Consistent Scenarios for Cosmic-Ray Excesses from Sommerfeld-Enhanced Dark Matter Annihilation

Anomalies in direct and indirect detection have motivated models of dark matter consisting of a multiplet of nearly-degenerate states, coupled by a new GeV-scale interaction. We perform a careful analysis of the thermal freezeout of dark matter annihilation in such a scenario. We compute the range of "boost factors" arising from Sommerfeld enhancement in the local halo for models which produce the correct relic density, and show the effect of including constraints on the saturated enhancement from the cosmic microwave background (CMB). We find that boost factors from Sommerfeld enhancement of up to ~800 are possible in the local halo. When the CMB bounds on the saturated enhancement are applied, the maximal boost factor is reduced to ~400 for 1-2 TeV dark matter and sub-GeV force carriers, but remains large enough to explain the observed Fermi and PAMELA electronic signals. We describe regions in the DM mass-boost factor plane where the cosmic ray data is well fit for a range of final states, and show that Sommerfeld enhancement alone is enough to provide the large annihilation cross sections required to fit the data, although for light mediator masses (less than ~200 MeV) there is tension with the CMB constraints in the absence of astrophysical boost factors from substructure. Additionally, we consider the circumstances under which WIMPonium formation is relevant and find for heavy WIMPs (greater than ~2 TeV) and soft-spectrum annihilation channels it can be an important consideration; we find regions with dark matter mass greater than 2.8 TeV that are consistent with the CMB bounds and have ~600-700 present-day boost factors.Comment: Related web application at http://astrometry.fas.harvard.edu/mvogelsb/sommerfeld . v2: added brief clarification regarding propagation parameters, plots now show effect of relaxing CMB bounds. 35 pages in JCAP format, 4 figures. Accepted for publication in JCA

Rate monotonic analysis for real-time systems

Rate monotonic analysis (RMA), a mathematical approach that helps ensure that a real-time system meets its performance requirements, is discussed. It does so through a collection of quantitative methods and algorithms that let engineers understand, analyze, and predict the timing behavior of their designs. An application of RMA to an air traffic control system is described. Document type: Repor

The Hamiltonian of the V15_{15} Spin System from first-principles Density-Functional Calculations

We report first-principles all-electron density-functional based studies of the electronic structure, magnetic ordering and anisotropy for the V$_{15}$ molecular magnet. From these calculations, we determine a Heisenberg Hamiltonian with four antiferromagnetic and one {\em ferromagnetic} coupling. We perform direct diagonalization to determine the temperature dependence of the susceptibility. This Hamiltonian reproduces the experimentally observed spin $S$=1/2 ground state and low-lying $S$=3/2 excited state. A small anisotropy term is necessary to account for the temperature independent part of the magnetization curve.Comment: 4 pages in RevTeX format + 2 ps-figures, accepted by PRL Feb. 2001 (previous version was an older version of the paper

A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle.

Biological carbon fixation is a key step in the global carbon cycle that regulates the atmosphere's composition while producing the food we eat and the fuels we burn. Approximately one-third of global carbon fixation occurs in an overlooked algal organelle called the pyrenoid. The pyrenoid contains the CO2-fixing enzyme Rubisco and enhances carbon fixation by supplying Rubisco with a high concentration of CO2 Since the discovery of the pyrenoid more that 130 y ago, the molecular structure and biogenesis of this ecologically fundamental organelle have remained enigmatic. Here we use the model green alga Chlamydomonas reinhardtii to discover that a low-complexity repeat protein, Essential Pyrenoid Component 1 (EPYC1), links Rubisco to form the pyrenoid. We find that EPYC1 is of comparable abundance to Rubisco and colocalizes with Rubisco throughout the pyrenoid. We show that EPYC1 is essential for normal pyrenoid size, number, morphology, Rubisco content, and efficient carbon fixation at low CO2 We explain the central role of EPYC1 in pyrenoid biogenesis by the finding that EPYC1 binds Rubisco to form the pyrenoid matrix. We propose two models in which EPYC1's four repeats could produce the observed lattice arrangement of Rubisco in the Chlamydomonas pyrenoid. Our results suggest a surprisingly simple molecular mechanism for how Rubisco can be packaged to form the pyrenoid matrix, potentially explaining how Rubisco packaging into a pyrenoid could have evolved across a broad range of photosynthetic eukaryotes through convergent evolution. In addition, our findings represent a key step toward engineering a pyrenoid into crops to enhance their carbon fixation efficiency

Improving Thermal Conduction Across Cathode/Electrolyte Interfaces in Solid-State Lithium-Ion Batteries by Hierarchical Hydrogen-Bond Network

Effective thermal management is an important issue to ensure safety and performance of lithium-ion batteries. Fast heat removal is highly desired but has been obstructed by the high thermal resistance across cathode/electrolyte interface. In this study, self-assembled monolayers (SAMs) are used as the vibrational mediator to tune interfacial thermal conductance between an electrode, lithium cobalt oxide (LCO), and a solid state electrolyte, polyethylene oxide (PEO). Embedded at the LCO/PEO interface, SAMs are specially designed to form hierarchical hydrogen-bond (H-bond) network with PEO. Molecular dynamics simulations demonstrate that all SAM-decorated interfaces show enhanced thermal conductance and dominated by H-bonds types. The incorporation of poly(acrylic acid) (PAA) SAM drastically enhances interfacial thermal conductance by approximately 211.69%, largely due to the formation of a strong H-bond, -COOH···:O, between PAA and PEO. Even with weaker H-bonds such as -OH···:O, it still outperforms the pristine interface as well as interfaces decorated with non-H-bonded SAMs, e.g. PE. Such improvement is attributed to the unique hierarchical H-bond network at the interface, which removes discontinuities in temperature field, straighten SAM chains, make materials strongly adhere, and couple the vibrational modes of materials. The study is expected to guide surface engineering for more effective thermal management in lithium-ion batteries

Rules for Growth: Promoting Innovation and Growth Through Legal Reform

The United States economy is struggling to recover from its worst economic downturn since the Great Depression. After several huge doses of conventional macroeconomic stimulus - deficit-spending and monetary stimulus - policymakers are understandably eager to find innovative no-cost ways of sustaining growth both in the short and long runs. In response to this challenge, the Kauffman Foundation convened a number of America’s leading legal scholars and social scientists during the summer of 2010 to present and discuss their ideas for changing legal rules and policies to promote innovation and accelerate U.S. economic growth. This meeting led to the publication of Rules for Growth: Promoting Innovation and Growth Through Legal Reform, a comprehensive and groundbreaking volume of essays prescribing a new set of growth-promoting policies for policymakers, legal scholars, economists, and business men and women. Some of the top Rules include: • Reforming U.S. immigration laws so that more high-skilled immigrants can launch businesses in the United States. • Improving university technology licensing practices so university-generated innovation is more quickly and efficiently commercialized. • Moving away from taxes on income that penalize risk-taking, innovation, and employment while shifting toward a more consumption-based tax system that encourages saving that funds investment. In addition, the research tax credit should be redesigned and made permanent. • Overhauling local zoning rules to facilitate the formation of innovative companies. • Urging judges to take a more expansive view of flexible business contracts that are increasingly used by innovative firms. • Urging antitrust enforcers and courts to define markets more in global terms to reflect contemporary realities, resist antitrust enforcement from countries with less sound antitrust regimes, and prohibit industry trade protection and subsidies. • Reforming the intellectual property system to allow for a post-grant opposition process and address the large patent application backlog by allowing applicants to pay for more rapid patent reviews. • Authorizing corporate entities to form digitally and use software as a means for setting out agreements and bylaws governing corporate activities. The collective essays in the book propose a new way of thinking about the legal system that should be of interest to policymakers and academic scholars alike. Moreover, the ideas presented here, if embodied in law, would augment a sustained increase in U.S. economic growth, improving living standards for U.S. residents and for many in the rest of the world

Digital methods for ethnography: analytical concepts for ethnographers exploring social media environments

The aim of this article is to introduce some analytical concepts suitable for ethnographers dealing with social media environments. As a result of the growth of social media, the Internet structure has become a very complex, fluid, and fragmented space. Within this space, it is not always possible to consider the 'classical' online community as the privileged field site for the ethnographer, in which s/he immerses him/herself. Differently, taking inspiration from some methodological principles of the Digital Methods paradigm, I suggest that the main task for the ethnographer moving across social media environments should not be exclusively that of identifying an online community to delve into but of mapping the practices through which Internet users and digital devices structure social formations around a focal object (e.g., a brand). In order to support the ethnographer in the mapping of social formations within social media environments, I propose five analytical concepts: community, public, crowd, self-presentation as a tool, and user as a device

Bird populations most exposed to climate change are less sensitive to climatic variation

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species' range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two co-familial European songbirds, the great tit (Parus major) and blue tit (Cyanistes caeruleus), covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity than those in evergreen and mixed habitats. However, populations with higher sensitivity tended to have experienced less rapid change in climate over the past decades, such that populations with high phenological sensitivity will not necessarily exhibit the strongest phenological advancement. Our results show that to effectively assess the impact of climate change on phenology across a species' range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population. Intra-specific variations may contribute to heterogeneous responses to climate change across a species' range. Here, the authors investigate the phenology of two bird species across their breeding ranges, and find that their sensitivity to temperature is uncoupled from exposure to climate change.Peer reviewe

DNA adducts of aristolochic acid II: total synthesis and site-specific mutagenesis studies in mammalian cells

Aristolochic acids I and II (AA-I, AA-II) are found in all Aristolochia species. Ingestion of these acids either in the form of herbal remedies or as contaminated wheat flour causes a dose-dependent chronic kidney failure characterized by renal tubulointerstitial fibrosis. In ∼50% of these cases, the condition is accompanied by an upper urinary tract malignancy. The disease is now termed aristolochic acid nephropathy (AAN). AA-I is largely responsible for the nephrotoxicity while both AA-I and AA-II are genotoxic. DNA adducts derived from AA-I and AA-II have been isolated from renal tissues of patients suffering from AAN. We describe the total synthesis, de novo, of the dA and dG adducts derived from AA-II, their incorporation site-specifically into DNA oligomers and the splicing of these modified oligomers into a plasmid construct followed by transfection into mouse embryonic fibroblasts. Analysis of the plasmid progeny revealed that both adducts blocked replication but were still partly processed by DNA polymerase(s). Although the majority of coding events involved insertion of correct nucleotides, substantial misincorporation of bases also was noted. The dA adduct is significantly more mutagenic than the dG adduct; both adducts give rise, almost exclusively, to misincorporation of dA, which leads to AL-II-dA→T and AL-II-dG→T transversions