Repetitive Delone Sets and Quasicrystals

This paper considers the problem of characterizing the simplest discrete point sets that are aperiodic, using invariants based on topological dynamics. A Delone set whose patch-counting function N(T), for radius T, is finite for all T is called repetitive if there is a function M(T) such that every ball of radius M(T)+T contains a copy of each kind of patch of radius T that occurs in the set. This is equivalent to the minimality of an associated topological dynamical system with R^n-action. There is a lower bound for M(T) in terms of N(T), namely N(T) = O(M(T)^n), but no general upper bound. The complexity of a repetitive Delone set can be measured by the growth rate of its repetitivity function M(T). For example, M(T) is bounded if and only if the set is a crystal. A set is called is linearly repetitive if M(T) = O(T) and densely repetitive if M(T) = O(N(T))^{1/n}). We show that linearly repetitive sets and densely repetitive sets have strict uniform patch frequencies, i.e. the associated topological dynamical system is strictly ergodic. It follows that such sets are diffractive. In the reverse direction, we construct a repetitive Delone set in R^n which has M(T) = O(T(log T)^{2/n}(log log log T)^{4/n}), but does not have uniform patch frequencies. Aperiodic linearly repetitive sets have many claims to be the simplest class of aperiodic sets, and we propose considering them as a notion of "perfectly ordered quasicrystal".Comment: To appear in "Ergodic Theory and Dynamical Systems" vol.23 (2003). 37 pages. Uses packages latexsym, ifthen, cite and files amssym.def, amssym.te

Quantitative Spectroscopy of Supernovae for Dark Energy Studies

Detailed quantitative spectroscopy of Type Ia supernovae (SNe~Ia) provides crucial information needed to minimize systematic effects in both ongoing SNe Ia observational programs such as the Nearby Supernova Factory, ESSENCE, and the SuperNova Legacy Survey (SNLS) and in proposed JDEM missions such as SNAP, JEDI, and DESTINY. Quantitative spectroscopy is mandatory to quantify and understand the observational strategy of comparing ``like versus like''. It allows us to explore evolutionary effects, from variations in progenitor metallicity to variations in progenitor age, to variations in dust with cosmological epoch. It also allows us to interpret and quantify the effects of asphericity, as well as different amounts of mixing in the thermonuclear explosion.Comment: White paper submitted to the Dark Energy Task Force, 13 pages, 5 figure

Classificatory struggles in the midst of austerity: policing or politics?

This article reports findings on class identities amongst a small sample of mainly working-class residents in the City of Salford. We attempt to develop a Rancièrian framework for understanding class identities, centred on his key concept of dissensus, and how these ideas have been developed by Imogen Tyler through the notion of ‘classificatory struggles’. From this, we identify a continuum of responses that are discernible in relation to the neoliberal order of classifications: from those orientated to a ‘policing’ function, either accepting and internalising dominant discourses or attempting to displace abjection onto others, to those that tend more towards ‘politics’ in either asserting alternative circuits of value or through an appeal to the name of the proletariat as a political claim to radical equality. In examining our data, we note that although a majority disavowed an explicit working-class identity, they nonetheless engaged in a range of classificatory struggles

Bridge Damage Models for Seismic Risk Assessment of Oregon Highway Network

The highway transportation network of the United States relies on the health and integrity of major infrastructure elements such as bridges. Frequently traveled parts of Oregon are within the seismically active Pacific Northwest and many of the bridges were designed and built to lateral demands that were assumed to be less than the current expectation, a deficiency caused by our growing awareness of seismic hazard and our enhanced understanding of the non-linear response of bridges. This vulnerability to damage from earthquakes can result in not only immediate damage, but also in potentially lingering economic impact caused by the disruption to traffic and freight mobility. Using analytical methods, fragility curves were constructed assuming lognormal capacity and demand distributions. Probability of failure was determined for the four damage state conditions of slight, moderate, extensive, and complete levels of damage. These statistical values were compared to the median and dispersion values proposed by other researchers, in addition to those calculated using guidelines from the HAZUS Technical Manual. Older multiple-span Oregon bridges were found to be significantly more fragile than the HAZUS models. As a result of this modeling and analysis effort, the relative fragility of the modeled typical 3-span and 5-span bridges was determined and quantified. Possible causes of the relatively high fragilities were also considered

Oral and Written Transmission in Ethiopian Christian Chant

Of all the musical traditions in the world among which fruitful comparisons with medieval European chant might be made, the chant tradition of the Ethiopian Orthodox Church promises to be especially informative. In Ethiopia one can actually witness many of the same processes of oral and written transmission as were or may have been active in medieval Europe. Music and literacy are taught in a single curriculum in ecclesiastical schools. Future singers begin to acquire the repertory by memorising chants that serve both as models for whole melodies and as the sources of the melodic phrases linked to individual notational signs. At a later stage of training each one copies out a complete notated manuscript on parchment using medieval scribal techniques. But these manuscripts are used primarily for study purposes; during liturgical celebrations the chants are performed from memory without books, as seems originally to have been the case also with Gregorian and Byzantine chant. Finally, singers learn to improvise sung liturgical poetry according to a structured system of rules. If one desired to imitate the example of Parry and Lord, who investigated the modern South Slavic epic for possible clues to Homeric poetry, it would be difficult to find a modern culture more similar to the one that spawned Gregorian chant.African and African American StudiesMusi

Evaluating the Use of Ocean Models of Different Complexity in Climate Change Studies

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).The study of the uncertainties in future climate projections requires large ensembles of simulations with different values of model characteristics that define its response to external forcing. These characteristic include climate sensitivity, strength of aerosol forcing and the rate of ocean heat uptake. The latter can be easily varied over a wide range in an anomaly diffusing ocean model (ADOM). The rate of heat uptake in a three-dimensional ocean general circulation model (OGCM) is, however, defined by large number of factors and is far more difficult to vary. Necessity to obtain a realistic ocean circulation places additional constraints, making it impossible to cover the range of values suggested by observations. As a result, a simpler model like an ADOM needs to be used in uncertainty studies. To evaluate the performance of the ADOM on different time scales we compare results of simulations with two versions of the MIT Integrated Global System Model (IGSM): one with a ADOM and the second with a full three-dimensional OCGM. Our results show that through the 20th and 21st century, the version of the IGSM with ADOM is able to reproduce important aspects of the climate response simulated by the version with the OCGM. However, the inability of the ADOM to depict feedbacks associated with the changes in the ocean circulation significantly affects its performance on the longer timescales. In particular, the ADOM overestimates sea level rise due to thermal expansion of the deep ocean. It also rather poorly depicts long term changes in oceanic carbon uptake, leading to underestimation of the atmospheric CO2 concentrations. Thus, the IGSM version with ADOM can be used to obtain probability distributions of changes in many of the important climate variables through the end of 21st century. On the other hand, studying longer-term climate change requires the use of the OGCM.This research was supported by the U.S Department of Energy, U.S. Environmental Protection Agency, U.S. National Science Foundation, U.S. National Aeronautics and Space Administration, U.S. National Oceanographic and Atmospheric Administration; and the Industry and Foundation Sponsors of the MIT Joint Program on the Science and Policy of Global Change: Alstom Power (France), American Electric Power (USA), Chevron Corporation (USA), CONCAWE (Belgium), DaimlerChrysler AG (Germany), Duke Energy (USA), J-Power (Japan), Electric Power Research Institute (USA), Electricité de France, ExxonMobil Corporation (USA), Ford Motor Company (USA), General Motors (USA), Murphy Oil Corporation (USA), Oglethorpe Power Corporation (USA), RWE Power (Germany), Schlumberger (USA), Shell Petroleum (Netherlands/UK), Southern Company (USA), Statoil ASA (Norway), Tennessee Valley Authority (USA), Tokyo Electric Power Company (Japan), Total (France), G. Unger Vetlesen Foundation (USA)

A Three-Dimensional Ocean-Seaice-Carbon Cycle Model and its Coupling to a Two-Dimensional Atmospheric Model: Uses in Climate Change Studies

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).We describe the coupling of a three-dimensional ocean circulation model, with explicit thermodynamic seaice and ocean carbon cycle representations, to a two-dimensional atmospheric/land model. This coupled system has been developed as an efficient and flexible tool with which to investigate future climate change scenarios. The setup is sufficiently fast for large ensemble simulations that address uncertainties in future climate modeling. However, the ocean component is detailed enough to provide a tool for looking at the mechanisms and feedbacks that are essential for understanding the future changes in the ocean system. Here we show results from a single example simulation: a spin-up to pre-industrial steady state, changes to ocean physical and biogeochemical states for the 20th century (where changes in greenhouse gases and aerosol concentrations are taken from observations) and predictions of further changes for the 21st century in response to increased greenhouse gas and aerosol emissions. We plan, in future studies to use this model to investigate processes important to the heat uptake of the oceans, changes to the ocean circulation and mechanisms of carbon uptake and how these will change in future climate scenarios

Relative Roles of Climate Sensitivity and Forcing in Defining the Ocean Circulation Response to Climate Change

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).The response of the ocean’s meridional overturning circulation (MOC) to increased greenhouse gas forcing is examined using a coupled model of intermediate complexity, including a dynamic 3D ocean subcomponent. Parameters are the increase in CO2 forcing (with stabilization after a specified time interval) and the model’s climate sensitivity. In this model, the cessation of deep sinking in the north “Atlantic” (hereinafter, a “collapse”), as indicated by changes in the MOC, behaves like a simple bifurcation. The final surface air temperature (SAT) change, which is closely predicted by the product of the radiative forcing and the climate sensitivity, determines whether a collapse occurs. The initial transient response in SAT is largely a function of the forcing increase, with higher sensitivity runs exhibiting delayed behavior; accordingly, high CO2-low sensitivity scenarios can be assessed as a recovering or collapsing circulation shortly after stabilization, whereas low CO2-high sensitivity scenarios require several hundred additional years to make such a determination. We also systemically examine how the rate of forcing, for a given CO2 stabilization, affects the ocean response. In contrast with previous studies based on results using simpler ocean models, we find that except for a narrow range of marginally stable to marginally unstable scenarios, the forcing rate has little impact on whether the run collapses or recovers. In this narrow range, however, forcing increases on a time scale of slow ocean advective processes results in weaker declines in overturning strength and can permit a run to recover that would otherwise collapse.This research was supported in part by the Methods and Models for Integrated Assessments Program of the National Science Foundation, Grant ATM-9909139, by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-93ER61677, and by the MIT Joint Program on the Science and Policy of Global Change (JPSPGC)

Inhibition of vascular endothelial growth factor with a sequence-specific hypoxia response element antagonist

Vascular endothelial growth factor (VEGF) and its receptors have been implicated as key factors in tumor angiogenesis that are up-regulated by hypoxia. We evaluated the effects of DNA-binding small molecules on hypoxia-inducible transcription of VEGF. A synthetic pyrrole-imidazole polyamide designed to bind the hypoxia response element (HRE) was found to disrupt hypoxia-inducible factor (HIF) binding to HIRE. In cultured HeLa cells, this resulted in a reduction of VEGF mRNA and secreted protein levels. The observed effects were polyamide-specific and dose-dependent. Analysis of genome-wide effects of the HIRE-specific polyamide revealed that a number of hypoxia-inducible genes were down-regulated. Pathway-based regulation of hypoxia-inducible gene expression with DNA-binding small molecules may represent a new approach for targeting angiogenesis