Industry workshop on large space structures: Executive summary

A NASA-sponsored Industry Workshop on Large Space Structures was convened at Langley Research Center on 24-26 February 1976. A number of structures specialists from seven major aerospace companies participated. Predictions about the future structures to be fabricated/assembled/erected in space are presented along with a composite appraisal of what the Aerospace Industry views as the critical structural technology developments needed to support NASA space missions in the 1985-2000 time frame

Notes on Certain (0,2) Correlation Functions

In this paper we shall describe some correlation function computations in perturbative heterotic strings that, for example, in certain circumstances can lend themselves to a heterotic generalization of quantum cohomology calculations. Ordinary quantum chiral rings reflect worldsheet instanton corrections to correlation functions involving products of Dolbeault cohomology groups on the target space. The heterotic generalization described here involves computing worldsheet instanton corrections to correlation functions defined by products of elements of sheaf cohomology groups. One must not only compactify moduli spaces of rational curves, but also extend a sheaf (determined by the gauge bundle) over the compactification, and linear sigma models provide natural mechanisms for doing both. Euler classes of obstruction bundles generalize to this language in an interesting way.Comment: 51 pages, LaTeX; v2: typos fixed; v3: more typos fixe

Communication perspectives on social networking and citizen journalism challenges to traditional newspapers

Communication perspectives are presented on the challenges posed to traditional newspapers by social media and citizen journalism, with special reference to the United States. This is an important topic given the critical role investigative reporting, long the domain of newspapers, plays in fostering democratic practices. New Media and social networking technology are evaluated in terms of their impact on the newspaper enterprise. Alternative scenarios for future developments are examined as are the implications for social values and the role of an informed citizenry in democratic society. Strategic management issues are analyzed, and the possibility is considered that social media can fulfill much of the democracy-enhancing role served traditionally by newspapers. --Newspapers,news industry,social media,social networks,democracy,journalism

The 't Hooft Model As A Hologram

We consider the 3d dual of 1+1 dimensional large-N_c QCD with quarks in the fundamental representation, also known as the 't Hooft model. 't Hooft solved this model by deriving a Schroedinger equation for the wavefunction of a parton inside the meson. In the scale-invariant limit, we show how this equation is related by a transform to the equation of motion for a scalar field in AdS_3. We thus find an explicit map between the `parton-x' variable and the radial coordinate of AdS_3. This direct map allows us to check the AdS/CFT prescription from the 2d side. We describe various features of the dual in the conformal limit and to the leading order in conformal symmetry breaking, and make some comments on the 3d theory in the fully non-conformal regime.Comment: Introduction expanded. References rearranged. The version published in JHE

Spectra of D-branes with Higgs vevs

In this paper we continue previous work on counting open string states between D-branes by considering open strings between D-branes with nonzero Higgs vevs, and in particular, nilpotent Higgs vevs, as arise, for example, when studying D-branes in orbifolds. Ordinarily Higgs vevs can be interpreted as moving the D-brane, but nilpotent Higgs vevs have zero eigenvalues, and so their interpretation is more interesting -- for example, they often correspond to nonreduced schemes, which furnishes an important link in understanding old results relating classical D-brane moduli spaces in orbifolds to Hilbert schemes, resolutions of quotient spaces, and the McKay correspondence. We give a sheaf-theoretic description of D-branes with Higgs vevs, including nilpotent Higgs vevs, and check that description by noting that Ext groups between the sheaves modelling the D-branes, do in fact correctly count open string states. In particular, our analysis expands the types of sheaves which admit on-shell physical interpretations, which is an important step for making derived categories useful for physics.Comment: 46 pages, LaTeX; v2: typos fixed; v3: more typos fixe

Heavy Thresholds, Slepton Masses and the μ\mu Term in Anomaly Mediated Supersymmetry Breaking

The effects of heavy mass thresholds on anomaly-mediated soft supersymmetry breaking terms are discussed. While heavy thresholds completely decouple to lowest order in the supersymmetry breaking, it is argued that they do affect the breaking terms at higher orders. The relevant contributions typically occur at lower order in the loop expansion compared to purely anomaly mediated contributions. The non decoupling contributions may be used to render models in which the only source of supersymmetry breaking is anomaly mediation viable, by generating positive contributions to the sleptons' masses squared. They can also be used to generate acceptable mu- and B-terms.Comment: 25 pages, late

D-branes, B fields, and Ext groups

In this paper we extend previous work on calculating massless boundary Ramond sector spectra of open strings to include cases with nonzero flat B fields. In such cases, D-branes are no longer well-modelled precisely by sheaves, but rather they are replaced by `twisted' sheaves, reflecting the fact that gauge transformations of the B field act as affine translations of the Chan-Paton factors. As in previous work, we find that the massless boundary Ramond sector states are counted by Ext groups -- this time, Ext groups of twisted sheaves. As before, the computation of BRST cohomology relies on physically realizing some spectral sequences. Subtleties that cropped up in previous work also appear here.Comment: 23 pages, LaTeX; v2: typos fixed; v3: reference adde

Entomopathogenic nematodes for biological control of codling moth

Entomopathogenic nematodes are often found naturally infecting codling moth larvae. The effect of an autumn treatment with S. feltiae on the fruit damage in the following summer was evaluated by treating 4 different apple orchards in October 2004 and 2005 at application rates of 3.75; 2 and 1.5 billion nematodes in 4000 l / ha. In three of the treated orchards, one treated with 3.75x109 nematodes/ha the other two treated with 2e9 nematode/ha, reduction in fruit damage was around 50%. In the most heavily infested orchard, which was treated with 1.5x109 nematode/ha only 33% reduction in fruit damage was achieved. Compared to previous studies, this was the first assessing the effect on the fruit damage in the summer following the treatment rather than assessing the mortality of sentinel larvae fixed to the treated tree trunks