Asymptotic ensemble stabilizability of the Bloch equation

In this paper we are concerned with the stabilizability to an equilibrium point of an ensemble of non interacting half-spins. We assume that the spins are immersed in a static magnetic field, with dispersion in the Larmor frequency, and are controlled by a time varying transverse field. Our goal is to steer the whole ensemble to the uniform "down" position. Two cases are addressed: for a finite ensemble of spins, we provide a control function (in feedback form) that asymptotically stabilizes the ensemble in the "down" position, generically with respect to the initial condition. For an ensemble containing a countable number of spins, we construct a sequence of control functions such that the sequence of the corresponding solutions pointwise converges, asymptotically in time, to the target state, generically with respect to the initial conditions. The control functions proposed are uniformly bounded and continuous

An investigation of the use of otolith microchemistry to discriminate reef fish populations and assess the movement of individuals.

The main objective of this thesis was to assess the degree of connectivity among populations of two highly abundant Caribbean reef fish (Stegasies partitus, Bicolor damselfish, and Haemulon flovolineatum , French grunt) at specific, but different portions of their life history; pelagic and demersal stages. In Chapter 2 (Section A) I assessed the classification of individuals to the site and time they were collected. The classification of S. partitus to their collection sites, separated by as little as 5 km, was moderately successful, while investigations of the temporal variability revealed substantial variability at the scale of two weeks. This spatial and temporal variability in otolith microchemistry suggested that investigations of connectivity were possible, but would require frequent recalibration of chemical signatures. Because the connectivity analysis of Chapter 2 relied upon the spatial variability in otolith chemistry, I investigated how the discrimination of populations could be improved in Chapter 3. An assumption of the connectivity analysis used in Chapter 2 was that otolith elemental concentrations did not differ between fish of different life stages (i.e., larval/pelagic stage with its core chemistry versus juvenile/demersal stage with its edge chemistry). In Chapter 4, I assessed whether there was ontogenetic variability in otolith microchemistry by comparing the otolith chemistry of pre-hatch embryos to that of post-settlement juveniles collected at the same site and time. Results indicated that elemental concentrations of embryo otoliths were between 2 and 325 times greater than that of juvenile edge chemistry (and 2 to 94 times greater than water chemistry) for Mn, Zn, Ba, Ce, and Pb. In Chapter 5 of Section B, I focused on the demersal stage of reef fish and whether otolith microchemistry could be used to discriminate H. flavolineatum caged in adjacent mangrove and coral reef sites in Belize and Bahamas. Significant variability in otolith trace elemental chemistry was detected among sites and habitats, which resulted in the classification of individuals separated by as little as 0.25 km (average correct classifications was between 68% and 85%). In Chapter 6, I expanded the sampling of H. favolineatum (19 sites throughout Turneffe Atoll: 9 mangrove and 11 reef sites, separated by 0.8 to 20m kms) to assess the extent to which individuals could be correctly assigned to the sites from which they were collected when natural movements were permitted (i.e., in the absence of cages, see Chapter 5). In Chapter 7, I discuss the findings of each of these chapters in the context of using otolith microchemistry in ecological investigations. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2005 .C45. Source: Dissertation Abstracts International, Volume: 66-11, Section: B, page: 5776. Thesis (Ph.D.)--University of Windsor (Canada), 2005

The effects of spatial scale on the structure of coral reef fish populations and assemblages.

A fundamental question in ecology is how spatial scale can influence the distribution and abundance of species and the structure of assemblages. The purpose of this work was to: (A) examine coral reef fish assemblages of St. Croix, U.S. Virgin Islands for species-area relationships; (B) understand what determines this relationship; and (C) determine relationships between habitat variables and assemblages and populations of reef fish at several spatial scales. Results indicated a positive relationship between species richness of reef fish and coral reef area at all reef sites (n = 14), where log10 area explained 66--96% of the variation in log 10 species richness. Tests were then conducted to understand what determined the species-area relationships. Five independent tests indicated that the random placement hypothesis did not entirely account for the species-area relationship. Instead habitat diversity and habitat influence hypotheses were found to better explain the variation in species richness. Upon closer examination of relationships between habitat variables and populations and assemblages of reef fish, it was determined that habitat variables that significantly accounted for variation in abundances of individuals and/or species richness varied across spatial scales as well as biological levels of resolution.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2000 .C45. Source: Masters Abstracts International, Volume: 39-02, page: 0442. Adviser: P. F. Sale. Thesis (M.Sc.)--University of Windsor (Canada), 2000

Recent Region-wide Declines in Caribbean Reef Fish Abundance

Profound ecological changes are occurring on coral reefs throughout the tropics, with marked coral cover losses and concomitant algal increases, particularly in the Caribbean region. Historical declines in the abundance of large Caribbean reef fishes likely reflect centuries of overexploitation. However, effects of drastic recent degradation of reef habitats on reef fish assemblages have yet to be established. By using meta-analysis, we analyzed time series of reef fish density obtained from 48 studies that include 318 reefs across the Caribbean and span the time period 1955–2007. Our analyses show that overall reef fish density has been declining significantly for more than a decade, at rates that are consistent across all subregions of the Caribbean basin (2.7% to 6.0% loss per year) and in three of six trophic groups. Changes in fish density over the past half-century are modest relative to concurrent changes in benthic cover on Caribbean reefs. However, the recent significant decline in overall fish abundance and its consistency across several trophic groups and among both fished and nonfished species indicate that Caribbean fishes have begun to respond negatively to habitat degradation

Habitat Associations of Juvenile Fish at Ningaloo Reef, Western Australia: The Importance of Coral and Algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority

Investigating the contribution of kelp- and eelgrass-derived carbon and nitrogen to marine herbivores and carnivores in Puget Sound.

In the Salish Sea Nereocystis luetkeana (bull kelp) and Zostera marina (eelgrass) are highly productive and because of their three-dimensional size and structure are reported to provide shelter for a variety of valued Puget Sound species, including Species of Concern like Chinook salmon, Oncorhynchus tshawytscha, and quillback rockfish, Sebastes maliger. Less understood is the extent to which bull kelp forests and eelgrass beds are a source of energy for invertebrates and fishes. To answer this question we conducted a project in 2018 and 2019 to reconstruct the trophic linkages among kelp, seagrass, and several herbivorous and carnivorous species, including rockfish. We used stable isotopes of carbon and nitrogen to estimate the kelp- and eelgrass-derived isotope contributions to invertebrate and fish tissue. Understanding these connections, and their strengths, is necessary for effective management and recovery. In this presentation we will place our findings in the context of ongoing kelp recovery plans

Five decades of change in somatic growth of Pacific hake from Puget Sound and Strait of Georgia

Declines in fish body size have been reported in many populations and these changes likely have important ramifications for the sustainability of harvested species and ecosystem function. Pacific hake, Merluccius productus, have shown declines in size over the last several decades for populations located in Puget Sound (PS), Washington, USA, and Strait of Georgia (SoG), British Columbia, Canada. To examine this decrease in size, we used archived otoliths from both populations to assess when the decrease in somatic growth occurred and explored what factors and processes might explain the decline, including otolith microchemistry to infer the environment experienced by fish at different ages. Results indicated that substantial changes in juvenile somatic growth have occurred across decades. The divergence in body size occurred in the second summer, whereby SoG fish grew, on average, 18% more than PS fish. Within the PS population, somatic growth differed significantly among fish that hatched in the 1980s, 1990s, and 2010s, such that the more recently hatched fish grew 26% more in their first summer and 71% less in their second summer relative to those that hatched in the 1980s. In comparison, growth of SoG fish did not differ between those that hatched in 1970s and 1990s. For both populations growth in the first and third summer was positively and negatively related, respectively, to the abundance of harbor seals, while growth in the first and second summer was negatively related to salinity. Overall, this study highlights the complicated nature of Pacific hake population recovery under dynamic, and typically uncontrollable, variation in biotic and abiotic conditions

What did you say about my mother? The complexities of maternally derived chemical signatures in otoliths.

Connecting maternal migratory behavior with the behavior and ecology of their progeny can reveal important details in the ecology of a population. One method for linking maternal migration to early juvenile life-history is through maternal chemistry recorded in otoliths. Despite the wide use of maternal signatures to infer anadromy, the duration and dynamics of maternal otolith signatures are not well understood. Shifts in the elemental ratios and strontium isotope (The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

An estimation method of surface defects of LMJ microshells

This article presents a radiographic characterization method for microshells. In the LMJ (Laser Mega-Joule) framework, microshells are tiny plastic objects used in power laser experiments of inertial fusion. These microshells are characterized by low energy radiography. On the microshell radiographs, a phenomenon of phase contrast is observed. The origin of this phenomenon has been identied as sharp variation of amplitude due to refraction. Theoretical model links pixel information with microshell geometry. These points are used for a contour detection. Finally, an estimation of surface defects described by spherical harmonics is done