989 resultados para 341.753
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Eguíluz, Federico; Merino, Raquel; Olsen, Vickie; Pajares, Eterio; Santamaría, José Miguel (eds.)
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This study analyzed species richness, distribution, and sighting frequency of selected reef fishes to describe species assemblage composition, abundance, and spatial distribution patterns among sites and regions (Upper Keys, Middle Keys, Lower Keys, and Dry Tortugas) within the Florida Keys National Marine Sanctuary (FKNMS) barrier reef ecosystem. Data were obtained from the Reef Environmental Education Foundation (REEF) Fish Survey Project, a volunteer fish-monitoring program. A total of 4,324 visual fish surveys conducted at 112 sites throughout the FKNMS were used in these analyses. The data set contained sighting information on 341 fish species comprising 68 families. Species richness was generally highest in the Upper Keys sites (maximum was 220 species at Molasses Reef) and lowest in the Dry Tortugas sites. Encounter rates differed among regions, with the Dry Tortugas having the highest rate, potentially a result of differences in the evenness in fishes and the lower diversity of habitat types in the Dry Tortugas region. Geographic coverage maps were developed for 29 frequently observed species. Fourteen of these species showed significant regional variation in mean sighting frequency (%SF). Six species had significantly lower mean %SF and eight species had significantly higher mean %SF in the Dry Tortugas compared with other regions. Hierarchical clustering based on species composition (presence-absence) and species % SF revealed interesting patterns of similarities among sites that varied across spatial scales. Results presented here indicate that phenomena affecting reef fish composition in the FKNMS operate at multiple spatial scales, including a biogeographic scale that defines the character of the region as a whole, a reef scale (~50-100 km) that include meso-scale physical oceanographic processes and regional variation in reef structure and associated reef habitats, and a local scale that includes level of protection, cross-shelf location and a suite of physical characteristics of a given reef. It is likely that at both regional and local scales, species habitat requirements strongly influence the patterns revealed in this study, and are particularly limiting for species that are less frequently observed in the Dry Tortugas. The results of this report serve as a benchmark for the current status of the reef fishes in the FKNMS. In addition, these data provide the basis for analyses on reserve effects and the biogeographic coupling of benthic habitats and fish assemblages that are currently underway. (PDF contains 61 pages.)
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Table of Contents
1 | Introduction | 1 |
1.1 | What is an Adiabatic Shear Band? | 1 |
1.2 | The Importance of Adiabatic Shear Bands | 6 |
1.3 | Where Adiabatic Shear Bands Occur | 10 |
1.4 | Historical Aspects of Shear Bands | 11 |
1.5 | Adiabatic Shear Bands and Fracture Maps | 14 |
1.6 | Scope of the Book | 20 |
2 | Characteristic Aspects of Adiabatic Shear Bands | 24 |
2.1 | General Features | 24 |
2.2 | Deformed Bands | 27 |
2.3 | Transformed Bands | 28 |
2.4 | Variables Relevant to Adiabatic Shear Banding | 35 |
2.5 | Adiabatic Shear Bands in Non-Metals | 44 |
3 | Fracture and Damage Related to Adiabatic Shear Bands | 54 |
3.1 | Adiabatic Shear Band Induced Fracture | 54 |
3.2 | Microscopic Damage in Adiabatic Shear Bands | 57 |
3.3 | Metallurgical Implications | 69 |
3.4 | Effects of Stress State | 73 |
4 | Testing Methods | 76 |
4.1 | General Requirements and Remarks | 76 |
4.2 | Dynamic Torsion Tests | 80 |
4.3 | Dynamic Compression Tests | 91 |
4.4 | Contained Cylinder Tests | 95 |
4.5 | Transient Measurements | 98 |
5 | Constitutive Equations | 104 |
5.1 | Effect of Strain Rate on Stress-Strain Behaviour | 104 |
5.2 | Strain-Rate History Effects | 110 |
5.3 | Effect of Temperature on Stress-Strain Behaviour | 114 |
5.4 | Constitutive Equations for Non-Metals | 124 |
6 | Occurrence of Adiabatic Shear Bands | 125 |
6.1 | Empirical Criteria | 125 |
6.2 | One-Dimensional Equations and Linear Instability Analysis | 134 |
6.3 | Localization Analysis | 140 |
6.4 | Experimental Verification | 146 |
7 | Formation and Evolution of Shear Bands | 155 |
7.1 | Post-Instability Phenomena | 156 |
7.2 | Scaling and Approximations | 162 |
7.3 | Wave Trapping and Viscous Dissipation | 167 |
7.4 | The Intermediate Stage and the Formation of Adiabatic Shear Bands | 171 |
7.5 | Late Stage Behaviour and Post-Mortem Morphology | 179 |
7.6 | Adiabatic Shear Bands in Multi-Dimensional Stress States | 187 |
8 | Numerical Studies of Adiabatic Shear Bands | 194 |
8.1 | Objects, Problems and Techniques Involved in Numerical Simulations | 194 |
8.2 | One-Dimensional Simulation of Adiabatic Shear Banding | 199 |
8.3 | Simulation with Adaptive Finite Element Methods | 213 |
8.4 | Adiabatic Shear Bands in the Plane Strain Stress State | 218 |
9 | Selected Topics in Impact Dynamics | 229 |
9.1 | Planar Impact | 230 |
9.2 | Fragmentation | 237 |
9.3 | Penetration | 244 |
9.4 | Erosion | 255 |
9.5 | Ignition of Explosives | 261 |
9.6 | Explosive Welding | 268 |
10 | Selected Topics in Metalworking | 273 |
10.1 | Classification of Processes | 273 |
10.2 | Upsetting | 276 |
10.3 | Metalcutting | 286 |
10.4 | Blanking | 293 |
Appendices | 297 | |
A | Quick Reference | 298 |
B | Specific Heat and Thermal Conductivity | 301 |
C | Thermal Softening and Related Temperature Dependence | 312 |
D | Materials Showing Adiabatic Shear Bands | 335 |
E | Specification of Selected Materials Showing Adiabatic Shear Bands | 341 |
F | Conversion Factors | 357 |
References | 358 | |
Author Index | 369 | |
Subject Index | 375 |
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The status of the Gulf menhaden, Brevoortia patronus, fishery was assessed with purse-seine landings data from 1946 to 1997 and port sampling data from 1964 to 1997. These data were analyzed to determine growth rates, biological reference points for fi shing mortality from yield per recruit and maximum spawning potential analyses, spawner-recruit relationships, and maximum sustainable yield (MSY). The separable virtual population approach was used for the period 1976–97 (augmented by earlier analyses for 1964–75) to obtain point estimates of stock size, recruits to age 1, spawning stock size, and fishing mortality rates. Exploitation rates for age-1 fi sh ranged between 11% and 45%, for age-2 fi sh between 32% and 72%, and for age-3 fi sh between 32% and 76%. Biological reference points from yield per recruit (F0.1: 1.5–2.5/yr) and spawning potential ratio (F20: 1.3–1.9/yr and F30: 0.8–1.2/yr) were obtained for comparison with recent estimates of F (0.6–0.8/yr). Recent spawning stock estimates (as biomass or eggs) are above the long-term average, while recent recruits to age 1 are comparable to the long-term average. Parameters from Ricker-type spawner-recruit relations were estimated, although considerable unexplained variability remained. Recent survival to age-1 recruitment has generally been below that expected based on the Ricker spawner-recruit relation. Estimates of long-term MSY from PRODFIT and ASPIC estimation of production model ranged between 717,000 t and 753,000 t, respectively. Declines in landings between 1988 and 1992 raised concerns about the status of the Gulf menhaden stock. Landings have fl uctuated without trend since 1992, averaging about 571,000 t. However, Gulf menhaden are short lived and highly fecund. Thus, variation in recruitment to age 1, largely mediated by environmental conditions, infl uences fi shing success over the next two years (as age-1 and age-2 fi sh). Comparisons of recent estimates of fi shing mortality to biological reference points do not suggest overfishing. (PDF file contains 22 pages.)
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ENGLISH: Yellowfin and skipjack tuna occur in commercial quantities in the Eastern Pacific Ocean from California to Chile. They are captured in the high seas at distances from the mainland up to several hundred miles (see Alverson, 1960). The Inter-American Tropical Tuna Commission has been engaged for several years in research on the biology, ecology, and population dynamics of the stocks of these species supporting the commercial fishery, in order to elucidate the effects of the fishery and of fishery independent factors on their abundance and behavior, to provide the scientific basis for rational management of the fishery. An important aspect of this research is the investigation of the migrations of these species in the Eastern Pacific, and the determination of whether each consists of but a single population or is composed of various sub-populations. One direct means of approaching these problems is the tagging, and subsequent recovery, of specimens in the region of the commercial fishery. This also provides direct information on growth rates, by comparison of sizes of specimens at tagging and upon later recovery, and can furnish the basis of estimating rates of mortality. These are two of the important elements of the vital statistics of the tuna populations. SPANISH: El atún aleta amarilla y el barrilete se encuentran en cantidades comerciales en el Océano Pacífico Oriental, desde California hasta Chile. Estos peces son capturados en alta mar a varios cientos de millas de distancia de tierra firme (ver Alverson, 1960). La Comisión Interamericana del Atún Tropical ha estado dedicada durante varios años a la investigación de la biología, ecología y dinámica de las poblaciones de los stocks de las indicadas especies que mantienen la pesquería comercial, a fin de elucidar los efectos de ésta y de los factores independientes de la explotación sobre la abundancia y hábitos de estos peces, para obtener una base científica que permita una administración racional de la pesquería. Un aspecto importante de esta investigación es el estudio de los movimientos migratorios de estas especies en el Pacífico Oriental, y la determinación de que si cada una constituye una sola población o está compuesta de varias subpoblaciones. Un medio directo de abordar estos problemas es el de la marcación, y subsecuente recuperación, de especímenes en la región de la pesquería comercial. Esto también proporciona una información directa sobre la tasa de crecimiento, por la comparación de los tamaños de los especímenes al ser marcados y recuperados más tarde y puede proveer la base para estimar las tasas de mortalidad. Estos son dos de los elementos importantes de las estadísticas vitales de las poblaciones de atún.
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V, 341 p.
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341 p.
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In this work, a simple correlation, which incorporates the mixture velocity, drift velocity, and the correction factor of Farooqi and Richardson, was proposed to predict the void fraction of gas/non-Newtonian intermittent flow in upward inclined pipes. The correlation was based on 352 data points covering a wide range of flow rates for different CMC solutions at diverse angles. A good agreement was obtained between the predicted and experimental results. These results substantiated the general validity of the model presented for gas/non-Newtonian two-phase intermittent flows.
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Since 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gearSince 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gear. (PDF contains 44 pages)