Sea urchin spines protect the animal's body from predators and from the effect of high energy... more Sea urchin spines protect the animal's body from predators and from the effect of high energy environments. The spines of urchins from different orders, families and genera have very different sizes, morphologies and microarchitectures, and the different designs of sea urchin spines reveal much about the design space available for functional biogenic calcite-based structures. The 3D microarchitecture of primary spines of a number of sea urchins was studied with synchrotron microCT and reconstructed with 5 μm or smaller voxels (volume elements), and similarities and differences were determined in order to better understand the design space. Hollow spines from different genera of the family Diadematidae, order Diadematoida, are one type of solution, but significant differences were observed within this phylogenic subset. Spines from members of order Echinoidea, family Toxopneustidae, employ a very different strategy, one that emphasizes interconnected trabeculae to a greater degree than do the diadematids. Numerical data for some 3D structural characteristics are presented, data that would be impractical to obtain by methods other than microCT.
ABSTRACT Densities of vegetative propagules (joints) of two cactus species (cylindropuntias) were... more ABSTRACT Densities of vegetative propagules (joints) of two cactus species (cylindropuntias) were manipulated in an experiment in the Lower Colorado Desert (Sonoran) of southern California and observations were made from 1981 to 1999. Stem joints of Cylindropuntia bigelovii break off easily and are the sole means of reproduction. Cylindropuntia echinocarpa reproduces primarily by sexual means but has been reported to have a low rate of asexual reproduction by detached joints. The experiment tested 3 predictions: (1) because of its usual asexual mode of reproduction, C. bigelovii would have better establishment success than the vegetative parts of C. echinocarpa; (2) because areas occupied by C. bigelovii often are densely carpeted with joints, this species would be more density-tolerant than would C. echinocarpa; (3) the more tolerant species should show the slowest growth. Overall, results were contrary to these predictions: survival of C. bigelovii showed a clear density effect but C. echinocarpa did not and the more tolerant species, C. echinocarpa, also showed better growth. At the end of 16 years, however, both species had similar numbers of survivors.
Dead and downed ocotillos (Fouquieria splendens) are common in the Colorado Desert of southern Ca... more Dead and downed ocotillos (Fouquieria splendens) are common in the Colorado Desert of southern California and pose a question concerning the life-span of adult plants that have been reported to be long-lived: if ocotillo is long-lived, decay rates must be very slow. Our study focused on decomposition and disintegration of above-ground ocotillo wood over 14 years to obtain a rate of change in dead mass. Disintegration rate was used in a new application of life-cycle graph analysis to calculate persistence time of carcasses, which in turn was used to estimate adult survival rates. We conclude that previous estimates of life spans may be too conservative and half-life of adult shrubs is over 200 years. Our approach to estimating adult survival from decay rates provides an independent test of survival transitions based on live plants for some species and so is an additional tool for developing life cycle models.
ABSTRACT Total body size, mass or linear measurements, and gonad mass or volumes have been record... more ABSTRACT Total body size, mass or linear measurements, and gonad mass or volumes have been recorded for the North American Pacific coast sea urchins Strongylocentrotus purpuratus, Mesocentrotus (Strongylocentrotus) franciscanus, and Lytechinus pictus by various workers at diverse sites and for varying lengths of time from 1954 to 2009. Some dissections included other body components such as the gut, body wall, and Aristotle’s lantern, and some dissections included both wet and dry mass. There are numerous peer-reviewed publications that have used some of these data, but some data have appeared only in graduate theses or in the gray literature. There also are data that have never appeared outside the original data sheets. Historically, data were used to describe reproductive cycles and then to compare responses to stressors such as food limitation or pollution. Differences in temperature among sites also have been explored. More recently, dissection data have linked gonad development to ocean conditions, so called bottom-up forcing. The data set presented here is a historical record of gonad development for a common group of marine invertebrates in intertidal and nearshore environments, which can be used to test hypotheses concerning future changes associated with climate change and ocean acidification along the Pacific Coast of North America.
A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as p... more A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as primary routes for lunar processing. Most of these have not been studied in sufficient detail to permit reliable plant mass estimates. An even broader range of possible technologies exists for Marian resource utilization. A methodology for screening and final selection of candidate processes is proposed to ensure timely development of practical technology to support the general goals of the space exploration initiative. This consists of a 3-component rating system based on benefit, cost, and risk variables. Benefits include the nature, diversity and yield of products. The relative values of propellants and non-propellant products may be expected to change as lunar or planetary exploration & base programs mature. Cost factors include facility specific mass, development and transport costs, and deployment & operational manpower requirements. Risk factors may be expressed in terms of forecast values for plant availability and expected lifetimes. These parameters are subject to improvement through R&D. Parameter definitions and qualitative assessments for candidate processes are presented. The current data base is insufficient to support final process selection.
A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as p... more A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as primary routes for lunar processing. Most of these have not been studied in sufficient detail to permit reliable plant mass estimates. An even broader range of possible technologies exists for Marian resource utilization. A methodology for screening and final selection of candidate processes is proposed to ensure timely development of practical technology to support the general goals of the space exploration initiative. This consists of a 3-component rating system based on benefit, cost, and risk variables. Benefits include the nature, diversity and yield of products. The relative values of propellants and non-propellant products may be expected to change as lunar or planetary exploration & base programs mature. Cost factors include facility specific mass, development and transport costs, and deployment & operational manpower requirements. Risk factors may be expressed in terms of forecast values for plant availability and expected lifetimes. These parameters are subject to improvement through R&D. Parameter definitions and qualitative assessments for candidate processes are presented. The current data base is insufficient to support final process selection.
Sea urchin spines protect the animal's body from predators and from the effect of high energy... more Sea urchin spines protect the animal's body from predators and from the effect of high energy environments. The spines of urchins from different orders, families and genera have very different sizes, morphologies and microarchitectures, and the different designs of sea urchin spines reveal much about the design space available for functional biogenic calcite-based structures. The 3D microarchitecture of primary spines of a number of sea urchins was studied with synchrotron microCT and reconstructed with 5 μm or smaller voxels (volume elements), and similarities and differences were determined in order to better understand the design space. Hollow spines from different genera of the family Diadematidae, order Diadematoida, are one type of solution, but significant differences were observed within this phylogenic subset. Spines from members of order Echinoidea, family Toxopneustidae, employ a very different strategy, one that emphasizes interconnected trabeculae to a greater degree than do the diadematids. Numerical data for some 3D structural characteristics are presented, data that would be impractical to obtain by methods other than microCT.
ABSTRACT Densities of vegetative propagules (joints) of two cactus species (cylindropuntias) were... more ABSTRACT Densities of vegetative propagules (joints) of two cactus species (cylindropuntias) were manipulated in an experiment in the Lower Colorado Desert (Sonoran) of southern California and observations were made from 1981 to 1999. Stem joints of Cylindropuntia bigelovii break off easily and are the sole means of reproduction. Cylindropuntia echinocarpa reproduces primarily by sexual means but has been reported to have a low rate of asexual reproduction by detached joints. The experiment tested 3 predictions: (1) because of its usual asexual mode of reproduction, C. bigelovii would have better establishment success than the vegetative parts of C. echinocarpa; (2) because areas occupied by C. bigelovii often are densely carpeted with joints, this species would be more density-tolerant than would C. echinocarpa; (3) the more tolerant species should show the slowest growth. Overall, results were contrary to these predictions: survival of C. bigelovii showed a clear density effect but C. echinocarpa did not and the more tolerant species, C. echinocarpa, also showed better growth. At the end of 16 years, however, both species had similar numbers of survivors.
Dead and downed ocotillos (Fouquieria splendens) are common in the Colorado Desert of southern Ca... more Dead and downed ocotillos (Fouquieria splendens) are common in the Colorado Desert of southern California and pose a question concerning the life-span of adult plants that have been reported to be long-lived: if ocotillo is long-lived, decay rates must be very slow. Our study focused on decomposition and disintegration of above-ground ocotillo wood over 14 years to obtain a rate of change in dead mass. Disintegration rate was used in a new application of life-cycle graph analysis to calculate persistence time of carcasses, which in turn was used to estimate adult survival rates. We conclude that previous estimates of life spans may be too conservative and half-life of adult shrubs is over 200 years. Our approach to estimating adult survival from decay rates provides an independent test of survival transitions based on live plants for some species and so is an additional tool for developing life cycle models.
ABSTRACT Total body size, mass or linear measurements, and gonad mass or volumes have been record... more ABSTRACT Total body size, mass or linear measurements, and gonad mass or volumes have been recorded for the North American Pacific coast sea urchins Strongylocentrotus purpuratus, Mesocentrotus (Strongylocentrotus) franciscanus, and Lytechinus pictus by various workers at diverse sites and for varying lengths of time from 1954 to 2009. Some dissections included other body components such as the gut, body wall, and Aristotle’s lantern, and some dissections included both wet and dry mass. There are numerous peer-reviewed publications that have used some of these data, but some data have appeared only in graduate theses or in the gray literature. There also are data that have never appeared outside the original data sheets. Historically, data were used to describe reproductive cycles and then to compare responses to stressors such as food limitation or pollution. Differences in temperature among sites also have been explored. More recently, dissection data have linked gonad development to ocean conditions, so called bottom-up forcing. The data set presented here is a historical record of gonad development for a common group of marine invertebrates in intertidal and nearshore environments, which can be used to test hypotheses concerning future changes associated with climate change and ocean acidification along the Pacific Coast of North America.
A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as p... more A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as primary routes for lunar processing. Most of these have not been studied in sufficient detail to permit reliable plant mass estimates. An even broader range of possible technologies exists for Marian resource utilization. A methodology for screening and final selection of candidate processes is proposed to ensure timely development of practical technology to support the general goals of the space exploration initiative. This consists of a 3-component rating system based on benefit, cost, and risk variables. Benefits include the nature, diversity and yield of products. The relative values of propellants and non-propellant products may be expected to change as lunar or planetary exploration & base programs mature. Cost factors include facility specific mass, development and transport costs, and deployment & operational manpower requirements. Risk factors may be expressed in terms of forecast values for plant availability and expected lifetimes. These parameters are subject to improvement through R&D. Parameter definitions and qualitative assessments for candidate processes are presented. The current data base is insufficient to support final process selection.
A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as p... more A recent survey paper on lunar manufacturing identified 26 initial steps previously proposed as primary routes for lunar processing. Most of these have not been studied in sufficient detail to permit reliable plant mass estimates. An even broader range of possible technologies exists for Marian resource utilization. A methodology for screening and final selection of candidate processes is proposed to ensure timely development of practical technology to support the general goals of the space exploration initiative. This consists of a 3-component rating system based on benefit, cost, and risk variables. Benefits include the nature, diversity and yield of products. The relative values of propellants and non-propellant products may be expected to change as lunar or planetary exploration & base programs mature. Cost factors include facility specific mass, development and transport costs, and deployment & operational manpower requirements. Risk factors may be expressed in terms of forecast values for plant availability and expected lifetimes. These parameters are subject to improvement through R&D. Parameter definitions and qualitative assessments for candidate processes are presented. The current data base is insufficient to support final process selection.
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