Research in extreme ultraviolet and far ultraviolet astronomy

Instruments designed to explore different aspects of far and extreme ultraviolet cosmic radiation were studied. The far ultraviolet imager (FUVI) was flown on the Aries sounding rocket. Its unique large format 75mm detector mapped out the far ultraviolet background radiation with a resolution of only a few arc minutes. Analysis of this data indicates to what extent the FUVI background is extra galactic in origin. A power spectrum of the spatial fluctuations will have direct consequences for galactic evolution

Superconducting tunnel junction x-ray detectors for high resolution spectroscopy

We are developing low-tcmpaature detectors for optical, ultraviolet, X-ray, and gamma-ray spectroscopy, and for biomolecular mass spectrometry. We present here a some of our recent work in developing these detectors and some of the first results in applying these detectors to X-ray fluorescence analysis. We have measured thin-film Nb/Al/Al{sub 2}O{sub 3}/Al/Nb superconducting tunnel junction (STJ) X-ray detectors in the 0 2 to 1 keV band with a range of different junction sizes and aluminum film thicknesses. In one case, we have achieved the statistical limit to the energy resolution in this band. We have measured the performance of these STJ detectors as a function of count rate. and demonstrated a resolution of 13 eV FWHM at 271 eV with an output count rate of 20,600 cts/s Using X rays from SSRL to study compos- ite materials, we have demonstrated that we can resolve the L lines of transition metals from the nearby K lines of light elements We describe the first use of a low-temperature X-ray detector to measure X-ray fluoresccncc from the dilute metal component in a protein

Competition and Selection Among Conventions

In many domains, a latent competition among different conventions determines which one will come to dominate. One sees such effects in the success of community jargon, of competing frames in political rhetoric, or of terminology in technical contexts. These effects have become widespread in the online domain, where the data offers the potential to study competition among conventions at a fine-grained level. In analyzing the dynamics of conventions over time, however, even with detailed on-line data, one encounters two significant challenges. First, as conventions evolve, the underlying substance of their meaning tends to change as well; and such substantive changes confound investigations of social effects. Second, the selection of a convention takes place through the complex interactions of individuals within a community, and contention between the users of competing conventions plays a key role in the convention's evolution. Any analysis must take place in the presence of these two issues. In this work we study a setting in which we can cleanly track the competition among conventions. Our analysis is based on the spread of low-level authoring conventions in the eprint arXiv over 24 years: by tracking the spread of macros and other author-defined conventions, we are able to study conventions that vary even as the underlying meaning remains constant. We find that the interaction among co-authors over time plays a crucial role in the selection of them; the distinction between more and less experienced members of the community, and the distinction between conventions with visible versus invisible effects, are both central to the underlying processes. Through our analysis we make predictions at the population level about the ultimate success of different synonymous conventions over time--and at the individual level about the outcome of "fights" between people over convention choices.Comment: To appear in Proceedings of WWW 2017, data at https://github.com/CornellNLP/Macro

Modeling the power flow in normal conductor-insulator-superconductor junctions

Normal conductor-insulator-superconductor (NIS) junctions promise to be interesting for x-ray and phonon sensing applications, in particular due to the expected self-cooling of the N electrode by the tunneling current. Such cooling would enable the operation of the active element of the sensor below the cryostat temperature and at a correspondingly higher sensitivity. It would also allow the use of MS junctions as microcoolers. At present, this cooling has not been realized in large area junctions (suitable for a number of detector applications). In this article, we discuss a detailed modeling of the heat flow in such junctions; we show how the heat flow into the normal electrode by quasiparticle back-tunneling and phonon absorption from quasiparticle pair recombination can overcompensate the cooling power. This provides a microscopic explanation of the self-heating effects we observe in our large area NIS junctions. The model suggests a number of possible solutions

Voter Model with Time dependent Flip-rates

We introduce time variation in the flip-rates of the Voter Model. This type of generalisation is relevant to models of ageing in language change, allowing the representation of changes in speakers' learning rates over their lifetime and may be applied to any other similar model in which interaction rates at the microscopic level change with time. The mean time taken to reach consensus varies in a nontrivial way with the rate of change of the flip-rates, varying between bounds given by the mean consensus times for static homogeneous (the original Voter Model) and static heterogeneous flip-rates. By considering the mean time between interactions for each agent, we derive excellent estimates of the mean consensus times and exit probabilities for any time scale of flip-rate variation. The scaling of consensus times with population size on complex networks is correctly predicted, and is as would be expected for the ordinary voter model. Heterogeneity in the initial distribution of opinions has a strong effect, considerably reducing the mean time to consensus, while increasing the probability of survival of the opinion which initially occupies the most slowly changing agents. The mean times to reach consensus for different states are very different. An opinion originally held by the fastest changing agents has a smaller chance to succeed, and takes much longer to do so than an evenly distributed opinion.Comment: 16 pages, 6 figure

Utterance Selection Model of Language Change

We present a mathematical formulation of a theory of language change. The theory is evolutionary in nature and has close analogies with theories of population genetics. The mathematical structure we construct similarly has correspondences with the Fisher-Wright model of population genetics, but there are significant differences. The continuous time formulation of the model is expressed in terms of a Fokker-Planck equation. This equation is exactly soluble in the case of a single speaker and can be investigated analytically in the case of multiple speakers who communicate equally with all other speakers and give their utterances equal weight. Whilst the stationary properties of this system have much in common with the single-speaker case, time-dependent properties are richer. In the particular case where linguistic forms can become extinct, we find that the presence of many speakers causes a two-stage relaxation, the first being a common marginal distribution that persists for a long time as a consequence of ultimate extinction being due to rare fluctuations.Comment: 21 pages, 17 figure