seas Operations, hosted by the China Maritime Studies Institute in May 2012. At that time the political climate in China was uncertain, in the shadow of the Bo Xilai crisis and of the impending transition of power between the Hu and Xi regimes; accordingly the PLA Navy, though invited to participate in the Far Seas conference, ultimately declined to do so. This was not entirely surprising. Attempts by various agencies of the U.S. Navy up to that time to engage in discussions to advance maritime cooperation between China and the United States had been met with lukewarm responses at best. But at a maritime security dialogue in Dalian in September 2012 Senior Capt. Zhang Junshe of the PLA Navy Research Institute, a key contributor to this volume and to the success of the academic cooperation between our two institutes, approached Peter Dutton to tell him that everything had changed.https://digital-commons.usnwc.edu/cmsi-red-books/1012/thumbnail.jp

China\u27s Evolving Surface Fleet

The missile fast-attack craft and amphibious fleets of the People\u27s Liberation Army (PLA) Navy (PLAN) have undergone significant modernization over the past fifteen years. The capabilities of both categories of vessels have improved even if their actual numbers have not increased dramatically. Examined from the perspective of PLA doctrine and training, the missions of these forces represent the PLAN\u27s past, present, and future.https://digital-commons.usnwc.edu/cmsi-red-books/1013/thumbnail.jp

Leverage analysis: A method for locating points of influence in systemic design decisions

Many systemic design processes include the development and analysis of systems models that represent the issue(s) at hand. In causal loop diagram models, phenomena are graphed as nodes, with connections between them indicating a control relationship. Such models provide mechanisms for stakeholder collaboration, problem finding and generative insight and are powerful . These functions are valued in design thinking, but the potential of these models may yet be unfulfilled. We introduce the notion of “leverage measures” to systemic design, adapting techniques from social network analysis and systems dynamics to uncover key structures, relationships and latent leverage positions of modelled phenomena. We demonstrate their utility in a pilot study. By rethinking the logics of leverage, we make better arguments for change and find the place from which to move the world