279 research outputs found
William Cobbett, author of the Political Register [picture]
No full textFacsimile autograph: Wm. Cobbett.; Catalogue of engraved British portraits; engraved by D. Maclise.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.pic-an9351838; Rex Nan Kivell Collection NK10965.; U6467
El cambio social
No full textThe concept of social change refers to alterations and modifications in the social behavior and the cultural values of determinated social systems and structures. In opposition to the so called social progress, social change has no teologic meaning. Social system means a structure of social processes and relations showing some regularity. The dichotomy between social statics (structures) and social dynamics (change) is therefore incorrect, because the first does not exist in reality. Cultural changes are but functions of the social changes. Among the functions which are contributions of a social system to the fundamental needs of its members to a more inclusive social system, the author distinguishes actual functions, latent or not evident functions and disfunctions (of negative effect). With regard to causation, the author points out MAV IVER\u27s classification into distributive, collective and conjunctural phenomena. To forecast and control socio-cultural phenomena, a scientific methods is necessary. After pointing out the conditions for a correct scientific methodology, the author explains the modern complementary and qualitative trends: typology, the same combined with psychology and cultural anthropology and the "functional process", which reduces social change to a manageable analytical process. Finally, he examines five basic aspects of the social change process: social deviations, innovations, the innovation valuating process the transition phase and the institutionalization processThe concept of social change refers to alterations and modifications in the social behavior and the cultural values of determinated social systems and structures. In opposition to the so called social progress, social change has no teologic meaning. Social system means a structure of social processes and relations showing some regularity. The dichotomy between social statics (structures) and social dynamics (change) is therefore incorrect, because the first does not exist in reality. Cultural changes are but functions of the social changes. Among the functions which are contributions of a social system to the fundamental needs of its members to a more inclusive social system, the author distinguishes actual functions, latent or not evident functions and disfunctions (of negative effect). With regard to causation, the author points out MAV IVER\u27s classification into distributive, collective and conjunctural phenomena. To forecast and control socio-cultural phenomena, a scientific methods is necessary. After pointing out the conditions for a correct scientific methodology, the author explains the modern complementary and qualitative trends: typology, the same combined with psychology and cultural anthropology and the "functional process", which reduces social change to a manageable analytical process. Finally, he examines five basic aspects of the social change process: social deviations, innovations, the innovation valuating process the transition phase and the institutionalization proces
Tyrannosaurus rex Osborn 1905
No full textWhether Tyrannosaurus rex was likely to have found food primarily by predation or scavenging has been debated for close to a century without resolution (Erickson et al. 1996; Erickson 1999). Much of this debate has used arguments based on jaw morphology and dentition. Here, we use calculations of energy gains and losses to estimate the minimum carrion productivity an ecosystem must provide in order to support an obligate scavenger of the 6 tonne (6000 kg) mass of T. rex. Our estimates suggest that carrion productivity equivalent to the current Serengeti would have been sufficient to support such a scavenger. Hence, we argue on the basis of physiological ecology that T. rex need not have been an active predator and could have found sufficient food to support itself purely by scavenging. Our hypothesis is that the key constraint for scavengers is generally their ability to find food items. This is in contrast to predators, where capturing rather than discovering prey is the key constraint, and herbivores, where processing consumed food is often the key restriction on energy gain rate. We assume that the scavenger spends a constant fraction (a) of its time searching for food items that are distributed with a constant uniform density (f). If, when active, the scavenger searches out area at a rate V, then it finds food items at a rate a fV. We assume that it extracts an amount of energy E from each food item found. Hence, the rate of energy gathering (E in) is a f VE. We assume that the individual has a resting metabolic rate R, but that searching for food requires extra energy investment at rate S. Thus, the rate of energy expenditure (E o ut) is given by R + a S, and scavengers attempt to optimize net energy gain (E net) given by E n et = E in ‾ E o ut = a(f VE ‾ S) ‾ R. (2.1) If we demand that E net be positive then we can rearrange equation (2.1) as a restriction on the energy density of food available for scavenging: for a positive energy budget we demand that the density of food energy available to a scavenger is greater than a critical value given by a S + R f E m in =. a V (2.2) The right-hand side of this is the minimum energy density that an ecosystem needs to have to support a scavenger. We will now estimate this for a scavenging T. rex and compare this with the energy density of carrion in the extant Serengeti. We will assume that restrictions owing to nightfall, bad weather and sleep mean that on average the scavenger can actively seek food for 50% of the 24 hour day, so we set a = 0.5. The relationship between the mass M of a reptile in kilograms and the resting metabolic rate R in watts has been described by Schmidt-Nielson (1984) R = 0.38 M 0.83. (2.3) There have been various estimates of the live mass of a full-sized T. rex, ranging from 3000 to 8000 kg (Farlow et al. 1995; Christiansen 1997; Seebacher 2001). Recent papers seem to be converging towards estimates close to 6 tonnes, so we will use a value of 6000 kg throughout this paper. Substituting this into equation (2.3) gives a value for R of 520 W. The relationship between the mass M of an ectotherm (in kg), the speed of travel v (in m s ‾1) and the extra cost of travel S (in W) has been suggested by Bennett (1982) to be S = 10.3 vM 0.64. (2.4) Reptiles can sustain a speed equivalent to 10% of their maximum speed (Bennett & Ruben 1979). The maximum speed of equivalent-sized mammals and reptiles is similar (Bennett & Ruben 1979). The following relationship between mass M (in kg) and maximum speed v m ax (in m s ‾1) has been proposed by Alexander (1977): v m ax = 8.5 M ‾ 0.08. (2.5) Substituting M = 6000 in equation (2.5) gives a maximum speed for a T. rex of 4.2 m s ‾ 1. This compares well with a recent estimate of 5 m s ‾1 based on T. rex ’s limb mor- * Author for correspondence ([email protected]). phology (Hutchinson & Garcia 2002). We will assume that sustained travelling speed, v, is 10% of our estimate, i.e. 0.42 m s ‾ 1. If we substitute for v and M in equation (2.4), then this gives an added cost of travel S of 1100 W. The rate at which an area is swept, V, is simply the sustained travel speed v multiplied by twice the distance at which food can be detected, which we will denote d. That is V = 0.84 d. (2.6) Substituting the parameter values derived in equation (2.6) into equation (2.2) gives an equation for the minimum energy density of carrion (in J m ‾2) that could sustain an animal (fE m in) in terms of the distance at which it could detect carrion (d) as follows: 2550 f E m in =. d (2.7) This relationship is plotted for a range of d values from 10 m to 10 km in figure 1. To give us something to compare this against, we can estimate the energy density of carrion available each day from ungulate herbivores in the modern Serengeti ecosystem. It has been estimated that a total weight of 4´ 107 kg of ungulates die in the Serengeti each year (Houston 1979). Assuming that these have an mass-specific energy content of 7´ 106 J kg ‾1 (Peters 1983), and that the Serengeti stretches over 25 000 km 2 (Sinclair & Norton-Griffiths 1979). This gives a mean energy density of 31 J m ‾ 2 d ‾1. When we compare this value with figure 1, we see that even if we make the conservative assumption that animals that die only remain available to T. rex for 24 hours (before spoiling or being consumed by other scavengers), then, if it is able to monopolize all the food it finds and can detect food at a range of 80 m, an ecosystem of similar productivity to the current Serengeti would provide sufficient food for such a scavenger. One reason for caution in the interpretation of our results is that the allometric relations used are based on data from extant reptiles, and consequently very few of the species used to generate the relations would have a mass approaching even 1% of our estimated mass for T. rex. Of our estimates, the sustainable travel speed of 0.42 m s ‾ 1 seems rather low for a bipedal animal with 2.5 m legs (see Fitzgerald (2002) and references therein). If we repeat our calculations assuming a sustainable running speed of 2.1 m s ‾ 1, then this changes equation (2.7) to 1600 f E m in =. d (2.8) The faster running speed increases the area that can be swept for food faster than it increases the total energetic requirements of that animal, and so this leads to a reduction in the food density required to sustain the scavenger. Thus, our initial assumption of a low running speed can be seen as conservative, making a scavenging lifestyle challenging to maintain. Some scientists consider that mammals (rather than reptiles) are a more appropriate model for dinosaurs (e.g. Bakker 2001). It is possible to repeat our calculations under such an assumption. Schmidt-Nielson (1984) suggests that this would change our equation for R to R = 0.38 M 0.83, (2.9) increasing R substantially to 2300 W for our 6000 kg animal. Calder (1996) suggests that, for a mammal, the equation for S becomes S = 10.7 vM 0.68. (2.10) Bennett & Ruben (1979) suggest that the sustainable speed of mammals is 50% of their maximum speed, hence we will assume that v is 2.1 m s ‾1. If we finally assume that a is unchanged at 0.5, then (using mammals rather than reptiles as a model) changes equation (2.7) to 3100 f E m in =. d (2.11) Hence, we see that substantial compensation for higher resting and movement costs in a mammal-like T. rex may come from a mammalian physiology allowing a higher sustainable rate of movement. The consequence of this is that the minimum food density required by our scavenger is only slightly increased if a mammalian model rather than a reptilian model is assumed. 3. CONCLUSIONS Our calculation suggests that T. rex would be able to gather enough food to survive as a pure scavenger if a number of conditions are met. One is that the ecosystem yields the same density of carrion as the current Serengeti. Estimates of primary productivity at the place and time appropriate to T. rex vary widely but encompass values similar to that of the present-day Serengeti (Beerling & Woodward 2001). Any given primary productivity would have supported a greater biomass of ectothermic dinosaurs compared to the endothermic mammals that dominate the extant Serengeti (Farlow 1990). This higher biomass will more than compensate for the lower turnover rate per unit biomass that one would predict if dinosaurian herbivores had longer lifespans than the mammalian herbivores of the extant Serengeti, on account both of their larger size and probably lower specific metabolic rates. Another condition is that T. rex can detect carcasses at a distance of 80 m. Given the performance of polar bears in detecting seals over distances of kilometres (Stirling 1977) and the ability of turkey vultures to find 80% of experimentally provided chicken carcasses in tropical rainforest within 12 hours of presentation (Houston 1986), this seems likely to have been comfortably within T. rex ’s compass. Brochu (2000) argues, on the basis of computed tomographic analysis of a fossil skull, that T. rex had greatly enlarged olfactory bulbs, suggestive of high olfactory acuity. Farlow (1994) suggests that the upright stance of T. rex could have aided carrion location, both by visual and olfactory pathways. We also assumed that the fallen carcass was only detectable to T. rex for a period of 24 hours. Little is known about how long a carcass is accessible to vertebrate scavenges. Small (chicken) carcasses in tropical African forests were totally consumed by maggots within 3 days (Houston 1987). Hence, our assumption that prey is only available for 1 day seems entirely reasonable, and if anything on the low side. Our final assumption that our focal T. rex individual is able to find all the carcasses that fall in areas where it searches seems less plausible. It is likely that our T. rex would experience competition from other species and from other members of its own species. However, if we arbitrarily assume that our focal individual is only able to access 25% of the carcasses that fall, so that the ecosystem has effectively only 25% of the carrion density of the Serengeti (7.75 J m ‾2), then (from figure 1) we see that T. rex would have to be able to detect prey at a distance of 330 m to balance its energy budget. This is more challenging, but still seems within the bounds of the possible, especially if, like many extant reptiles (Zug et al. 2001), T. rex had an effective sense of smell. Hence, our conclusion is that an energy budget analysis suggests that a reptile as large as T. rex could have survived using a purely scavenging lifestyle, providing that competition for carrion was low. This conclusion leads to the obvious question, why is there not a T. rex- like scavenger on the Serengeti today? Or generally, we must ask why vultures are the only extant vertebrates that have a predominantly scavenging lifestyle. The answer may be that an avian scavenger can outcompete a terrestrial one because, as mentioned in § 1, the key requirement for a scavenger is to minimize energy expenditure while searching. Compared to terrestrial locomotion, even powered flying is faster and much less energetically expensive per distance covered (Schmidt- Nielson 1984), and birds like vultures that make extensive use of soaring have dramatically lower energy expenditure than any terrestrial scavenger could have. If T. rex was a scavenger, then this was probably only possible because avian radiation had yet to have a substantial effect on ecosystems. It may well be, as suggested by Farlow (1994), that T. rex was an opportunist flesh eater, combining scavenging carrion with active predation. That said, our calculations suggest that total (or near total) dependence on carrion (in the manner of extant vultures) may at least have been feasible. a S + R f E m in =. a V (2.2) The right-hand side of this is the minimum energy density that an ecosystem needs to have to support a scavenger. We will now estimate this for a scavenging T. rex and compare this with the energy density of carrion in the extant Serengeti. We will assume that restrictions owing to nightfall, bad weather and sleep mean that on average the scavenger can actively seek food for 50% of the 24 hour day, so we set a = 0.5. The relationship between the mass M of a reptile in kilograms and the resting metabolic rate R in watts has been described by Schmidt-Nielson (1984) R = 0.38 M 0.83. (2.3) There have been various estimates of the live mass of a full-sized T. rex, ranging from 3000 to 8000 kg (Farlow et al. 1995; Christiansen 1997; Seebacher 2001). Recent papers seem to be converging towards estimates close to 6 tonnes, so we will use a value of 6000 kg throughout this paper. Substituting this into equation (2.3) gives a value for R of 520 W. The relationship between the mass M of an ectotherm (in kg), the speed of travel v (in m s ‾1) and the extra cost of travel S (in W) has been suggested by Bennett (1982) to be S = 10.3 vM 0.64. (2.4) Reptiles can sustain a speed equivalent to 10% of their maximum speed (Bennett & Ruben 1979). The maximum speed of equivalent-sized mammals and reptiles is similar (Bennett & Ruben 1979). The following relationship between mass M (in kg) and maximum speed v m ax (in m s ‾1) has been proposed by Alexander (1977): v m ax = 8.5 M ‾ 0.08. (2.5) Substituting M = 6000 in equation (2.5) gives a maximum speed for a T. rex of 4.2 m s ‾ 1. This compares well with a recent estimate of 5 m s ‾1 based on T. rex ’s limb mor- * Author for correspondence ([email protected]). phology (Hutchinson & Garcia 2002). We will assume that sustained travelling speed, v, is 10% of our estimate, i.e. 0.42 m s ‾ 1. If we substitute for v and M in equation (2.4), then this gives an added cost of travel S of 1100 W. The rate at which an area is swept, V, is simply the sustained travel speed v multiplied by twice the distance at which food can be detected, which we will denote d. That is V = 0.84 d. (2.6) Substituting the parameter values derived in equation (2.6) into equation (2.2) gives an equation for the minimum energy density of carrion (in J m ‾2) that could sustain an animal (fE m in) in terms of the distance at which it could detect carrion (d) as follows: 2550 f E m in =. d (2.7) This relationship is plotted for a range of d values from 10 m to 10 km in figure 1. To give us something to compare this against, we can estimate the energy density of carrion available each day from ungulate herbivores in the modern Serengeti ecosystem. It has been estimated that a total weight of 4´ 107 kg of ungulates die in the Serengeti each year (Houston 1979). Assuming that these have an mass-specific energy content of 7´ 106 J kg ‾1 (Peters 1983), and that the Serengeti stretches over 25 000 km 2 (Sinclair & Norton-Griffiths 1979). This gives a mean energy density of 31 J m ‾ 2 d ‾1. When we compare this value with figure 1, we see that even if we make the conservative assumption that animals that die only remain available to T. rex for 24 hours (before spoiling or being consumed by other scavengers), then, if it is able to monopolize all the food it finds and can detect food at a range of 80 m, an ecosystem of similar productivity to the current Serengeti would provide sufficient food for such a scavenger. One reason for caution in the interpretation of our results is that the allometric relations used are based on data from extant reptiles, and consequently very few of the species used to generate the relations would have a mass approaching even 1% of our estimated mass for T. rex. Of our estimates, the sustainable travel speed of 0.42 m s ‾ 1 seems rather low for a bipedal animal with 2.5 m legs (see Fitzgerald (2002) and references therein). If we repeat our calculations assuming a sustainable running speed of 2.1 m s ‾ 1, then this changes equation (2.7) to 1600 f E m in =. d (2.8) The faster running speed increases the area that can be swept for food faster than it increases the total energetic requirements of that animal, and so this leads to a reduction in the food density required to sustain the scavenger. Thus, our initial assumption of a low running speed can be seen as conservative, making a scavenging lifestyle challenging to maintain. Some scientists consider that mammals (rather than reptiles) are a more appropriate model for dinosaurs (e.g. Bakker 2001). It is possible to repeat our calculations under such an assumption. Schmidt-Nielson (1984) suggests that this would change our equation for R to R = 0.38 M 0.83, (2.9) increasing R substantially to 2300 W for our 6000 kg animal. Calder (1996) suggests that, for a mammal, the equation for S becomes S = 10.7 vM 0.68. (2.10) Bennett & Ruben (1979) suggest that the sustainable speed of mammals is 50% of their maximum speed, hence we will assume that v is 2.1 m s ‾1. If we finally assume that a is unchanged at 0.5, then (using mammals rather than reptiles as a model) changes equation (2.7) to 3100 f E m in =. d (2.11) Hence, we see that substantial compensation for higher resting and movement costs in a mammal-like T. rex may come from a mammalian physiology allowing a higher sustainable rate of movement. The consequence of this is that the minimum food density required by our scavenger is only slightly increased if a mammalian model rather than a reptilian model is assumed. 3. CONCLUSIONS Our calculation suggests that T. rex would be able to gather enough food to survive as a pure scavenger if a number of conditions are met. One is that the ecosystem yields the same density of carrion as the current Serengeti. Estimates of primary productivity at the place and time appropriate to T. rex vary widely but encompass values similar to that of the present-day Serengeti (Beerling & Woodward 2001). Any given primary productivity would have supported a greater biomass of ectothermic dinosaurs compared to the endothermic mammals that dominate the extant Serengeti (Farlow 1990). This higher biomass will more than compensate for the lower turnover rate per unit biomass that one would predict if dinosaurian herbivores had longer lifespans than the mammalian herbivores of the extant Serengeti, on account both of their larger size and probably lower specific metabolic rates. Another condition is that T. rex can detect carcasses at a distance of 80 m. Given the performance of polar bears in detecting seals over distances of kilometres (Stirling 1977) and the ability of turkey vultures to find 80% of experimentally provided chicken carcasses in tropical rainforest within 12 hours of presentation (Houston 1986), this seems likely to have been comfortably within T. rex ’s compass. Brochu (2000) argues, on the basis of computed tomographic analysis of a fossil skull, that T. rex had greatly enlarged olfactory bulbs, suggestive of high olfactory acuity. Farlow (1994) suggests that the upright stance of T. rex could have aided carrion location, both by visual and olfactory pathways. We also assumed that the fallen carcass was only detectable to T. rex for a period of 24 hours. Little is known about how long a carcass is accessible to vertebrate scavenges. Small (chicken) carcasses in tropical African forests were totally consumed by maggots within 3 days (Houston 1987). Hence, our assumption that prey is only available for 1 day seems entirely reasonable, and if anything on the low side. Our final assumption that our focal T. rex individual is able to find all the carcasses that fall in areas where it searches seems less plausible. It is likely that our T. rex would experience competition from other species and from other members of its own species. However, if we arbitrarily assume that our focal individual is only able to access 25% of the carcasses that fall, so that the ecosystem has effectively only 25% of the carrion density of the Serengeti (7.75 J m ‾2), then (from figure 1) we see that T. rex would have to be able to detect prey at a distance of 330 m to balance its energy budget. This is more challenging, but still seems within the bounds of the possible, especially if, like many extant reptiles (Zug et al. 2001), T. rex had an effective sense of smell. Hence, our conclusion is that an energy budget analysis suggests that a reptile as large as T. rex could have survived using a purely scavenging lifestyle, providing that competition for carrion was low. This conclusion leads to the obvious question, why is there not a T. rex- like scavenger on the Serengeti today? Or generally, we must ask why vultures are the only extant vertebrates that have a predominantly scavenging lifestyle. The answer may be that an avian scavenger can outcompete a terrestrial one because, as mentioned in § 1, the key requirement for a scavenger is to minimize energy expenditure while searching. Compared to terrestrial locomotion, even powered flying is faster and much less energetically expensive per distance covered (Schmidt- Nielson 1984), and birds like vultures that make extensive use of soaring have dramatically lower energy expenditure than any terrestrial scavenger could have. If T. rex was a scavenger, then this was probably only possible because avian radiation had yet to have a substantial effect on ecosystems. It may well be, as suggested by Farlow (1994), that T. rex was an opportunist flesh eater, combining scavenging carrion with active predation. That said, our calculations suggest that total (or near total) dependence on carrion (in the manner of extant vultures) may at least have been feasible.Published as part of Ruxton, Graeme D. & Hou
El cambio social
No full textThe concept of social change refers to alterations and modifications in the social behavior and the cultural values of determinated social systems and structures. In opposition to the so called social progress, social change has no teologic meaning. Social system means a structure of social processes and relations showing some regularity. The dichotomy between social statics (structures) and social dynamics (change) is therefore incorrect, because the first does not exist in reality. Cultural changes are but functions of the social changes. Among the functions which are contributions of a social system to the fundamental needs of its members to a more inclusive social system, the author distinguishes actual functions, latent or not evident functions and disfunctions (of negative effect).
With regard to causation, the author points out MAV IVER's classification into distributive, collective and conjunctural phenomena. To forecast and control socio-cultural phenomena, a scientific methods is necessary. After pointing out the conditions for a correct scientific methodology, the author explains the modern complementary and qualitative trends: typology, the same combined with psychology and cultural anthropology and the "functional process", which reduces social change to a manageable analytical process. Finally, he examines five basic aspects of the social change process: social deviations, innovations, the innovation valuating process the transition phase and the institutionalization processInstituto de Investigaciones Económica
El cambio social
No full textThe concept of social change refers to alterations and modifications in the social behavior and the cultural values of determinated social systems and structures. In opposition to the so called social progress, social change has no teologic meaning. Social system means a structure of social processes and relations showing some regularity. The dichotomy between social statics (structures) and social dynamics (change) is therefore incorrect, because the first does not exist in reality. Cultural changes are but functions of the social changes. Among the functions which are contributions of a social system to the fundamental needs of its members to a more inclusive social system, the author distinguishes actual functions, latent or not evident functions and disfunctions (of negative effect). With regard to causation, the author points out MAV IVER's classification into distributive, collective and conjunctural phenomena. To forecast and control socio-cultural phenomena, a scientific methods is necessary. After pointing out the conditions for a correct scientific methodology, the author explains the modern complementary and qualitative trends: typology, the same combined with psychology and cultural anthropology and the "functional process", which reduces social change to a manageable analytical process. Finally, he examines five basic aspects of the social change process: social deviations, innovations, the innovation valuating process the transition phase and the institutionalization proces
A MODIFIED CASE STUDY EXAMINING THE EFFECTS OF SPECIFIC SCHOOL GRADE-LEVEL ORGANIZATIONAL MODELS ON NINTH-GRADE LEARNERS
No full textThis doctoral dissertation represents a qualitative study employing a modified case study research design that is intended to assess the perspectives of school practitioners (i.e., principals, guidance counselors, and teachers) who work with ninth graders relevant to their perceptions of the developmental needs of those students, how their respective schools address those needs, and the effects their schools’ grade-level organizational plans may have on grade nine. This study employs semi-structured interviews, document reviews, and direct observations for data collection. Two case sites were selected for this dissertation—one populated by students in grades nine through twelve (9-12) and another with pupils in grades seven through nine (7-9). Both sites were selected purposefully on the basis of their grade-level configurations, their contemporary and historical relevance to ninth-grade-level education, and their proximity to the principal researcher. Sample groups at each school included 10 practitioners who worked directly with ninth graders within a multitude of professional realms, particularly administration, counseling, and teaching. Upon site selection, building principals were recruited for participation in this study; henceforth, those subjects selected nine other participants of faculty rank based on their professional positions and affiliations with students at the ninth-grade level.
The data seems to indicate that practitioners at the grades 9-12 high school perceive ninth graders differently from that of their counterparts at the grades 7-9 junior high school. The high-school subjects generally describe ninth graders as being immature, whereas participants at the junior high school perceive them the opposite of that. It also appears that participants at the grades 9-12 site lack consensus on the attributes of ninth-grade developmental needs with some questioning the appropriateness and/or legitimacy of four-year high schools for educating students at that grade level, while others ardently support that construct. Conversely, practitioners at the grades 7-9 junior high school seem to be unified in their perspectives on ninth-grade-level development—contending that ninth graders are better educated in junior high schools versus senior high schools and that their school is developmentally appropriate and more suitable for ninth-grade learners
β-diversity of deep-sea holothurians and asteroids along a bathymetric gradient (NE Atlantic)
No full textMeasuring and understanding patterns of ?-diversity remain major challenges in community ecology. Recently, ?-diversity has been shown to consist of 2 distinct components: (1) spatial turnover and (2) species loss leading to nestedness. Both components structure deep-sea macrofaunal assemblages but vary in importance among taxa and ocean basins and with energy availability. Here, we present the first evidence for turnover and nestedness along a bathymetric gradient in 2 major megafaunal taxa, holothurians and asteroids. Turnover is the dominant component of ?-diversity throughout bathyal and abyssal zones in both taxa, despite major differences in ?-diversity and trophic composition. High spatial turnover suggests a role for evolutionary adaptation to environmental circumstances within depth bands. This pattern differs fundamentally from those in some macrofaunal groups in low-energy environments where abyssal nestedness is high and diversity low, with diversity maintained partly by source-sink dynamics
Examination of 2,4-D tolerance in perennial Glycine species and the involvement of cytochrome P-450 as a tolerance mechanism
No full textHigh levels of tolerance to 2,4-D ((2,4-dichlorophenoxy)acetic acid) were expressed at the cell and whole plant level by several accessions of wild perennial Glycine species. Heterotrophic cell suspension cultures of soybean (Glycine max (L.) Merr.) and four perennial Glycine accessions were used to investigate (\sp{14}C) 2,4-D uptake and metabolism. Uptake of 2,4-D was similar between soybean and the perennials. However, soybean metabolized almost 60% less 2,4-D than the perennials at an equivalent 2,4-D concentration. The primary metabolite produced by the tolerant perennial accessions was the glycoside conjugate of 4-OH-2,5-D. Soybean and less tolerant perennials lines generated primarily amino acid conjugates of 2,4-D.The P-450 inhibitor tetcyclasis significantly reduced 2,4-D tolerance of the perennial Glycine tabacina accession IL344 by inhibiting 2,4-D metabolism 60% and formation of the hydroxylated metabolites by 80%. Tetcyclasis had no effect on soybean tolerance or 2,4-D metabolism. IL344 had 3-times more cytochrome P-450 protein (60 pmol/mg microsomal protein) than soybean and expressed one constitutive 46 kD microsomal P-450 polypeptide that strongly cross-reacted to antisera raised to avocado P-450. Soybean had a single inducible (by 2,4-D treatment) P-450 polypeptide of similar molecular weight. Ultrastructural observations were made using transmission electron microscopy and revealed that IL344 had a large distribution of smooth endoplasmic reticulum as well as convoluted nuclear membrane. Both represent indirect ultrastructural evidence for the localization of cytochrome P-450, which was verified using immunocytochemistry (immunogold labelling). In contrast, rough endoplasmic reticulum predominated in soybean.Made available in DSpace on 2011-05-07T13:56:58Z (GMT). No. of bitstreams: 2
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Src Family Tyrosine Kinase Signaling in Mouse and Human Embryonic Stem Cells
No full textEmbryonic stem (ES) cells are derived from the inner cell mass of the blastocyst stage embryo and are characterized by self-renewal and pluripotency. Previous work has implicated the Src family of protein-tyrosine kinases (SFKs) in the self-renewal and differentiation of mouse ES (mES) cells. These kinases display dynamic expression and activity changes during ES cell differentiation, suggesting distinct functions in the control of developmental fate. To test the hypothesis that c-Src and its closest phylogenetic relative, c-Yes, act in biological opposition to one another, I first showed that enforced expression of active c-Yes blocked ES cell differentiation to embryoid bodies by maintaining pluripotency gene expression. To determine the interplay of c-Src and c-Yes in mES cell fate determination, I employed a chemical genetics approach to generate c-Src and c-Yes mutants that are resistant to A-419259, a potent pyrrolopyrimidine inhibitor of the Src kinase family. This method allowed us to investigate individual kinase function in the presence of A-419259. I found that c-Src activity alone induces mES cell differentiation to the ectoderm and endoderm, while c-Yes inhibits this process. These studies show that even closely related kinases such as c-Src and c-Yes have unique and opposing functions in the same cell type.
While Src kinase signaling has been investigated in mES cells, the role of this kinase family in human ES (hES) cells is largely unknown. Using quantitative real-time RT-PCR, I determined the relative expression profile of individual SFK members in undifferentiated hES cells vs. embryoid bodies derived from them. Like mES cells, hES cells express multiple SFK members with dynamic transcription changes during EB differentiation, indicating that individual members may play non-redundant roles. To assess the role of SFK activity in hES cells, I treated hES cell cultures with SFK inhibitors. SFK inhibition maintained hES cell colony morphology and expression of the pluripotency marker Tra-1-60 in differentiation medium. These observations support a role for Src family kinase signaling in the regulation of hES fate, and suggest that some parallels may exist in mouse and human ES cells for this intracellular signaling network
Rare event searches based on micromegas detectors: The T-REX project
No full textYıldız, Süleyman Cenk (Dogus Author) -- The conference paper was firstly submitted to 12th International Conference on Topics in Astroparticle and Underground Physics.Micromegas readouts are an attractive option for many of the rare event searches, due to their performance regarding energy resolution, gain stability, homogeneity and material budget. The T-REX project aims at developing further these novel readout techniques for Time Projection Chambers and their potential use in experiments searching for rare events. Here we will refer to the latest results regarding the use and prospects of Micromegas read-outs in axion physics (CAST and the future helioscope), as well as the R&D carried out within NEXT, to search for the neutrinoless double-beta decay
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