Contributions to the life history of juvenile blueback herring (Alosa aestivalis): Phototactic behavior and population dynamics

This research investigated the relationship between juvenile abundance indexes (JAIs) for anadromous blueback herring (Alosa aestivalis) and abiotic factors (river flow and temperature) during the spawning and nursery period in the tidal freshwater areas of James, Pamunkey, Mattaponi, and Rappahannock Rivers in Virginia. Accomplishing this objective required the evaluation of the JAI methodology, specifically the effect of phototactic behavior on diel changes in the surface availability to the pushnet sampling gear, and obtaining population dynamics information (hatch dates, growth, natural mortality) during early life history from otolith microstructure of samples collected in 1991 and 1992. Mean catch-per-unit effort (CPUE) at night was one to two orders-of-magnitude higher than daytime mean CPUE. Availability dramatically increased approximately 30 minutes after sunset when light intensity was 10&\sp{lcub}-2{rcub}& to 10&\sp{lcub}-3{rcub}& &u&E/m&\sp2&/s. After the occurrence of this isolume, consecutive catches were order independent and varied without trend. A corresponding change in availability of prey did not occur, indicating that juveniles migrate to surface water in a specific isolume and not as a response to prey movement. Phototropic research verified the appropriateness of the JAI sampling methodology. Otolith microstructure analysis indicated that later larval emergence, reduced relative abundance, depressed growth, and increased mortality were associated with low water temperature and high river flow from a major episodic event. Results suggest that high river flows during the early larval period increase turbidity and reduce prey visibility, potentially causing depressed growth and starvation of newly hatched larvae. No linear or nonlinear relationship, however, was evident between any of the seasonal and monthly abiotic factors and the annual JAIs for the period 1979-95. All correlation and multiple regression analyses failed to reject (P &\u3e& 0.05) the hypothesis of no effect. While the statistical power to detect a strong effect was high (&\u3e&0.80), the power to detect weak effects was low, perhaps because of limited sample size and the lack of major runoff events during the study period. Power analyses indicated that the detection of a weak effect with the observed variance would require 25 or more years of data

A Stock Assessment Program for Chesapeake Bay Fisheries: Development of an Alosa Juvenile Index of Abundance: Annual Report 1991

This presentation is the annual report for Contract No. NA17FUO196-0l A Stock Assessment Program for Chesapeake Bay Fisheries: Development of an Alosa Juvenile Index of Abundance, for the period 1 May 1991 to 31 May 1992. The fishes of concern were the alewife (Alosa pseudoharengus), American shad (& sapidissima), and the blueback herring (A. aestivalis)

A Stock Assessment Program for Chesapeake Bay Fisheries: Development of an Alosa Juvenile Index of Abundance: Annual Report 1990

This presentation is the annual report for Contract No. NA90AA-H-SF671 A Stock Assessment Program for Chesapeake Bay Fisheries: Development of an Alosa Juvenile Index of Abundance, for the period 15 June 1990 to 31 July 1991. The fishes of concern were the alewife (Alosa pseudoharengus), American shad (A. sapidissima), and the blueback herring (A. aestivalis). The abundance of the Alosa stocks, once an important component of the landings of Virginia fisheries, have dramatically decreased in the last decade. The 1981 landings of Alosa species in Virginia were the lowest ever recorded. American shad and river herring are also pursued by recreational fisherman in Virginia, however, the extent and success of this activity is largely unknown. Additionally, these species have a vital ecological role. Young-of-the-year Alosa are the dominant pelagic prey species in their extensive freshwater and upper estuarine nursery grounds. After spawning, adults return to the sea and are prey of many marine piscivores. It is important that studies of the Alosa stocks in Virginia be continued. Current data, as well as historical data, are needed in order that data analyses may make constructive contributions to rational management strategies

Closed string radiation from moving D-branes

We compute the amplitude for the radiation of massless NS-NS closed string states from the interaction of two moving D-branes. We consider particle-like D-branes with reference to 4-dimensional spacetime, in toroidal and orbifold compactifications, and we work out the relevant world sheet propagators within the moving boundary state formalism. We find no on-shell axion emission. For large inter-brane separation, we compute the spacetime graviton emission amplitude and estimate the average energy radiated, whereas the spacetime dilaton amplitude is found to vanish in this limit. The possibility of emission of other massless states depends on the nature of the branes and of the compactification scheme.Comment: 41 pages, LaTe

An Orbifold of Type 0B Strings and Non-supersymmetric Gauge Theories

We study a {{\IZ}}_2 orbifold of Type 0B string theory by reflection of six of the coordinates (this theory may also be thought of as a {{\IZ}}_4 orbifold of Type IIB string theory by a rotation by $\pi$ in three independent planes). We show that the only massless mode localized on the fixed fourplane \IR^{3,1} is a U(1) gauge field. After introducing D3-branes parallel to the fixed fourplane we find non-supersymmetric non-abelian gauge theories on their worldvolume. One of our results is that the theory on equal numbers of electric and magnetic D3-branes placed at the fourplane is the {{\IZ}}_4 orbifold of ${\cal N}=4$ supersymmetric Yang-Mills theory by the center of its R-symmetry group.Comment: 15 pages, harvmac; v2: very minor corrections; v3: a comment about pure glue theory adde

Anti-de-Sitter Island-Universes from 5D Standing Waves

We construct simple standing wave solutions in a 5D space-time with a ghost scalar field. The nodes of these standing waves are 'islands' of 4D Minkowski space-time. For the 5D model with increasing (decreasing) warp factor there are a finite (infinite) number of nodes and thus Minkowski island-universes having different parameters, such as gravitational and cosmological constants. This feature is similar to the assumptions of the landscape models, which postulate a large number of universes with different parameters. This standing wave solution also provides a new localization mechanism - matter fields can reside only on Minkowski 'islands', where the background space-time does not oscillate.Comment: 14 page pre-print format. Discussion about connection to Weyl gravity added and "E&M" localization method added. To be published MPL

Product CFTs, gravitational cloning, massive gravitons and the space of gravitational duals

The question of graviton cloning in the context of the bulk/boundary correspondence is considered. It is shown that multi-graviton theories can be obtained from products of large-N CFTs. No more than one interacting massless graviton is possible. There can be however, many interacting massive gravitons. This is achieved by coupling CFTs via multi-trace marginal or relevant perturbations. The geometrical structure of the gravitational duals of such theories is that of product manifolds with their boundaries identified. The calculational formalism is described and the interpretation of such theories is discussed.Comment: Latex, 25 pages. (v2) Minor corrections and references adde

Building a Better Racetrack

We find IIb compactifications on Calabi-Yau orientifolds in which all Kahler moduli are stabilized, along lines suggested by Kachru, Kallosh, Linde and Trivedi.Comment: 47 pages, 1 figure, harvmac (v2: added references, minor comments, v3: improved discussion of metastability and explicit flux vacua

Limits of minimal models and continuous orbifolds

The lambda=0 't Hooft limit of the 2d W_N minimal models is shown to be equivalent to the singlet sector of a free boson theory, thus paralleling exactly the structure of the free theory in the Klebanov-Polyakov proposal. In 2d, the singlet sector does not describe a consistent theory by itself since the corresponding partition function is not modular invariant. However, it can be interpreted as the untwisted sector of a continuous orbifold, and this point of view suggests that it can be made consistent by adding in the appropriate twisted sectors. We show that these twisted sectors account for the `light states' that were not included in the original 't Hooft limit. We also show that, for the Virasoro minimal models (N=2), the twisted sector of our orbifold agrees precisely with the limit theory of Runkel & Watts. In particular, this implies that our construction satisfies crossing symmetry.Comment: 33 pages; v2: minor improvements and references added, published versio