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• 28641. [Article] Development, validation and the application of a congener specific photodegradation model for PBDEs

  The thermodynamic properties of 39 PBDEs have been calculated using Gaussian 03 on the B3LYP/6-31G(d)//B3LYP/6-31G(d) level. The PBDE congeners' enthalpies of formation increase with increasing number ...

  Citation × Citation Citation Abstract Copy Title: Development, validation and the application of a congener specific photodegradation model for PBDEs Author: Zeng, Xia The thermodynamic properties of 39 PBDEs have been calculated using Gaussian 03 on the B3LYP/6-31G(d)//B3LYP/6-31G(d) level. The PBDE congeners' enthalpies of formation increase with increasing number of bromines and show a strong dependence on the bromine substitution pattern. The effects of bromine substitution pattern have been quantitatively studied by GAM model based on the output of the theoretical calculations. Based on the GAM model, the enthalpies of formation of the 209 PBDE congeners were calculated. A photodegradation model was developed and validated to predict the products, and their relative concentrations, from the photodegradation of PBDEs. Photodegradation experiments were conducted for octa-BDE technical mixture and its individual components together with BDE-209, 184, 100, 99 and 47. Based on the results of the photodegradation experiments, as well as the model predictions, the photodegradation of PBDEs is a first order reaction and, further, the rate determining step is the stepwise loss of bromine. The predicted reaction time profiles of the photodegradation products correlate well with the experimental results. In addition, the photodegradation results were compared with anaerobic biodegradation. The PBDE products measured in the anaerobic biodegradation were found to be the major products in the photodegradation experiments. The photodegradation experiments and the model predictions were also compared with zero-valent iron reduction of BDE-209, 100 and 47 from a previous study and the same products were found in both photo and Fe⁰ degradation. Good correlation between 15 previously reported photodegradation rate constants of PBDE congeners and their calculated LUMO energies was found. This indicates that, similar to the Fe⁰ reduction, debromination by UV light is caused by electron transfer. Furthermore, the rate constants for the three different degradation processes are controlled by C-Br bond dissociation energy. The model was proved to be predictive for the photodegradation of PBDEs and it should be predictive for anaerobic biodegradation and Fe⁰ reduction of PBDEs. Title: Development, validation and the application of a congener specific photodegradation model for PBDEs Author: Zeng, Xia The thermodynamic properties of 39 PBDEs have been calculated using Gaussian 03 on the B3LYP/6-31G(d)//B3LYP/6-31G(d) level. The PBDE congeners' enthalpies of formation increase with increasing number of bromines and show a strong dependence on the bromine substitution pattern. The effects of bromine substitution pattern have been quantitatively studied by GAM model based on the output of the theoretical calculations. Based on the GAM model, the enthalpies of formation of the 209 PBDE congeners were calculated. A photodegradation model was developed and validated to predict the products, and their relative concentrations, from the photodegradation of PBDEs. Photodegradation experiments were conducted for octa-BDE technical mixture and its individual components together with BDE-209, 184, 100, 99 and 47. Based on the results of the photodegradation experiments, as well as the model predictions, the photodegradation of PBDEs is a first order reaction and, further, the rate determining step is the stepwise loss of bromine. The predicted reaction time profiles of the photodegradation products correlate well with the experimental results. In addition, the photodegradation results were compared with anaerobic biodegradation. The PBDE products measured in the anaerobic biodegradation were found to be the major products in the photodegradation experiments. The photodegradation experiments and the model predictions were also compared with zero-valent iron reduction of BDE-209, 100 and 47 from a previous study and the same products were found in both photo and Fe⁰ degradation. Good correlation between 15 previously reported photodegradation rate constants of PBDE congeners and their calculated LUMO energies was found. This indicates that, similar to the Fe⁰ reduction, debromination by UV light is caused by electron transfer. Furthermore, the rate constants for the three different degradation processes are controlled by C-Br bond dissociation energy. The model was proved to be predictive for the photodegradation of PBDEs and it should be predictive for anaerobic biodegradation and Fe⁰ reduction of PBDEs. Close

• 28642. [Article] Neutron shadow holography: a feasibility study

  Neutron shadow holography is a method of obtaining a three-dimensional neutron radiograph of an object using a Fresnel zone plate as an encoding aperture. The object is reconstructed by passing laser light ...

  Citation × Citation Citation Abstract Copy Title: Neutron shadow holography: a feasibility study Author: Coe, Douglas H. Neutron shadow holography is a method of obtaining a three-dimensional neutron radiograph of an object using a Fresnel zone plate as an encoding aperture. The object is reconstructed by passing laser light through a miniature copy of the radiograph. The technique has been applied extensively with X-rays and gamma rays but only recently with neutrons. This project is only the second known of its kind in the United States. The requirements for this type of work include the availability of an intense thermal neutron beam such as that produced by a nuclear research reactor, high resolution photo-reduction capability of up to 40 to 1, and high quality optics and laser equipment. In addition, the capability must exist to properly construct a zone plate encoding aperture. This project utilized all of the above facilities, equipment, and capabilities available at Oregon State University to successfully demonstrate the feasibility of performing neutron shadow holography experiments. An historical review is given of developments leading to the present state-of-art neutron holography technique. The physical properties and limitations of the classical Fresnel zone plate are extensively reviewed as they apply to shadow holography. The effect of the neutronic self-shielding properties of target objects on object resolution is discussed and shown to be generally the most limiting. Finally, contributions to the current literature on this subject are made in two areas. First, an improved zone plate construction method was successfully demonstrated which should substantially improve object reproducibility. Second, an analysis of the neutron energy spectrum effect on hologram quality is reported for the first time and shown to be substantial. Further refinement of the shadow holography technique at Oregon State University is necessary to achieve the level of success enjoyed by other researchers. This project has shown that such refinement is well within the capability of existing facilities and equipment. Title: Neutron shadow holography: a feasibility study Author: Coe, Douglas H. Neutron shadow holography is a method of obtaining a three-dimensional neutron radiograph of an object using a Fresnel zone plate as an encoding aperture. The object is reconstructed by passing laser light through a miniature copy of the radiograph. The technique has been applied extensively with X-rays and gamma rays but only recently with neutrons. This project is only the second known of its kind in the United States. The requirements for this type of work include the availability of an intense thermal neutron beam such as that produced by a nuclear research reactor, high resolution photo-reduction capability of up to 40 to 1, and high quality optics and laser equipment. In addition, the capability must exist to properly construct a zone plate encoding aperture. This project utilized all of the above facilities, equipment, and capabilities available at Oregon State University to successfully demonstrate the feasibility of performing neutron shadow holography experiments. An historical review is given of developments leading to the present state-of-art neutron holography technique. The physical properties and limitations of the classical Fresnel zone plate are extensively reviewed as they apply to shadow holography. The effect of the neutronic self-shielding properties of target objects on object resolution is discussed and shown to be generally the most limiting. Finally, contributions to the current literature on this subject are made in two areas. First, an improved zone plate construction method was successfully demonstrated which should substantially improve object reproducibility. Second, an analysis of the neutron energy spectrum effect on hologram quality is reported for the first time and shown to be substantial. Further refinement of the shadow holography technique at Oregon State University is necessary to achieve the level of success enjoyed by other researchers. This project has shown that such refinement is well within the capability of existing facilities and equipment. Close

• 28643. [Article] Photochemistry of some bromoarenes

  The photodebromination of selected bromoarenes has been studied at 300 nm to determine the the possible mechanistic pathways leading to product. Irradiation of 4-bromobiphenyl (BpBr) at this wavelength ...

  Citation × Citation Citation Abstract Copy Title: Photochemistry of some bromoarenes Author: Jang, Jung-suk The photodebromination of selected bromoarenes has been studied at 300 nm to determine the the possible mechanistic pathways leading to product. Irradiation of 4-bromobiphenyl (BpBr) at this wavelength leads to the product biphenyl. The quantum yield of intersystem crossing (0.98) and quenching studies with cis-1 ,3-pentadiene suggest that the reaction occurs only via the triplet state. The observed increase of quantum yield of reaction with increasing concentration of BpBr suggests formation of a triplet excimer between the triplet state and ground state of BpBr as the key reactive intermediate. The log of the rate constant for excimer formation showed a linear increase with solvent polarity. The correlation of rate constants for excimer formation with linear solvation energy parameters indicates only a weak polarization of the excimer species. In order to understand the extent of radical anion character in the excimer, the regiochemistry of the photo-debromination of 3,4-dibromobiphenyl (3,4-BpBr) was studied. 3,4-BpBr was irradiated with and without an electron donor (triethylamine). 3,4-BpBr was also chemically reduced with lithium biphenylide (LiDBB). The difference in the regiochemistries under these conditions has been interpreted in terms of reaction via a free radical anion in the case of reactions with triethylamine and LiDBB and a weakly polarized excimer in the case of direct irradiation. In order to understand the extent of polarization in the excimers and their conformation, it was decided to study systems where the structure of the molecule would fix the geometry of potential intramolecular charge-transfer complexes. Towards this goal, brominated [2.2]paracyclophanes, 4-bromo[2.2]para-cylophane (CpBr), pseudo-para-dibromo[2.2]cyclophane (ps-p-CpBr) and pseudo-ortho-dibromo[2.2]cyclophane (ps-o-CpBr), were studied. The effect of substitution pattern of the bromines on the efficiency of excimer formation was also investigated. The brominated [2.2]para-cyclophanes showed varying efficiencies of formation of intermolecular excimer and intramolecular charge-transfer. A probable conformation for the excimer from BpBr has been proposed based on these results. Title: Photochemistry of some bromoarenes Author: Jang, Jung-suk The photodebromination of selected bromoarenes has been studied at 300 nm to determine the the possible mechanistic pathways leading to product. Irradiation of 4-bromobiphenyl (BpBr) at this wavelength leads to the product biphenyl. The quantum yield of intersystem crossing (0.98) and quenching studies with cis-1 ,3-pentadiene suggest that the reaction occurs only via the triplet state. The observed increase of quantum yield of reaction with increasing concentration of BpBr suggests formation of a triplet excimer between the triplet state and ground state of BpBr as the key reactive intermediate. The log of the rate constant for excimer formation showed a linear increase with solvent polarity. The correlation of rate constants for excimer formation with linear solvation energy parameters indicates only a weak polarization of the excimer species. In order to understand the extent of radical anion character in the excimer, the regiochemistry of the photo-debromination of 3,4-dibromobiphenyl (3,4-BpBr) was studied. 3,4-BpBr was irradiated with and without an electron donor (triethylamine). 3,4-BpBr was also chemically reduced with lithium biphenylide (LiDBB). The difference in the regiochemistries under these conditions has been interpreted in terms of reaction via a free radical anion in the case of reactions with triethylamine and LiDBB and a weakly polarized excimer in the case of direct irradiation. In order to understand the extent of polarization in the excimers and their conformation, it was decided to study systems where the structure of the molecule would fix the geometry of potential intramolecular charge-transfer complexes. Towards this goal, brominated [2.2]paracyclophanes, 4-bromo[2.2]para-cylophane (CpBr), pseudo-para-dibromo[2.2]cyclophane (ps-p-CpBr) and pseudo-ortho-dibromo[2.2]cyclophane (ps-o-CpBr), were studied. The effect of substitution pattern of the bromines on the efficiency of excimer formation was also investigated. The brominated [2.2]para-cyclophanes showed varying efficiencies of formation of intermolecular excimer and intramolecular charge-transfer. A probable conformation for the excimer from BpBr has been proposed based on these results. Close

• 28644. [Article] Impacts of the Internet on academic culture in Aceh, Indonesia

  The adoption and increasing uses of the Internet in higher education in many parts of the world have resulted in fundamental changes in academic cultures. The transfer of information is essential to academic life, ...

  Citation × Citation Citation Abstract Copy Title: Impacts of the Internet on academic culture in Aceh, Indonesia Author: Daud, Darni M. The adoption and increasing uses of the Internet in higher education in many parts of the world have resulted in fundamental changes in academic cultures. The transfer of information is essential to academic life, and the Internet offers faster and easier access to information and communication between people than ever before. Since the effect of the Internet and the significance of the changes differs from one academic setting to another, it is important to study the impacts of the Internet on one particular academic community. This ethnographic study aims to examine the impacts of the Internet on the academic culture of higher education in Aceh, Indonesia. Data were collected by using ethnography, a method commonly employed in the examination of a culture. While this method consists mainly of interviews and observations, other techniques such as collection of related written materials (E-mail messages and/or communications), documents, and photos were used to supplement the data gathered from interviews and observations in Darussalam, the main campus of higher education in Aceh. Data collected from August 1996 through October 1998 revealed distinct themes in the Internet's impacts on the academic culture in Aceh. Findings of this study show that the Internet allows greater access to information, and facilitates communication, especially between students and faculty. The academics' interest in using the Internet builds a new and different academic culture. This new culture is more open to multiple schools of thought in different fields of study. While traditionally academics were isolated from dynamic knowledge development by their lack of access to information, today the Internet provides a bridge for Darussalam academia to the rest of the academic world. People now see that isolation weakens academic life, and are more open to pluralistic academic paradigms. Thus, the Internet changes the perception, performance, and daily activity in academia. This new culture tends to be democratic and to allow freedom in the development of teaching, learning, research, and other academic activities in Darussalam, Aceh. Title: Impacts of the Internet on academic culture in Aceh, Indonesia Author: Daud, Darni M. The adoption and increasing uses of the Internet in higher education in many parts of the world have resulted in fundamental changes in academic cultures. The transfer of information is essential to academic life, and the Internet offers faster and easier access to information and communication between people than ever before. Since the effect of the Internet and the significance of the changes differs from one academic setting to another, it is important to study the impacts of the Internet on one particular academic community. This ethnographic study aims to examine the impacts of the Internet on the academic culture of higher education in Aceh, Indonesia. Data were collected by using ethnography, a method commonly employed in the examination of a culture. While this method consists mainly of interviews and observations, other techniques such as collection of related written materials (E-mail messages and/or communications), documents, and photos were used to supplement the data gathered from interviews and observations in Darussalam, the main campus of higher education in Aceh. Data collected from August 1996 through October 1998 revealed distinct themes in the Internet's impacts on the academic culture in Aceh. Findings of this study show that the Internet allows greater access to information, and facilitates communication, especially between students and faculty. The academics' interest in using the Internet builds a new and different academic culture. This new culture is more open to multiple schools of thought in different fields of study. While traditionally academics were isolated from dynamic knowledge development by their lack of access to information, today the Internet provides a bridge for Darussalam academia to the rest of the academic world. People now see that isolation weakens academic life, and are more open to pluralistic academic paradigms. Thus, the Internet changes the perception, performance, and daily activity in academia. This new culture tends to be democratic and to allow freedom in the development of teaching, learning, research, and other academic activities in Darussalam, Aceh. Close

• 28645. [Article] Spatial and temporal patterns of windthrow in the Bull Run Watershed, Oregon

  Throughout the 20th century, windthrow has affected forests in the Bull Run watershed, a 26,500 ha basin that is the principal water source for the city of Portland, Oregon. Windthrow from storms in 1973 ...

  Citation × Citation Citation Abstract Copy Title: Spatial and temporal patterns of windthrow in the Bull Run Watershed, Oregon Author: Sinton, Diana Stuart Throughout the 20th century, windthrow has affected forests in the Bull Run watershed, a 26,500 ha basin that is the principal water source for the city of Portland, Oregon. Windthrow from storms in 1973 and 1983 was mapped into a geographic information system (GIS) and compared to a 1931 windthrow pattern that had been determined through field work and photo interpretation. By relating the windthrow patterns to vegetation, topography, soils, and edges created by forest canopy openings such as lakes and clearcuts, the degree to which these factors influence the patterns was tested with a logistic regression. Distanced sampling was used to compensate for spatial autocorrelation among the data. The results showed that topographic exposure most strongly affected the 1931 windthrow patterns, while a greater number of 1973 and 1983 windthrow patches were associated with clearcut edges than other edges, and those edges were more likely to be affected when located on shallow soils with a high hazard for windthrow. All three storms were characterized by northeasterly winds, a common occurrence during winter months in the vicinity of the Columbia River Gorge. However, the particular combination of at least two-consecutive days of severe east winds, and sub-freezing temperatures, had only occurred four times between 1948 and 1994, including both the 1973 and 1983 windthrow events. Multiple approaches were taken to estimate future windthrow risk in the Bull Run that incorporated both spatial and temporal variables. Probabilistic windthrow maps showing zones of low, medium, and high risk were generated for current forest conditions, as well as conditions projected-to the years 2010 and 2075. Because variables such as vegetation height and clearcut edges are ephemeral, the prediction of future risk incorporates assumptions of vegetation succession. However, a mean return interval calculated for predicted windthrow-generating storms suggests that such events could occur as frequently as once every three years. While no model can predict the precise location of a disturbance as variable as windthrow, an understanding of the relative spatial and temporal probability of windthrow provides useful information for forest planners and managers. Title: Spatial and temporal patterns of windthrow in the Bull Run Watershed, Oregon Author: Sinton, Diana Stuart Throughout the 20th century, windthrow has affected forests in the Bull Run watershed, a 26,500 ha basin that is the principal water source for the city of Portland, Oregon. Windthrow from storms in 1973 and 1983 was mapped into a geographic information system (GIS) and compared to a 1931 windthrow pattern that had been determined through field work and photo interpretation. By relating the windthrow patterns to vegetation, topography, soils, and edges created by forest canopy openings such as lakes and clearcuts, the degree to which these factors influence the patterns was tested with a logistic regression. Distanced sampling was used to compensate for spatial autocorrelation among the data. The results showed that topographic exposure most strongly affected the 1931 windthrow patterns, while a greater number of 1973 and 1983 windthrow patches were associated with clearcut edges than other edges, and those edges were more likely to be affected when located on shallow soils with a high hazard for windthrow. All three storms were characterized by northeasterly winds, a common occurrence during winter months in the vicinity of the Columbia River Gorge. However, the particular combination of at least two-consecutive days of severe east winds, and sub-freezing temperatures, had only occurred four times between 1948 and 1994, including both the 1973 and 1983 windthrow events. Multiple approaches were taken to estimate future windthrow risk in the Bull Run that incorporated both spatial and temporal variables. Probabilistic windthrow maps showing zones of low, medium, and high risk were generated for current forest conditions, as well as conditions projected-to the years 2010 and 2075. Because variables such as vegetation height and clearcut edges are ephemeral, the prediction of future risk incorporates assumptions of vegetation succession. However, a mean return interval calculated for predicted windthrow-generating storms suggests that such events could occur as frequently as once every three years. While no model can predict the precise location of a disturbance as variable as windthrow, an understanding of the relative spatial and temporal probability of windthrow provides useful information for forest planners and managers. Close

• 28646. [Article] The effects of light on photosynthesis and rooting of leafy cuttings of Pisum sativum L.

  The effects of light incident on leafy cuttings is quite complex because' light influences several factors which may affect root formation. One effect of light is to influence the carbohydrate status of ...

  Citation × Citation Citation Abstract Copy Title: The effects of light on photosynthesis and rooting of leafy cuttings of Pisum sativum L. Author: Davis, Tim D. The effects of light incident on leafy cuttings is quite complex because' light influences several factors which may affect root formation. One effect of light is to influence the carbohydrate status of the cutting by influencing photosynthesis. The role of current photosynthate in the rooting of leafy cuttings is uncertain. Accordingly I investigated the extent to which the supply of current photosynthate influences root formation on leafy cuttings of Pisum sativum L. When net photosynthesis was reduced to zero by maintaining the cuttings at the C0₂ compensation point or by blocking CO₂ exchange with an antitranspirant, rooting was reduced to about 50% of the controls. In addition to reducing rooting these treatments significantly reduced sucrose and glucose levels in the basal portion of the cuttings compared to controls. These experiments suggest that the supply of current photo- synthate can limit root formation. The above conclusions were supported by experiments using different photosynthetic photon flux densities and photoperiod lengths during rooting. Defoliation experiments also supported the role of current photosynthate in root formation. Defoliation of cuttings reduced rooting and carbohydrate levels in the base of the cuttings. Light incident on defoliated stems increased rooting and sucrose levels in the base of the stems. Dipping the defoliated cuttings in an antitranspirant blocked CO₂ fixation and almost completely inhibited root formation. These data suggest that stem photosynthesis also contributed to root formation. These experiments suggest that one of the major effects of light incident on leafy pea cuttings is to influence the amount of photosynthate available for root formation. It is difficult to establish whether current photosynthate influences rooting directly or indirectly by affecting some other factor(s) which control rooting. Whatever the case, treatments which influence photosynthesis influence rooting in a parallel manner. Title: The effects of light on photosynthesis and rooting of leafy cuttings of Pisum sativum L. Author: Davis, Tim D. The effects of light incident on leafy cuttings is quite complex because' light influences several factors which may affect root formation. One effect of light is to influence the carbohydrate status of the cutting by influencing photosynthesis. The role of current photosynthate in the rooting of leafy cuttings is uncertain. Accordingly I investigated the extent to which the supply of current photosynthate influences root formation on leafy cuttings of Pisum sativum L. When net photosynthesis was reduced to zero by maintaining the cuttings at the C0₂ compensation point or by blocking CO₂ exchange with an antitranspirant, rooting was reduced to about 50% of the controls. In addition to reducing rooting these treatments significantly reduced sucrose and glucose levels in the basal portion of the cuttings compared to controls. These experiments suggest that the supply of current photo- synthate can limit root formation. The above conclusions were supported by experiments using different photosynthetic photon flux densities and photoperiod lengths during rooting. Defoliation experiments also supported the role of current photosynthate in root formation. Defoliation of cuttings reduced rooting and carbohydrate levels in the base of the cuttings. Light incident on defoliated stems increased rooting and sucrose levels in the base of the stems. Dipping the defoliated cuttings in an antitranspirant blocked CO₂ fixation and almost completely inhibited root formation. These data suggest that stem photosynthesis also contributed to root formation. These experiments suggest that one of the major effects of light incident on leafy pea cuttings is to influence the amount of photosynthate available for root formation. It is difficult to establish whether current photosynthate influences rooting directly or indirectly by affecting some other factor(s) which control rooting. Whatever the case, treatments which influence photosynthesis influence rooting in a parallel manner. Close

• 28647. [Article] Funneled flow mechanisms in a sloping layered soil: Laboratory investigation

  This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: http://sites.agu.org/.

  Citation × Citation Citation Abstract Copy Title: Funneled flow mechanisms in a sloping layered soil: Laboratory investigation Author: Braddock, R. D., Selker, J. S., Steenhuis, T. S., Parlange, J.-Y., Kim, J.-S., Boll, J., Walter, M. T., Heilig, A. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: http://sites.agu.org/. Title: Funneled flow mechanisms in a sloping layered soil: Laboratory investigation Author: Braddock, R. D., Selker, J. S., Steenhuis, T. S., Parlange, J.-Y., Kim, J.-S., Boll, J., Walter, M. T., Heilig, A. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: http://sites.agu.org/. Close

• 28648. [Article] Optical and EPR investigations of the photochemistry of KCl:OH

  The hydroxide ion as a substitutional defect in KC1 can be photo-dissociated at liquid nitrogen temperature by ultraviolet light. The photochemistry of this system was investigated by EPR and optical absorption methods. ...

  Citation × Citation Citation Abstract Copy Title: Optical and EPR investigations of the photochemistry of KCl:OH Author: Bowen, Robert Clifford The hydroxide ion as a substitutional defect in KC1 can be photo-dissociated at liquid nitrogen temperature by ultraviolet light. The photochemistry of this system was investigated by EPR and optical absorption methods. Theoretical calculations were also performed in an investigation of the KC1:OH system. The bleaching behavior of photochemically colored KC1:OH was studied by simultaneous visible and EPR spectroscopy, and by broad range optical spectroscopy in the range from 185 nm to 2000 nm. The behavior of the system on warming from liquid nitrogen temperature to room temperature was also studied by the same methods. Pure KC1 crystals were colored with x- or gamma-rays at room temperature and studied by EPR and optical methods. The bleaching rate of photochemically colored KC1:OH was determined to be equivalent when measured by EPR or optical data. This result contradicted data reported previously. The disappearance of the EPR spectrum of ultraviolet irradiated KC1:OH at 250 K was correlated with optical data. This showed that the disappearance of the EPR was simultaneous with the conversion of H₂O⁻ centers to F centers. Results were presented and arguments given that the products and mechanism of the bleaching of H₂0⁻ centers were analagous to the products and mechanism of bleaching F centers. Approximate quantum mechanical calculations were performed which indicated that an exchange interaction of the unpaired F and 0⁻ electrons was not responsible for the disappearance of the EPR spectrum. Suggestions were made for further investigations which may yield information on the system. Title: Optical and EPR investigations of the photochemistry of KCl:OH Author: Bowen, Robert Clifford The hydroxide ion as a substitutional defect in KC1 can be photo-dissociated at liquid nitrogen temperature by ultraviolet light. The photochemistry of this system was investigated by EPR and optical absorption methods. Theoretical calculations were also performed in an investigation of the KC1:OH system. The bleaching behavior of photochemically colored KC1:OH was studied by simultaneous visible and EPR spectroscopy, and by broad range optical spectroscopy in the range from 185 nm to 2000 nm. The behavior of the system on warming from liquid nitrogen temperature to room temperature was also studied by the same methods. Pure KC1 crystals were colored with x- or gamma-rays at room temperature and studied by EPR and optical methods. The bleaching rate of photochemically colored KC1:OH was determined to be equivalent when measured by EPR or optical data. This result contradicted data reported previously. The disappearance of the EPR spectrum of ultraviolet irradiated KC1:OH at 250 K was correlated with optical data. This showed that the disappearance of the EPR was simultaneous with the conversion of H₂O⁻ centers to F centers. Results were presented and arguments given that the products and mechanism of the bleaching of H₂0⁻ centers were analagous to the products and mechanism of bleaching F centers. Approximate quantum mechanical calculations were performed which indicated that an exchange interaction of the unpaired F and 0⁻ electrons was not responsible for the disappearance of the EPR spectrum. Suggestions were made for further investigations which may yield information on the system. Close

• 28649. [Article] Seasonal and altitudinal regulation of embryonic and nymphal development in Allonemobius fasciatus (Orthoptera:Gryllidae)

  The physiological adaptations involved in the seasonal and altitudinal regulation of the life cycle in Allonemobius fasciatus were studied. This species maintains a univoltine life cycle with an embryonic diapause ...

  Citation × Citation Citation Abstract Copy Title: Seasonal and altitudinal regulation of embryonic and nymphal development in Allonemobius fasciatus (Orthoptera:Gryllidae) Author: Tanaka, Seiji The physiological adaptations involved in the seasonal and altitudinal regulation of the life cycle in Allonemobius fasciatus were studied. This species maintains a univoltine life cycle with an embryonic diapause over an altitudinal gradient of as large as 1,000 m. A more than 1.5 -month difference exists in hatching time between the highest and lowest altitudes studied. Little or no difference was detected among populations from different altitudes when various developmental traits such as diapause intensity, postdiapause development, and nymphal development, were compared in the laboratory. The photo periodic regulation of nymphal development seems to play an important role in compensating for the shorter growing season at higher elevations. The embryo of A. fasciatus showed seasonal variation in diapause characteristics. Diapause intensity measured as the duration of the egg stage at 20°C was greater in eggs laid early in the season than in those laid later. At 20°C, all embryos entered "winter diapause" at the end of the appendage-formation stage. However, when incubated at higher temperatures, another type of diapause was manifested before that stage. The higher the temperature the earlier was the stage at which this developmental suppression (called "summer diapause") was imposed. The induction of summer diapause depended not only upon the temperature of incubation but also upon the time of ovi-position. The capability of entering summer diapause at a high tem perature was decreased as the time of oviposition was delayed. The effects of temperature and moisture on embryonic development were examined using eggs with or without summer diapause and it is suggested that the role of summer diapause is not to ensure the survival of eggs under dry, warm conditions in summer but to avoid untimely hatching before winter, and to stabilize the univoltine life cycle in this species. Non-diapause development was induced when eggs were transferred from 20 to 27°C in early embryonic stages, although they entered diapause when constantly held at either of these temperatures. Based on this and other results, a model for the possible mechanism underlying the control of induction and intensity of diapause was proposed. Title: Seasonal and altitudinal regulation of embryonic and nymphal development in Allonemobius fasciatus (Orthoptera:Gryllidae) Author: Tanaka, Seiji The physiological adaptations involved in the seasonal and altitudinal regulation of the life cycle in Allonemobius fasciatus were studied. This species maintains a univoltine life cycle with an embryonic diapause over an altitudinal gradient of as large as 1,000 m. A more than 1.5 -month difference exists in hatching time between the highest and lowest altitudes studied. Little or no difference was detected among populations from different altitudes when various developmental traits such as diapause intensity, postdiapause development, and nymphal development, were compared in the laboratory. The photo periodic regulation of nymphal development seems to play an important role in compensating for the shorter growing season at higher elevations. The embryo of A. fasciatus showed seasonal variation in diapause characteristics. Diapause intensity measured as the duration of the egg stage at 20°C was greater in eggs laid early in the season than in those laid later. At 20°C, all embryos entered "winter diapause" at the end of the appendage-formation stage. However, when incubated at higher temperatures, another type of diapause was manifested before that stage. The higher the temperature the earlier was the stage at which this developmental suppression (called "summer diapause") was imposed. The induction of summer diapause depended not only upon the temperature of incubation but also upon the time of ovi-position. The capability of entering summer diapause at a high tem perature was decreased as the time of oviposition was delayed. The effects of temperature and moisture on embryonic development were examined using eggs with or without summer diapause and it is suggested that the role of summer diapause is not to ensure the survival of eggs under dry, warm conditions in summer but to avoid untimely hatching before winter, and to stabilize the univoltine life cycle in this species. Non-diapause development was induced when eggs were transferred from 20 to 27°C in early embryonic stages, although they entered diapause when constantly held at either of these temperatures. Based on this and other results, a model for the possible mechanism underlying the control of induction and intensity of diapause was proposed. Close

• 28650. [Article] A spatial analysis of factors influencing farmland conversion in the Bangkok metropolitan area, Thailand

  Agricultural land conversion is a complex process that involves a matrix of decisions and decision-makers. This study examines the nature and relative significance of spatial factors that influence the decisions ...

  Citation × Citation Citation Abstract Copy Title: A spatial analysis of factors influencing farmland conversion in the Bangkok metropolitan area, Thailand Author: Nathalang, Santita Agricultural land conversion is a complex process that involves a matrix of decisions and decision-makers. This study examines the nature and relative significance of spatial factors that influence the decisions of farmers who either sell farmland to developers for urban use or retain it for agricultural use. The conceptual model views farmers as boundedly rational individuals who seek satisfying economic and noneconomic returns from land. Their decisions are influenced by urban-generated factors that reflect land demand, by agricultural factors that determine the economic viability of agriculture under urban influences as well as by the decision-makers' characteristics. The study is done within the political and socioeconomic context of Bangkok, Thailand. The Thonburi region of the Bangkok Metropolitan Area is chosen as an example of a land use transition zone experiencing various urbanization pressures. Aerial photography is used to establish the location and magnitude of agricultural to urban land conversion between 1967 and 1983. Data from land use maps constructed from the air photo base maps and data from the Agricultural Census are used to test the research hypotheses of the study. The two primary research questions are: 1) Are the farmers' decisions to hold or to sell land related to urbanization pressures, economic viability of agriculture and farmers' characteristics?; and 2) What is the relative significance of these factors in influencing land conversion? Bivariate correlation and multiple regression analyses reveal the significant relationships of farmland conversion and the following variables: accessibility of land parcels, level of agricultural investment, age, education and occupational status. The dominant explanatory variables are the proximity to community centers and major roads. Secondary to them are the roles of farmers' age, education level and investment in irrigation. The effects of the other decision-maker's characteristics and agricultural variables are marginal but statistically significant. The study provides insight into the roles of agricultural viability as well as urban demand factors and decision-maker's characteristics in influencing the pace of land conversion in the developing country. Title: A spatial analysis of factors influencing farmland conversion in the Bangkok metropolitan area, Thailand Author: Nathalang, Santita Agricultural land conversion is a complex process that involves a matrix of decisions and decision-makers. This study examines the nature and relative significance of spatial factors that influence the decisions of farmers who either sell farmland to developers for urban use or retain it for agricultural use. The conceptual model views farmers as boundedly rational individuals who seek satisfying economic and noneconomic returns from land. Their decisions are influenced by urban-generated factors that reflect land demand, by agricultural factors that determine the economic viability of agriculture under urban influences as well as by the decision-makers' characteristics. The study is done within the political and socioeconomic context of Bangkok, Thailand. The Thonburi region of the Bangkok Metropolitan Area is chosen as an example of a land use transition zone experiencing various urbanization pressures. Aerial photography is used to establish the location and magnitude of agricultural to urban land conversion between 1967 and 1983. Data from land use maps constructed from the air photo base maps and data from the Agricultural Census are used to test the research hypotheses of the study. The two primary research questions are: 1) Are the farmers' decisions to hold or to sell land related to urbanization pressures, economic viability of agriculture and farmers' characteristics?; and 2) What is the relative significance of these factors in influencing land conversion? Bivariate correlation and multiple regression analyses reveal the significant relationships of farmland conversion and the following variables: accessibility of land parcels, level of agricultural investment, age, education and occupational status. The dominant explanatory variables are the proximity to community centers and major roads. Secondary to them are the roles of farmers' age, education level and investment in irrigation. The effects of the other decision-maker's characteristics and agricultural variables are marginal but statistically significant. The study provides insight into the roles of agricultural viability as well as urban demand factors and decision-maker's characteristics in influencing the pace of land conversion in the developing country. Close