C. Neal Stewart
- Published in print:
- 2004
- Published Online:
- September 2007
- ISBN:
- 9780195157451
- eISBN:
- 9780199790388
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195157451.001.0001
- Subject:
- Biology, Biotechnology
From years prior to the release of the first commercial transgenic crop in 1995 to the present, many concerned activists, regulators, and scientists have questioned how genetic engineering might ...
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From years prior to the release of the first commercial transgenic crop in 1995 to the present, many concerned activists, regulators, and scientists have questioned how genetic engineering might impact the environment. No measurable negative environmental impacts have been observed for commercial genetically modified crops to date, even though several risks have been identified in experimental releases. Even so, none have approached doomsday scenarios posed by activists. The risks that have been extensively studied are gene flow from crops to weeds or crop landraces; side-effects of insecticidal transgenic proteins, such as accidental killing of monarch butterflies or beneficial insects; viral recombination; and transgene combinations. Close examination has uncovered no negative effects, but plenty of positive environmental impacts from growing crops engineered for insect resistance and herbicide resistance. Insect resistant cotton and corn kill only the insects that attempt to eat the crops and have saved several million gallons of chemical insecticide applications. Herbicide resistant soybean and corn have helped in soil conservation efforts since farmers do not have to use as much tillage to control weeds. In addition to these benefits, scientists are conducting research to produce genetically engineered plants to clean up toxins, produce plastics and biofuels, and perform other ecological services. The responsible use of genetic engineering is part of sustainable agriculture now and in the future.Less
From years prior to the release of the first commercial transgenic crop in 1995 to the present, many concerned activists, regulators, and scientists have questioned how genetic engineering might impact the environment. No measurable negative environmental impacts have been observed for commercial genetically modified crops to date, even though several risks have been identified in experimental releases. Even so, none have approached doomsday scenarios posed by activists. The risks that have been extensively studied are gene flow from crops to weeds or crop landraces; side-effects of insecticidal transgenic proteins, such as accidental killing of monarch butterflies or beneficial insects; viral recombination; and transgene combinations. Close examination has uncovered no negative effects, but plenty of positive environmental impacts from growing crops engineered for insect resistance and herbicide resistance. Insect resistant cotton and corn kill only the insects that attempt to eat the crops and have saved several million gallons of chemical insecticide applications. Herbicide resistant soybean and corn have helped in soil conservation efforts since farmers do not have to use as much tillage to control weeds. In addition to these benefits, scientists are conducting research to produce genetically engineered plants to clean up toxins, produce plastics and biofuels, and perform other ecological services. The responsible use of genetic engineering is part of sustainable agriculture now and in the future.
Arndt Sorge
- Published in print:
- 2005
- Published Online:
- September 2007
- ISBN:
- 9780199278909
- eISBN:
- 9780191706820
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199278909.003.0004
- Subject:
- Business and Management, International Business
Recombinations of liberal and corporatist economic institutions, of hierarchical subordination and lateral association have marked German socio-economic history from the beginnings of modernity until ...
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Recombinations of liberal and corporatist economic institutions, of hierarchical subordination and lateral association have marked German socio-economic history from the beginnings of modernity until today. These have been associated with recombinations of internationalization and provincialization. But such opposed tendencies and characteristics have also prevailed in different historical periods. Whereas the first half of the 19th century, its end, and the post-WW II period were marked by economic liberalization, other periods were marked by economic corporatism, notably during the totalitarian period of the 3rd Reich. Recombinations and shifts, one way or the other, have been influenced by national catastrophes and the direction that their political aftermath took.Less
Recombinations of liberal and corporatist economic institutions, of hierarchical subordination and lateral association have marked German socio-economic history from the beginnings of modernity until today. These have been associated with recombinations of internationalization and provincialization. But such opposed tendencies and characteristics have also prevailed in different historical periods. Whereas the first half of the 19th century, its end, and the post-WW II period were marked by economic liberalization, other periods were marked by economic corporatism, notably during the totalitarian period of the 3rd Reich. Recombinations and shifts, one way or the other, have been influenced by national catastrophes and the direction that their political aftermath took.
Arndt Sorge
- Published in print:
- 2005
- Published Online:
- September 2007
- ISBN:
- 9780199278909
- eISBN:
- 9780191706820
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199278909.003.0007
- Subject:
- Business and Management, International Business
This last chapter sums up the basic message and draws some conclusions. Rather than opposing convergence and divergence, how supranational convergence breeds new local divergence should be explained. ...
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This last chapter sums up the basic message and draws some conclusions. Rather than opposing convergence and divergence, how supranational convergence breeds new local divergence should be explained. The impact of international developments is always mediated by local institutions and culture, and the latter may become more distinctive through the former. Previous processes of internationalization set the scene for the local fashioning of more recent processes. Recombination is the rule, and any national ‘model’ of any time is the result of earlier recombinations of opposed tendencies. The institutions associated with the South Germanic bedrock and coordinated market economies, specifically, are viable by recombination, as institutions invariably are. They should not be blamed for the handling of German unification — a unique phenomenon in the world — handled with a mixture of heroism and blunders, the latter mainly with respect to the distribution of the social security and employment policy financial burden.Less
This last chapter sums up the basic message and draws some conclusions. Rather than opposing convergence and divergence, how supranational convergence breeds new local divergence should be explained. The impact of international developments is always mediated by local institutions and culture, and the latter may become more distinctive through the former. Previous processes of internationalization set the scene for the local fashioning of more recent processes. Recombination is the rule, and any national ‘model’ of any time is the result of earlier recombinations of opposed tendencies. The institutions associated with the South Germanic bedrock and coordinated market economies, specifically, are viable by recombination, as institutions invariably are. They should not be blamed for the handling of German unification — a unique phenomenon in the world — handled with a mixture of heroism and blunders, the latter mainly with respect to the distribution of the social security and employment policy financial burden.
Takashi Fujimoto
- Published in print:
- 2004
- Published Online:
- September 2007
- ISBN:
- 9780198530282
- eISBN:
- 9780191713149
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198530282.003.0003
- Subject:
- Physics, Nuclear and Plasma Physics
This chapter presents an overview of atomic processes which play important roles in plasma spectroscopy. Starting with the atomic wavefunction of hydrogen, the absorption oscillator strengths between ...
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This chapter presents an overview of atomic processes which play important roles in plasma spectroscopy. Starting with the atomic wavefunction of hydrogen, the absorption oscillator strengths between discrete levels and their continuation to the continuum states (i.e., the photoionization cross section) are derived. The spontaneous transition probability and the radiative recombination rate coefficient follow. Excitation cross section by electron impact is discussed somewhat in detail. Several general features of cross sections are noted (e.g., the Bethe limit at high energy, different behaviours near the excitation threshold between neutral atoms and ions, and the resonance structure for ions). Continuation from the excitation cross section to the ionization cross section is noted. Three-body recombination, autoionization, dielectronic recombination, and satellite lines are also introduced.Less
This chapter presents an overview of atomic processes which play important roles in plasma spectroscopy. Starting with the atomic wavefunction of hydrogen, the absorption oscillator strengths between discrete levels and their continuation to the continuum states (i.e., the photoionization cross section) are derived. The spontaneous transition probability and the radiative recombination rate coefficient follow. Excitation cross section by electron impact is discussed somewhat in detail. Several general features of cross sections are noted (e.g., the Bethe limit at high energy, different behaviours near the excitation threshold between neutral atoms and ions, and the resonance structure for ions). Continuation from the excitation cross section to the ionization cross section is noted. Three-body recombination, autoionization, dielectronic recombination, and satellite lines are also introduced.
John C. Avise
- Published in print:
- 2008
- Published Online:
- January 2009
- ISBN:
- 9780195369670
- eISBN:
- 9780199871063
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195369670.003.0001
- Subject:
- Biology, Evolutionary Biology / Genetics
Although clonality is often discussed in reference to whole organisms, the phenomenon also applies to (and is underlain by) genetic processes operating within each individual. All forms of clonal ...
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Although clonality is often discussed in reference to whole organisms, the phenomenon also applies to (and is underlain by) genetic processes operating within each individual. All forms of clonal reproduction begin with the faithful replication of genetic material. This chapter discusses the clonal propagation of nucleic acids (via DNA replication) and of entire nuclear genomes and chromosome sets (via mitosis) in populations of somatic cells. It also describes how mitochondrial genomes, as well as particular kinds of sex chromosomes, provide special examples of genetic systems that abstain from recombination. The net result of such micro-asexual processes is a multicellular individual, which can thus be viewed as a tightly knit colony of clonemate cells.Less
Although clonality is often discussed in reference to whole organisms, the phenomenon also applies to (and is underlain by) genetic processes operating within each individual. All forms of clonal reproduction begin with the faithful replication of genetic material. This chapter discusses the clonal propagation of nucleic acids (via DNA replication) and of entire nuclear genomes and chromosome sets (via mitosis) in populations of somatic cells. It also describes how mitochondrial genomes, as well as particular kinds of sex chromosomes, provide special examples of genetic systems that abstain from recombination. The net result of such micro-asexual processes is a multicellular individual, which can thus be viewed as a tightly knit colony of clonemate cells.
John C. Avise
- Published in print:
- 2008
- Published Online:
- January 2009
- ISBN:
- 9780195369670
- eISBN:
- 9780199871063
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195369670.003.0002
- Subject:
- Biology, Evolutionary Biology / Genetics
Sexual reproduction is the antithesis of clonality because genes that are faithfully copied during asexual replication are genetically scrambled (recombined) during the sexual processes of meiosis ...
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Sexual reproduction is the antithesis of clonality because genes that are faithfully copied during asexual replication are genetically scrambled (recombined) during the sexual processes of meiosis and fertilization. Sex has long been an evolutionary enigma because it appears at face value to entail several fitness costs and risks in the short term whereas its potential benefits would seem to be rather diffuse and postponed. This chapter reviews the diverse explanations for recombinational sex, ranging from the level of molecular genetics to the echelons of short-term ecology and long-term evolution. It thus sets the stage for the book's extended thesis that any attempt to understand the adaptive significance of sex is likely to be facilitated by analyzing clonal systems, and vice versa.Less
Sexual reproduction is the antithesis of clonality because genes that are faithfully copied during asexual replication are genetically scrambled (recombined) during the sexual processes of meiosis and fertilization. Sex has long been an evolutionary enigma because it appears at face value to entail several fitness costs and risks in the short term whereas its potential benefits would seem to be rather diffuse and postponed. This chapter reviews the diverse explanations for recombinational sex, ranging from the level of molecular genetics to the echelons of short-term ecology and long-term evolution. It thus sets the stage for the book's extended thesis that any attempt to understand the adaptive significance of sex is likely to be facilitated by analyzing clonal systems, and vice versa.
Graham Bell
- Published in print:
- 2007
- Published Online:
- May 2008
- ISBN:
- 9780198569725
- eISBN:
- 9780191717741
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198569725.003.0004
- Subject:
- Biology, Evolutionary Biology / Genetics
The evolution of asexual organisms in laboratory microcosms is constrained by the lack of genetic exchange and by isolation from the rest of the world. When these constraints are relaxed, the rate of ...
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The evolution of asexual organisms in laboratory microcosms is constrained by the lack of genetic exchange and by isolation from the rest of the world. When these constraints are relaxed, the rate of adaptation and how it is acquired may change. The first section in this chapter is called Horizontal transmission and details gene transfer agents; gene cassettes; and conjugative plasmids. The second section is entitled Sex and it explains all about dominance; sorting in asexual diploid populations; sorting in sexual diplonts; heterozygotes; recombination; the limits to adaptation; purifying selection in sexual populations: mutation clearance; synthetic lethal mutations; mean fitness under purifying selection; directional selection in sexual populations: mutation assembly; directional selection in sexual populations: mutation liberation; the effect of recombination in phage; the effect of sex in microbes; the effect of recombination in Drosophila; and finally sex and the response to selection. The third section is about dispersal and informs on population structure; subdivided asexual populations; subdivided sexual diploid populations; the shifting balance.Less
The evolution of asexual organisms in laboratory microcosms is constrained by the lack of genetic exchange and by isolation from the rest of the world. When these constraints are relaxed, the rate of adaptation and how it is acquired may change. The first section in this chapter is called Horizontal transmission and details gene transfer agents; gene cassettes; and conjugative plasmids. The second section is entitled Sex and it explains all about dominance; sorting in asexual diploid populations; sorting in sexual diplonts; heterozygotes; recombination; the limits to adaptation; purifying selection in sexual populations: mutation clearance; synthetic lethal mutations; mean fitness under purifying selection; directional selection in sexual populations: mutation assembly; directional selection in sexual populations: mutation liberation; the effect of recombination in phage; the effect of sex in microbes; the effect of recombination in Drosophila; and finally sex and the response to selection. The third section is about dispersal and informs on population structure; subdivided asexual populations; subdivided sexual diploid populations; the shifting balance.
Graham Bell
- Published in print:
- 2007
- Published Online:
- May 2008
- ISBN:
- 9780198569725
- eISBN:
- 9780191717741
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198569725.003.0012
- Subject:
- Biology, Evolutionary Biology / Genetics
There is good but not conclusive evidence that sex is indirectly selected because it facilitates adaptation, and in particular adaptation to coevolving antagonists. Competition for sexual partners ...
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There is good but not conclusive evidence that sex is indirectly selected because it facilitates adaptation, and in particular adaptation to coevolving antagonists. Competition for sexual partners leads to characteristic male and female adaptations inconsistent with natural selection. This chapter starts with a section called Evolution of sex and it discusses Calkins' experiment; Muller's Ratchet; artificial selection for recombination; sex and the rate of adaptation; the correlated response to directional selection; the Red Queen; and sib competition. The final subsection is called Somewhat sexual. The second section is called The alternation of generations and is about antagonism of sexual selection and natural selection; vegetative theories of the life cycle; the sexual theory of the life cycle; and sporophyte and gametophyte. The third section, Gender, talks firstly about many genders and then discusses male and female and gamete competition. It also details the gender of individuals and parts; equality under Fisher; gender allocation; homothallism; and finally self-fertilization. The final section here is entitled Beauty and the Beast and discusses Bateman's Principle; artificial sexual selection; sexual contests; male x female interaction; sexual choice; sexual ornaments; and finally includes a subsection called battles of the sexes.Less
There is good but not conclusive evidence that sex is indirectly selected because it facilitates adaptation, and in particular adaptation to coevolving antagonists. Competition for sexual partners leads to characteristic male and female adaptations inconsistent with natural selection. This chapter starts with a section called Evolution of sex and it discusses Calkins' experiment; Muller's Ratchet; artificial selection for recombination; sex and the rate of adaptation; the correlated response to directional selection; the Red Queen; and sib competition. The final subsection is called Somewhat sexual. The second section is called The alternation of generations and is about antagonism of sexual selection and natural selection; vegetative theories of the life cycle; the sexual theory of the life cycle; and sporophyte and gametophyte. The third section, Gender, talks firstly about many genders and then discusses male and female and gamete competition. It also details the gender of individuals and parts; equality under Fisher; gender allocation; homothallism; and finally self-fertilization. The final section here is entitled Beauty and the Beast and discusses Bateman's Principle; artificial sexual selection; sexual contests; male x female interaction; sexual choice; sexual ornaments; and finally includes a subsection called battles of the sexes.
C. Neal Stewart
- Published in print:
- 2004
- Published Online:
- September 2007
- ISBN:
- 9780195157451
- eISBN:
- 9780199790388
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195157451.003.0009
- Subject:
- Biology, Biotechnology
One success story in plant biotechnology is the production of virus-resistant papaya, which saved the papaya industry in Hawaii. The virus-resistant plants contain a piece of viral DNA that protects ...
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One success story in plant biotechnology is the production of virus-resistant papaya, which saved the papaya industry in Hawaii. The virus-resistant plants contain a piece of viral DNA that protects against ring-spot virus. However, people have worried that wild virus sequence might interact and recombine with virus-derived transgenes, with the worst-case scenario being the creation of new and more virulent viruses. A forced exchange of sequence has been produced in lab settings under artificial selection conditions, but viral recombination with transgenes have never been observed in the field. In addition, several prevalent conditions do not favor viral recombination of this sort. The biggest reasons are that the transgenic sequence adds no novel information into the system, and the virus-resistant plants decrease viral load in the plant, which decreases opportunity for recombination.Less
One success story in plant biotechnology is the production of virus-resistant papaya, which saved the papaya industry in Hawaii. The virus-resistant plants contain a piece of viral DNA that protects against ring-spot virus. However, people have worried that wild virus sequence might interact and recombine with virus-derived transgenes, with the worst-case scenario being the creation of new and more virulent viruses. A forced exchange of sequence has been produced in lab settings under artificial selection conditions, but viral recombination with transgenes have never been observed in the field. In addition, several prevalent conditions do not favor viral recombination of this sort. The biggest reasons are that the transgenic sequence adds no novel information into the system, and the virus-resistant plants decrease viral load in the plant, which decreases opportunity for recombination.
Takashi Fujimoto
- Published in print:
- 2004
- Published Online:
- September 2007
- ISBN:
- 9780198530282
- eISBN:
- 9780191713149
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198530282.003.0005
- Subject:
- Physics, Nuclear and Plasma Physics
The effective rates for ionization and for recombination including processes via excited levels are expressed as the collisional-radiative (CR) ionization rate coefficient and the CR recombination ...
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The effective rates for ionization and for recombination including processes via excited levels are expressed as the collisional-radiative (CR) ionization rate coefficient and the CR recombination rate coefficient, respectively. Ionization-balance plasma is defined from these CR rate coefficients. For excited-level populations, the contribution from the ionizing plasma component and that from the recombining plasma component can be comparable in magnitude, and the emission line intensity takes the maximum at about the optimum temperature at which the ionization ratio is 1. The ionizing plasma is defined as those which have much lower ionization ratio than that for ionization balance, so that the ionizing plasma component will be dominant in the populations, and vice versa for the recombining plasma. The excited-level population is proportional to the ionization flux, or to the recombination flux. Thus, an ionizing plasma or a recombining plasma produces strong line emissions, while an ionization-balance plasma emits less intense lines.Less
The effective rates for ionization and for recombination including processes via excited levels are expressed as the collisional-radiative (CR) ionization rate coefficient and the CR recombination rate coefficient, respectively. Ionization-balance plasma is defined from these CR rate coefficients. For excited-level populations, the contribution from the ionizing plasma component and that from the recombining plasma component can be comparable in magnitude, and the emission line intensity takes the maximum at about the optimum temperature at which the ionization ratio is 1. The ionizing plasma is defined as those which have much lower ionization ratio than that for ionization balance, so that the ionizing plasma component will be dominant in the populations, and vice versa for the recombining plasma. The excited-level population is proportional to the ionization flux, or to the recombination flux. Thus, an ionizing plasma or a recombining plasma produces strong line emissions, while an ionization-balance plasma emits less intense lines.
Norman A. Johnson
- Published in print:
- 2007
- Published Online:
- September 2007
- ISBN:
- 9780195306750
- eISBN:
- 9780199790203
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195306750.003.0006
- Subject:
- Biology, Evolutionary Biology / Genetics
Unlike most of our genes, mitochondrial DNA is transmitted solely by mothers; males are a dead-end for the mitochondria. Evolutionary biologists have determined that the most recent common ancestor ...
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Unlike most of our genes, mitochondrial DNA is transmitted solely by mothers; males are a dead-end for the mitochondria. Evolutionary biologists have determined that the most recent common ancestor of all mitochondrial genetic variants was a woman who lived in Africa about 200,000 years ago. That we can trace back all mitochondrial DNA back to a single female (the mitochondrial Eve) is not a surprise. In fact, it is a simple consequence of population genetics. The location in time and place of this common ancestor does inform us about human demography and evolution. However, genetic recombination coupled with evolutionary forces will cause different genes to vary in their evolutionary histories. The mitochondrial “Eve” did not know the common ancestor of Y chromosomes, “Adam”. In fact, it is likely that the Y-chromosome Adam lived tens of thousands of years after the mitochondrial Eve.Less
Unlike most of our genes, mitochondrial DNA is transmitted solely by mothers; males are a dead-end for the mitochondria. Evolutionary biologists have determined that the most recent common ancestor of all mitochondrial genetic variants was a woman who lived in Africa about 200,000 years ago. That we can trace back all mitochondrial DNA back to a single female (the mitochondrial Eve) is not a surprise. In fact, it is a simple consequence of population genetics. The location in time and place of this common ancestor does inform us about human demography and evolution. However, genetic recombination coupled with evolutionary forces will cause different genes to vary in their evolutionary histories. The mitochondrial “Eve” did not know the common ancestor of Y chromosomes, “Adam”. In fact, it is likely that the Y-chromosome Adam lived tens of thousands of years after the mitochondrial Eve.
Julian C. Knight
- Published in print:
- 2009
- Published Online:
- September 2009
- ISBN:
- 9780199227693
- eISBN:
- 9780191711015
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199227693.003.0009
- Subject:
- Biology, Evolutionary Biology / Genetics, Disease Ecology / Epidemiology
The extent of single nucleotide polymorphism is reviewed, together with insights gained into the nature of allelic architecture in terms of haplotypes, linkage disequilibrium and recombination. The ...
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The extent of single nucleotide polymorphism is reviewed, together with insights gained into the nature of allelic architecture in terms of haplotypes, linkage disequilibrium and recombination. The utility of SNPs in defining genetic determinants of common disease is discussed including the rationale, results and diverse applications of the International HapMap Project. The recent development and application of genome-wide association studies is reviewed including the Wellcome Trust Case Control Consortium study of seven common diseases. Issues relating to design, analysis and interpretation of such studies are described. A detailed review of age-related macular degeneration and inflammatory bowel disease is presented, two common multifactorial diseases where genome-wide association studies have recently enjoyed considerable success. Research in these diseases illustrates the timeline of different approaches used in defining genetic determinants of common disease and how such analyses can provide novel insights into disease pathogenesis.Less
The extent of single nucleotide polymorphism is reviewed, together with insights gained into the nature of allelic architecture in terms of haplotypes, linkage disequilibrium and recombination. The utility of SNPs in defining genetic determinants of common disease is discussed including the rationale, results and diverse applications of the International HapMap Project. The recent development and application of genome-wide association studies is reviewed including the Wellcome Trust Case Control Consortium study of seven common diseases. Issues relating to design, analysis and interpretation of such studies are described. A detailed review of age-related macular degeneration and inflammatory bowel disease is presented, two common multifactorial diseases where genome-wide association studies have recently enjoyed considerable success. Research in these diseases illustrates the timeline of different approaches used in defining genetic determinants of common disease and how such analyses can provide novel insights into disease pathogenesis.
P. K. Basu
- Published in print:
- 2003
- Published Online:
- January 2010
- ISBN:
- 9780198526209
- eISBN:
- 9780191706790
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198526209.003.0010
- Subject:
- Physics, Atomic, Laser, and Optical Physics
This chapter discusses various radiative recombination processes in a semiconductor, the rates of the processes, and the nature of the emission spectra. Band-to-band, band-to-impurity, and excitonic ...
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This chapter discusses various radiative recombination processes in a semiconductor, the rates of the processes, and the nature of the emission spectra. Band-to-band, band-to-impurity, and excitonic processes are considered. Excess carriers are characterized by a lifetime and the relationship between lifetime and recombination rate is developed. A connection exists between absorption and emission rates. This relationship is established, and in some cases, the absorption spectra and the relationship established are used to predict emission spectra. The processes in both direct and indirect band materials are covered. Exercises are provided at the end of the chapter.Less
This chapter discusses various radiative recombination processes in a semiconductor, the rates of the processes, and the nature of the emission spectra. Band-to-band, band-to-impurity, and excitonic processes are considered. Excess carriers are characterized by a lifetime and the relationship between lifetime and recombination rate is developed. A connection exists between absorption and emission rates. This relationship is established, and in some cases, the absorption spectra and the relationship established are used to predict emission spectra. The processes in both direct and indirect band materials are covered. Exercises are provided at the end of the chapter.
Ivan Pelant and Jan Valenta
- Published in print:
- 2012
- Published Online:
- May 2012
- ISBN:
- 9780199588336
- eISBN:
- 9780191738548
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199588336.003.0006
- Subject:
- Physics, Atomic, Laser, and Optical Physics
Nonradiative recombination involves various kinds of transformation of the electronic excitation energy into other types of energy than light. Instead of being emitted as luminescence, there are ...
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Nonradiative recombination involves various kinds of transformation of the electronic excitation energy into other types of energy than light. Instead of being emitted as luminescence, there are three basic ways how the excitation energy can be nonradiatively dissipated: (i) transformation into heat, which comprises multiphonon nonradiative recombination, surface recombination and Auger recombination, (ii) creation of lattice defects and (iii) photochemical changes of the electronically excited material. Relevant kinetic equations are outlined. Criteria conditioning the occurrence of particular processes are discussed. A noteworthy case of the competition between photochemical sensitivity and photoluminescence efficiency in silver halides as a function of temperature is addressed.Less
Nonradiative recombination involves various kinds of transformation of the electronic excitation energy into other types of energy than light. Instead of being emitted as luminescence, there are three basic ways how the excitation energy can be nonradiatively dissipated: (i) transformation into heat, which comprises multiphonon nonradiative recombination, surface recombination and Auger recombination, (ii) creation of lattice defects and (iii) photochemical changes of the electronically excited material. Relevant kinetic equations are outlined. Criteria conditioning the occurrence of particular processes are discussed. A noteworthy case of the competition between photochemical sensitivity and photoluminescence efficiency in silver halides as a function of temperature is addressed.
Aaron L. Berkowitz
- Published in print:
- 2010
- Published Online:
- September 2010
- ISBN:
- 9780199590957
- eISBN:
- 9780191594595
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199590957.003.0003
- Subject:
- Psychology, Cognitive Psychology, Music Psychology
This chapter discusses the pedagogical strategies of the improvisation treatises introduced in the previous chapter. These strategies include transposition, variation, recombination, and the use of ...
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This chapter discusses the pedagogical strategies of the improvisation treatises introduced in the previous chapter. These strategies include transposition, variation, recombination, and the use of models. Comparisons are made between these teaching techniques and those utilized in the pedagogy of improvisation in a wide variety of musical cultures. Drawing on concepts and research from cognitive psychology, the chapter explores how each pedagogical approach could lead to the creation and development of a knowledge base fit for use in the spontaneous generation of idiomatic music in the moment of performance. Transposition is discussed in the context of theories of automatization and proceduralization, variation is explored with reference to work on the cognitive psychology of concepts, and recombination is examined in terms of transitional probabilities and statistical learning.Less
This chapter discusses the pedagogical strategies of the improvisation treatises introduced in the previous chapter. These strategies include transposition, variation, recombination, and the use of models. Comparisons are made between these teaching techniques and those utilized in the pedagogy of improvisation in a wide variety of musical cultures. Drawing on concepts and research from cognitive psychology, the chapter explores how each pedagogical approach could lead to the creation and development of a knowledge base fit for use in the spontaneous generation of idiomatic music in the moment of performance. Transposition is discussed in the context of theories of automatization and proceduralization, variation is explored with reference to work on the cognitive psychology of concepts, and recombination is examined in terms of transitional probabilities and statistical learning.
Takashi Fujimoto
- Published in print:
- 2004
- Published Online:
- September 2007
- ISBN:
- 9780198530282
- eISBN:
- 9780191713149
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198530282.003.0006
- Subject:
- Physics, Nuclear and Plasma Physics
The intensity distribution of the recombination continuum continues smoothly across the ionization limit to the series lines, the upper levels of which are in LTE. Thus, a Boltzmann plot of the ...
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The intensity distribution of the recombination continuum continues smoothly across the ionization limit to the series lines, the upper levels of which are in LTE. Thus, a Boltzmann plot of the excited-level populations is extended to include the continuum-state electrons. Bremsstrahlung, or the free-free continuum radiation, is treated as an extension of the recombination continuum.Less
The intensity distribution of the recombination continuum continues smoothly across the ionization limit to the series lines, the upper levels of which are in LTE. Thus, a Boltzmann plot of the excited-level populations is extended to include the continuum-state electrons. Bremsstrahlung, or the free-free continuum radiation, is treated as an extension of the recombination continuum.
Ivan Pelant and Jan Valenta
- Published in print:
- 2012
- Published Online:
- May 2012
- ISBN:
- 9780199588336
- eISBN:
- 9780191738548
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199588336.003.0009
- Subject:
- Physics, Atomic, Laser, and Optical Physics
Luminescence of disordered (amorphous) semiconductors is due to a different microscopic mechanism compared to those being active in the luminescence of crystalline counterparts with long-range order. ...
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Luminescence of disordered (amorphous) semiconductors is due to a different microscopic mechanism compared to those being active in the luminescence of crystalline counterparts with long-range order. Electron and hole tail states, originating from dangling bonds, play the decisive role. Features typical for the amorphous semiconductor luminescence are discussed, namely: peculiar temperature dependence driven by the demarcation energy and distribution of luminescence decay times. Two theoretical models describing spectral shape of the emission band are examined: the phonon broadening model and the disorder broadening model. Theoretical band shapes are compared with experimental spectra found in amorphous elemental semiconductors. The concept of geminate and non-geminate electron–hole pairs is briefly debated. Multiple nonradiative recombination paths are mentioned as well as luminescence of impurities and defects.Less
Luminescence of disordered (amorphous) semiconductors is due to a different microscopic mechanism compared to those being active in the luminescence of crystalline counterparts with long-range order. Electron and hole tail states, originating from dangling bonds, play the decisive role. Features typical for the amorphous semiconductor luminescence are discussed, namely: peculiar temperature dependence driven by the demarcation energy and distribution of luminescence decay times. Two theoretical models describing spectral shape of the emission band are examined: the phonon broadening model and the disorder broadening model. Theoretical band shapes are compared with experimental spectra found in amorphous elemental semiconductors. The concept of geminate and non-geminate electron–hole pairs is briefly debated. Multiple nonradiative recombination paths are mentioned as well as luminescence of impurities and defects.
Ivan Pelant and Jan Valenta
- Published in print:
- 2012
- Published Online:
- May 2012
- ISBN:
- 9780199588336
- eISBN:
- 9780191738548
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199588336.003.0014
- Subject:
- Physics, Atomic, Laser, and Optical Physics
Stimulated emission and lasing can be achieved easily in a number of semiconductor nanostructures. This chapter gives an overview of a series of physical mechanisms that were found experimentally to ...
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Stimulated emission and lasing can be achieved easily in a number of semiconductor nanostructures. This chapter gives an overview of a series of physical mechanisms that were found experimentally to give rise to positive optical gain in quantum wells, quantum wires and nanocrystals. In quantum wells, these are radiative recombination of localized excitons, LO-phonon assisted exciton recombination and electron–hole plasma luminescence. In quantum wires the data are rather scarce; localized excitons and electron–hole plasma appears to be involved in lasing. Separately treated are the cases of nanocrystals dispersed randomly in a matrix and that of heterostructures with ordered quantum dots (grown by Stranski–Krastanow method). Exciton and biexciton mechanisms of optical gain in quantum dots are analyzed. The crucial competing role of Auger recombination is expressed via the filling factor. Prospects of random lasing in semiconductor nanostructures are outlined.Less
Stimulated emission and lasing can be achieved easily in a number of semiconductor nanostructures. This chapter gives an overview of a series of physical mechanisms that were found experimentally to give rise to positive optical gain in quantum wells, quantum wires and nanocrystals. In quantum wells, these are radiative recombination of localized excitons, LO-phonon assisted exciton recombination and electron–hole plasma luminescence. In quantum wires the data are rather scarce; localized excitons and electron–hole plasma appears to be involved in lasing. Separately treated are the cases of nanocrystals dispersed randomly in a matrix and that of heterostructures with ordered quantum dots (grown by Stranski–Krastanow method). Exciton and biexciton mechanisms of optical gain in quantum dots are analyzed. The crucial competing role of Auger recombination is expressed via the filling factor. Prospects of random lasing in semiconductor nanostructures are outlined.
John Hawthorne
- Published in print:
- 2006
- Published Online:
- September 2010
- ISBN:
- 9780199291236
- eISBN:
- 9780191710612
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199291236.003.0004
- Subject:
- Philosophy, Metaphysics/Epistemology
According to the doctrine of four-dimensionalism, our world and everything in it consists of stages or temporal parts; moreover, where an object exists at various times, it does so, according to the ...
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According to the doctrine of four-dimensionalism, our world and everything in it consists of stages or temporal parts; moreover, where an object exists at various times, it does so, according to the four-dimensionalist, in virtue of having distinct temporal parts at those times. While four-dimensionalism is often motivated by its purported solutions to puzzles about material objects and their persistence through time, it has also been defended by more direct arguments. Three such arguments stand out: (1) the argument from temporary intrinsic; (2) the argument from vagueness; and (3) the argument from recombination, Humean supervenience, and causal constraints. Each of these arguments originates in the work of four-dimensionalism's most prominent modern defender, David Lewis. The third of these arguments has received, by far, the least attention, critical or otherwise. This chapter addresses this imbalance.Less
According to the doctrine of four-dimensionalism, our world and everything in it consists of stages or temporal parts; moreover, where an object exists at various times, it does so, according to the four-dimensionalist, in virtue of having distinct temporal parts at those times. While four-dimensionalism is often motivated by its purported solutions to puzzles about material objects and their persistence through time, it has also been defended by more direct arguments. Three such arguments stand out: (1) the argument from temporary intrinsic; (2) the argument from vagueness; and (3) the argument from recombination, Humean supervenience, and causal constraints. Each of these arguments originates in the work of four-dimensionalism's most prominent modern defender, David Lewis. The third of these arguments has received, by far, the least attention, critical or otherwise. This chapter addresses this imbalance.
Michael L. Arnold
- Published in print:
- 2007
- Published Online:
- April 2010
- ISBN:
- 9780199229031
- eISBN:
- 9780191728266
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199229031.001.0001
- Subject:
- Biology, Evolutionary Biology / Genetics
Even before the publication of Darwin's Origin of Species, the perception of evolutionary change has been a tree-like pattern of diversification — with divergent branches spreading further and ...
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Even before the publication of Darwin's Origin of Species, the perception of evolutionary change has been a tree-like pattern of diversification — with divergent branches spreading further and further from the trunk. In the only illustration of Darwin's treatise, branches large and small never reconnect. However, it is now evident that this view does not adequately encompass the richness of evolutionary pattern and process. Instead, the evolution of species from microbes to mammals builds like a web that crosses and re-crosses through genetic exchange, even as it grows outward from a point of origin. Some of the avenues for genetic exchange, for example introgression through sexual recombination versus lateral gene transfer mediated by transposable elements, are based on definably different molecular mechanisms. However, even such widely different genetic processes may result in similar effects on adaptations (either new or transferred), genome evolution, population genetics, and the evolutionary/ecological trajectory of organisms. For example, the evolution of novel adaptations (resulting from lateral gene transfer) leading to the flea-borne, deadly, causative agent of plague from a rarely-fatal, orally-transmitted, bacterial species is quite similar to the adaptations accrued from natural hybridization between annual sunflower species resulting in the formation of several new species. Thus, more and more data indicate that evolution has resulted in lineages consisting of mosaics of genes derived from different ancestors. It is therefore becoming increasingly clear that the tree is an inadequate metaphor of evolutionary change. In this book, the author promotes the ‘web-of-life’ metaphor as a more appropriate representation of evolutionary change in all life-forms.Less
Even before the publication of Darwin's Origin of Species, the perception of evolutionary change has been a tree-like pattern of diversification — with divergent branches spreading further and further from the trunk. In the only illustration of Darwin's treatise, branches large and small never reconnect. However, it is now evident that this view does not adequately encompass the richness of evolutionary pattern and process. Instead, the evolution of species from microbes to mammals builds like a web that crosses and re-crosses through genetic exchange, even as it grows outward from a point of origin. Some of the avenues for genetic exchange, for example introgression through sexual recombination versus lateral gene transfer mediated by transposable elements, are based on definably different molecular mechanisms. However, even such widely different genetic processes may result in similar effects on adaptations (either new or transferred), genome evolution, population genetics, and the evolutionary/ecological trajectory of organisms. For example, the evolution of novel adaptations (resulting from lateral gene transfer) leading to the flea-borne, deadly, causative agent of plague from a rarely-fatal, orally-transmitted, bacterial species is quite similar to the adaptations accrued from natural hybridization between annual sunflower species resulting in the formation of several new species. Thus, more and more data indicate that evolution has resulted in lineages consisting of mosaics of genes derived from different ancestors. It is therefore becoming increasingly clear that the tree is an inadequate metaphor of evolutionary change. In this book, the author promotes the ‘web-of-life’ metaphor as a more appropriate representation of evolutionary change in all life-forms.
