Constraints on Extragalactic Point Source Flux from Diffuse Neutrino Limits

We constrain the maximum flux from extragalactic neutrino point sources by using diffuse neutrino flux limits. We show that the maximum flux from extragalactic point sources is E^2(dN/dE) < 1.4 x 10^-9 (L_nu/2x10^43 erg/s)^1/3 GeV cm-^2 s^-1 from individual point sources with average neutrino luminosity per decade, L_nu. It depends only slightly on factors such as the inhomogeneous matter density distribution in the local universe, the luminosity distribution, and the assumed spectral index. The derived constraints are at least one order of magnitude below the current experimental limits from direct searches. Significant constraints are also derived on the number density of neutrino sources and on the total neutrino power density.Comment: 7 pages, 3 figures, and 2 table

Cosmic-Ray Positrons: Are There Primary Sources?

Cosmic rays at the Earth include a secondary component originating in collisions of primary particles with the diffuse interstellar gas. The secondary cosmic rays are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.Comment: 15 pages, Latex, epsfig and aasms4 macros required, to appear in Astroparticle Physics (1999

Kikuchi ultrafast nanodiffraction in four-dimensional electron microscopy

Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size of the beam used, typically on the micron scale, the detection of nanoscale propagating waves in extended structures hitherto has not been reported. For elastic waves of complex motions, Bragg intensities contain all polarizations and they are not straightforward to disentangle. Here, we introduce Kikuchi diffraction dynamics, using convergent-beam geometry in an ultrafast electron microscope, to selectively probe propagating transverse elastic waves with nanoscale resolution. It is shown that Kikuchi band shifts, which are sensitive only to the tilting of atomic planes, reveal the resonance oscillations, unit cell angular amplitudes, and the polarization directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of Kikuchi's edges, and the magnitude of angular amplitude (0.3 mrad) and polarization [011] elucidate the nature of the motion: one that preserves the mass density (i.e., no compression or expansion) but leads to sliding of planes in the antisymmetric shear eigenmode of the elastic waveguide. As such, the method of Kikuchi diffraction dynamics, which is unique to electron imaging, can be used to characterize the atomic motions of propagating waves and their interactions with interfaces, defects, and grain boundaries at the nanoscale

The Costs of Free Entry: An Empirical Study of Real Estate Agents in Greater Boston

This paper studies the real estate brokerage industry in Greater Boston, an industry with low entry barriers and substantial turnover. Using a comprehensive dataset of agents and transactions from 1998-2007, we find that entry does not increase sales probabilities or reduce the time it takes for properties to sell, decreases the market share of experienced agents, and leads to a reduction in average service quality. These empirical patterns motivate an econometric model of the dynamic optimizing behavior of agents that serves as the foundation for simulating counterfactual market structures. A one-half reduction in the commission rate leads to a 73% increase in the number of houses each agent sells and benefits consumers by about $2 billion. House price appreciation in the first half of the 2000s accounts for 24% of overall entry and a 31% decline in the number of houses sold by each agent. Low cost programs that provide information about past agent performance have the potential to increase overall productivity and generate significant social savings.

An Update on the Phenotype, Genotype and Neurobiology of ADCY5-Related Disease.

Adenylyl cyclase 5 (ADCY5)-related phenotypes comprise an expanding disease continuum, but much remains to be understood about the underlying pathogenic mechanisms of the disease. ADCY5-related disease comprises a spectrum of hyperkinetic disorders involving chorea, myoclonus, and/or dystonia, often with paroxysmal exacerbations. Hypotonia, developmental delay, and intellectual disability may be present. The causative gene encodes adenylyl cyclase, the enzyme responsible for the conversion of adenosine triphosphate (ATP) to cyclic adenosine-3',5'-monophosphate (cAMP). cAMP is a second messenger that exerts a wide variety of effects via several intracellular signaling pathways. ADCY5 is the most commonly expressed isoform of adenylyl cyclase in medium spiny neurons (MSNs) of the striatum, and it integrates and controls dopaminergic signaling. Through cAMP pathway, ADCY5 is a key regulator of the cortical and thalamic signaling that control initiation of voluntary movements and prevention of involuntary movements. Gain-of-function mutations in ADCY5 have been recently linked to a rare genetic disorder called ADCY5-related dyskinesia, where dysregulation of the cAMP pathway leads to reduced inhibitory activity and involuntary hyperkinetic movements. Here, we present an update on the neurobiology of ADCY5, together with a detailed overview of the reported clinical phenotypes and genotypes. Although a range of therapeutic approaches has been trialed, there are currently no disease-modifying treatments. Improved in vitro and in vivo laboratory models will no doubt increase our understanding of the pathogenesis of this rare genetic movement disorder, which will improve diagnosis, and also facilitate the development of precision medicine approaches for this, and other forms of hyperkinesia

Illuminating dark matter and primordial black holes with interstellar antiprotons

Interstellar antiproton fluxes can arise from dark matter annihilating or decaying into quarks or gluons that subsequently fragment into antiprotons. Evaporation of primordial black holes also can produce a significant antiproton cosmic-ray flux. Since the background of secondary antiprotons from spallation has an interstellar energy spectrum that peaks at \sim 2\gev and falls rapidly for energies below this, low-energy measurements of cosmic antiprotons are useful in the search for exotic antiproton sources. However, measurement of the flux near the earth is challenged by significant uncertainties from the effects of the solar wind. We suggest evading this problem and more effectively probing dark-matter signals by placing an antiproton spectrometer aboard an interstellar probe currently under discussion. We address the experimental challenges of a light, low-power-consuming detector, and present an initial design of such an instrument. This experimental effort could significantly increase our ability to detect, and have confidence in, a signal of exotic, nonstandard antiproton sources. Furthermore, solar modulation effects in the heliosphere would be better quantified and understood by comparing results to inverse modulated data derived from existing balloon and space-based detectors near the earth.Comment: 18 pages, 3 figure

4D visualization of embryonic, structural crystallization by single-pulse microscopy

In many physical and biological systems the transition from an amorphous to ordered native structure involves complex energy landscapes, and understanding such transformations requires not only their thermodynamics but also the structural dynamics during the process. Here, we extend our 4D visualization method with electron imaging to include the study of irreversible processes with a single pulse in the same ultrafast electron microscope (UEM) as used before in the single-electron mode for the study of reversible processes. With this augmentation, we report on the transformation of amorphous to crystalline structure with silicon as an example. A single heating pulse was used to initiate crystallization from the amorphous phase while a single packet of electrons imaged selectively in space the transformation as the structure continuously changes with time. From the evolution of crystallinity in real time and the changes in morphology, for nanosecond and femtosecond pulse heating, we describe two types of processes, one that occurs at early time and involves a nondiffusive motion and another that takes place on a longer time scale. Similar mechanisms of two distinct time scales may perhaps be important in biomolecular folding

Playing games with cultural heritage: a comparative case study analysis of the current status of digital game preservation

Digital games are major part of popular culture. They are also an important part of the history of play and as such they deserve to take their rightful place in our cultural legacy. However, they have received little attention in the academic literature on preservation. Despite this lack of interest, some institutions have recognized the significance of preventing the loss of these valuable materials but to what extent is their longevity ensured? What is the current status of game preservation? What are the challenges facing institutions as they ‘‘play games with cultural heritage?’’ This article provides an overview of the current state of play and, using a comparative case study analysis, provides an insight into the issues, which lie ahead

Where have all the games gone? Explorations on the cultural significance of digital games and preservation

It is now 50 years since the development of the first computer game but despite the proliferation of digital games in our society - with an industry which is flourishing and an average of 9 games sold every second of every day in 2007, it seems that these products are not as valued as the products of other cultural industries, such as film and television, and they are being excluded from the preservation of our digital heritage. This paper will focus on research interviews undertaken with people in the academic community. It will highlight that the growing academic interest in digital games is being hindered by a lack of research collections to support historical study. Researchers acknowledge that the study of digital games is a relatively new discipline and that outside academia, there is still little understanding of their cultural significance. However, they recognise the importance of protecting games as part of our digital heritage to ensure that future generations are able to understand the development of a valuable aspect of our social history. In other words, this research has underlined that games are considered a culture worth studying and something in need of preserving

The barriers to the preservation of digital games: questions on cultural significance

Digital games have become an increasingly visible and popular leisure activity in the 21st century. Despite this proliferation in our society, it seems that they are not valued as part of our culture in the same way as products such as film and music. Furthermore, digital games are a largely ignored part of our cultural heritage. Dismissed as “at best recreational, and at worst desensitizing and degenerate” (Neiburger, 2007, p. 28), they have not specifically been addressed in most of the academic literature on digital preservation and represent a serious omission in past research. This essay discusses this gap in the research in relation to evidence of the cultural significance of digital games, the potential barriers to their acceptance as part of our cultural heritage, and how this relates to the preservation of digital games as cultural artifacts. First, the current status of digital games in our society and the size and strength of the digital games industry is considered. Second, the current interest from academia in digital games is explored. Third, the current preservation activities and the limitations of these initiatives are reviewed. Finally, the barriers to the preservation of digital games in relation to their status as a new cultural phenomenon, their relationship to traditional institutions, and perceptions of their value in terms of selection policies for preservation are examined