Christina Gail John - Academia.edu (original) (raw)
Papers by Christina Gail John
Interspeech 2007, 2007
A possible existence of a regular temporal trend superimposed over the durational pattern of indi... more A possible existence of a regular temporal trend superimposed over the durational pattern of individual segments is explored in read continuous speech in the western Slavonic language of Czech. A short text read by 75 speakers was used to ascertain whether the contextually conditioned temporal variation would allow any phrasal tendencies to manifest. The data were normalized against the speakers' characteristics and against the intrinsic duration of individual phones. The results indicate that while the linear trendlines are regularly declining, the most reliable partial trend is phrase-final deceleration. Three more general non-linear trends are identified.
Theory and Practice of Object Systems, 1995
This paper, which is partly tutorial in nature, summarizes some basic research goals in the study... more This paper, which is partly tutorial in nature, summarizes some basic research goals in the study and development o f t yped objectoriented programming languages. These include both immediate repairs to problems with existing languages and the long-term development o f more exible and expressive, yet type-safe, approaches to program organization and design. The technical part of the paper is a summary and comparison of three object models from the literature. We conclude by discussing approaches to selected research problems, including changes in the type of a method from super class to sub class and the use of types that give information about the implementations as well as the interfaces of objects. Such implementation types seem essential for adequate typing of binary operations on objects, for example.
To a stirred THF solution of [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (204mg, 0.40 mmol), tBuC≡P (75 µ... more To a stirred THF solution of [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (204mg, 0.40 mmol), tBuC≡P (75 µl, 0.46 mmol) was added dropwise.. The colour of the solution changed from red/orange to deep purple. After 30 minutes the solvent was removed in vacuo and the resulting residue extracted with hexane. Evaporation of the solvent yielded complex 1 as a deep purple powder which was pure enough for further use. Yield 85 %. If required the complex could be further purified by recrystalliastion from hexane or pentane solution at-30°C. 1 H NMR (C 6 D 6 , rt) δ = 1.89 (s, 15H, C 5 Me 5), 1.71 (s, 9H, CMe 3); 13 C NMR (C 6 D 6 , rt) δ = 337.2 (d, P ≡C, 1 J PC = 113.3 Hz), 122.2 (s, C 5 Me 5), 52.5 (s, CMe 3), 34.6 (s, CMe 3), 13.0 (s, C 5 Me 5); 31 P NMR (C 6 D 6 , rt) δ = 509.0 (s); Elemental Analysis calc. (%) C 37.0 H 4.97 found C 36.7 H 5.03. Complex 2 was prepared in a similar manner from [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (74mg, 0.14 mmol), AdC≡P (30 mg, 0.17 mmol). 1 H NMR (C 6 D 6 , rt) δ = 2.25 (m, Ad), 2.07 (d, 0.3 Hz, Ad), 1.80 (s, C 5 Me 5), 1.72 (m, Ad); 13 C NMR
The Biological Bulletin, 1991
The ultrastructure of the radial neuromuscular system of the trachymedusa Liriope tetraphylla was... more The ultrastructure of the radial neuromuscular system of the trachymedusa Liriope tetraphylla was examined to determine the morphological substrate underlying crumpling behavior-the folding of the margin into the subumbrellar cavity by radial muscle contraction. These contractions are produced by the four smooth muscle bands that run the length of the peduncle and extend over the subumbrellar surface to the margin, along the radii. Axons are present in the radial system and attain appreciable density at the base of insertion of the peduncle; contact between this radial nerve net and the inner nerve ring may occur at the margin. Gap junctions were not encountered within the ectodermal radial system. These various observations are discussed with respect to the control of crumpling in this and other species of hydromedusae.
This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 w... more This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 was charged with examining the most challenging aspects of positron sources for linear colliders and antiproton sources for proton-antiproton colliders, and the secondary beams of interest to the physics community that will be available from the next generation of high-energy particle accelerators. The leading issues, limiting technologies, and most important R&D efforts of positron production, antiproton production, and secondary beams are discussed in this paper. A listing of T4 Presentations is included.
MRS Proceedings, 1993
ABSTRACTHeterogeneous nucleation and crystal growth on protein substrates are critical steps in b... more ABSTRACTHeterogeneous nucleation and crystal growth on protein substrates are critical steps in biological hard tissue formation. Self assembled monolayers can be derivatized with various organic functional groups to mimic the “nucleation proteins” for induction of mineral growth. Studies of nucleation and growth on SAMs can provide a better understanding of biomineralization and can also form the basis of a superior thin film deposition process. We demonstrate that micron-scale, electron and ion beam, lithographic techniques can be used to pattern SAMs with functional organic groups that either inhibit or promote mineral deposition. Patterned films of iron oxyhydroxide were deposited on the areas patterned with nucleation sites. Studies of the deposition kinetic of these films show that the surface indeed induces heterogeneous nucleation and that film formation does not occur via absorption of polymers or colloidal material formed homogeneously in solution. The nucleus interfacial ...
Perform a survey of the present status as well as the vision of the future promises of the variou... more Perform a survey of the present status as well as the vision of the future promises of the various electron-positron circular colliders. The colliders to be covered include those currently in operation, currently under construction, or envisioned as a possibility of the future, and in the US and abroad. Special emphasis should be placed on the clear identification of the beam physics limits and technological limits, and an examination of the extent that they have been address by past research or need to be addressed by future research. Identify new and promising ideas even though they may need additional work. These issues should be addressed for all the leading technical realizations of the circular positron-electron colliders. Finally, the group should summarize in a brief report the highest priority research topics for different technological realizations of circular electron-positron systems and give an approximate timetable for key R&D development [1]. The group is also asked to provide a comprehensive presentation to high-energy and accelerator physicists in plenary sessions during the Snowmass workshop.
The present B-factories PEP-II and KEKB have reached luminosities of 3-4x10 33 /cm 2 /s and deliv... more The present B-factories PEP-II and KEKB have reached luminosities of 3-4x10 33 /cm 2 /s and delivered integrated luminosity at rates in excess of 4fb-1 per month [1,2]. The recent turn on of these two B-Factories has shown that modern accelerator physics, design, and engineering can produce colliders that rapidly reach their design luminosities and deliver integrated luminosities capable of frontier particle physics discoveries. PEP-II and KEK-B with ongoing upgrade programs should reach luminosities of over 10 34 /cm 2 /s in a few years and with more aggressive improvements may reach luminosities of order 10 35 /cm 2 /s by the end of the decade. However, due to particle physics requirements, the next generation B-Factory may require significantly more luminosity. Initial parameters of a very high luminosity e + e-B-Factory or Super B-Factory (SBF) are being developed incorporating several new ideas from the successful operation of the present generation e + eaccelerators [3,4]. A luminosity approaching 10 36 cm-2 s-1 appears possible. Furthermore, the ratio of average to peak luminosity may be increased by 30% due to continuous injection. The operation of this accelerator will be qualitatively different from present e + ecolliders due to this continuous injection.
MARINE GEOLOGY, 2004
The Costa target areas exhibit the variability of slope instabilities needed to improve our under... more The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment. In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides.
The PEP-II B-Factory at SLAC has reached a luminosity of 4.6x10 33 /cm 2 /s and has delivered 94 ... more The PEP-II B-Factory at SLAC has reached a luminosity of 4.6x10 33 /cm 2 /s and has delivered 94 fb-1 of data to the BaBar physics detector by the end of May 2002. PEP-II has delivered over 309 pb-1 in 24 hours and over 6.35 fb-1 in one month. The accelerator physics issues for these performance levels include electron cloud, beam-beam effects, parasitic beam-beam collisions, and RF beam loading. Upgrades to PEP-II are underway to increase the luminosity to 2 to 4x10 34 /cm 2 /s by FY2007. The accelerator physics effects that must be dealt with during these upgrades include RF loading, multi-bunch feedback, IR beta function, bunch length reduction, and interaction region vacuum chamber upgrades.
Theoretical Computer Science, 2002
Optimistic contract signing protocols allow two parties to commit to a previously agreed upon con... more Optimistic contract signing protocols allow two parties to commit to a previously agreed upon contract, relying on a third party to abort or conÿrm the contract if needed. These protocols are relatively subtle, since there may be interactions between the subprotocols used for normal signing without the third party, aborting the protocol through the third party, or requesting conÿrmation from the third party. With the help of Mur', a ÿnite-state veriÿcation tool, we analyze two related contract signing protocols: the optimistic contract signing protocol of Asokan, Shoup, and Waidner, and the abuse-free contract signing protocol of Garay, Jakobsson, and MacKenzie. For the ÿrst protocol, we discover that a malicious participant can produce inconsistent versions of the contract or mount a replay attack. For the second protocol, we discover that negligence or corruption of the trusted third party may allow abuse or unfairness. In this case, contrary to the intent of the protocol, the cheated party is not able to hold the third party accountable. We present and analyze modiÿcations to the protocols that avoid these problems and discuss the basic challenges involved in formal analysis of fair exchange protocols.
The Astrophysical Journal, 2009
The Astrophysical Journal, 2005
We present HST/STIS and FUSE spectra of the QSO PG 1211+143 (z em = 0.081) and a galaxy survey of... more We present HST/STIS and FUSE spectra of the QSO PG 1211+143 (z em = 0.081) and a galaxy survey of the surrounding field. This sightline shows two strong intergalactic absorption systems at cz ≃ 15, 300 and 19,300 km s −1. This sightline addresses the nature and origin of the O VI absorbers, and their connection to galaxies. We explore the relationship of these absorbers to the nearby galaxies and compare them to other O VI-bearing absorbers in diverse environments. At 15,300 km s −1 , we find four distinct H I components and associated C II, C III, C IV, Si II, Si III, Si IV, N V, and O VI, lying near a spiral-dominated galaxy group with a bright member galaxy 137h −1 70 kpc from the sightline. The observed ions of C, Si, and N are likely to be photoionized, but the O VI is more consistent with collisional ionization. The ion ratios in this absorber resemble the highly-ionized Galactic HVCs; it may also trace the hot intragroup medium gas or the unbound wind of an undiscovered dwarf galaxy. At 19,300 km s −1 , we find five H I components and associated C III, Si III, and collisionally-ionized O VI lying 146h −1 70 kpc from an isolated galaxy. The properties of the O VI-bearing gas are consistent with an origin in strong shocks between low-metallicity gas (≥ 2 − 6 % solar) and one or more of the warm photoionized components. It is likely that these absorbers are related to the nearby galaxies, perhaps by outflows or gas stripped from unseen satellite galaxies by interactions. However, we cannot reject completely the hypothesis that they reside in the same large-scale structure in which the galaxies are embedded but are otherwise not directly related.
Stanford Law Review, 2002
Physics of Plasmas, 2000
A previous calculation [P. H. Diamond and T.-S. Hahm, Phys. Plasmas 2, 3640 (1995)] of the renorm... more A previous calculation [P. H. Diamond and T.-S. Hahm, Phys. Plasmas 2, 3640 (1995)] of the renormalized dissipation in the nonconservatively forced one-dimensional Burgers equation, which encountered a catastrophic long-wavelength divergence ∼kmin−3, is reconsidered. In the absence of velocity shear, analysis of the eddy-damped quasi-normal Markovian closure predicts only a benign logarithmic dependence on kmin. The original divergence is traced to an inconsistent resonance-broadening type of diffusive approximation, which fails in the present problem. Ballistic scaling of renormalized pulses is retained, but such scaling does not, by itself, imply a paradigm of self-organized criticality. An improved scaling formula for a model with velocity shear is also given.
Physics of Plasmas, 2000
Some aspects of low-frequency, long-wavelength fluctuations are considered. A stochastic model is... more Some aspects of low-frequency, long-wavelength fluctuations are considered. A stochastic model is used to show that power-law time correlations need not arise from self-organized criticality. A formula for the frequency spectrum of uncorrelated, overlapping avalanches is shown to be a special case of the spectral balance equation of renormalized statistical turbulence theory. It is argued that there need be no contradiction between the presence of long-time correlations and the existence of local transport coefficients.
Physics of Plasmas, 2000
Highly simplified models of random flows interacting with background microturbulence are analyzed... more Highly simplified models of random flows interacting with background microturbulence are analyzed. In the limit of very rapid velocity fluctuations, it is shown rigorously that the fluctuation level of a passively advected scalar is not controlled by the rms shear. In a model with random velocities dependent only on time, the level of cross-correlations between the flows and the background turbulence regulates the saturation level. This effect is illustrated by considering a simple stochastic-oscillator model, both exactly and with analysis and numerical solutions of the direct-interaction approximation. Implications for the understanding of self-consistent turbulence are discussed briefly.
Interspeech 2007, 2007
A possible existence of a regular temporal trend superimposed over the durational pattern of indi... more A possible existence of a regular temporal trend superimposed over the durational pattern of individual segments is explored in read continuous speech in the western Slavonic language of Czech. A short text read by 75 speakers was used to ascertain whether the contextually conditioned temporal variation would allow any phrasal tendencies to manifest. The data were normalized against the speakers' characteristics and against the intrinsic duration of individual phones. The results indicate that while the linear trendlines are regularly declining, the most reliable partial trend is phrase-final deceleration. Three more general non-linear trends are identified.
Theory and Practice of Object Systems, 1995
This paper, which is partly tutorial in nature, summarizes some basic research goals in the study... more This paper, which is partly tutorial in nature, summarizes some basic research goals in the study and development o f t yped objectoriented programming languages. These include both immediate repairs to problems with existing languages and the long-term development o f more exible and expressive, yet type-safe, approaches to program organization and design. The technical part of the paper is a summary and comparison of three object models from the literature. We conclude by discussing approaches to selected research problems, including changes in the type of a method from super class to sub class and the use of types that give information about the implementations as well as the interfaces of objects. Such implementation types seem essential for adequate typing of binary operations on objects, for example.
To a stirred THF solution of [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (204mg, 0.40 mmol), tBuC≡P (75 µ... more To a stirred THF solution of [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (204mg, 0.40 mmol), tBuC≡P (75 µl, 0.46 mmol) was added dropwise.. The colour of the solution changed from red/orange to deep purple. After 30 minutes the solvent was removed in vacuo and the resulting residue extracted with hexane. Evaporation of the solvent yielded complex 1 as a deep purple powder which was pure enough for further use. Yield 85 %. If required the complex could be further purified by recrystalliastion from hexane or pentane solution at-30°C. 1 H NMR (C 6 D 6 , rt) δ = 1.89 (s, 15H, C 5 Me 5), 1.71 (s, 9H, CMe 3); 13 C NMR (C 6 D 6 , rt) δ = 337.2 (d, P ≡C, 1 J PC = 113.3 Hz), 122.2 (s, C 5 Me 5), 52.5 (s, CMe 3), 34.6 (s, CMe 3), 13.0 (s, C 5 Me 5); 31 P NMR (C 6 D 6 , rt) δ = 509.0 (s); Elemental Analysis calc. (%) C 37.0 H 4.97 found C 36.7 H 5.03. Complex 2 was prepared in a similar manner from [TaCl 2 (CO) 2 (thf)(η 5-C 5 Me 5)] (74mg, 0.14 mmol), AdC≡P (30 mg, 0.17 mmol). 1 H NMR (C 6 D 6 , rt) δ = 2.25 (m, Ad), 2.07 (d, 0.3 Hz, Ad), 1.80 (s, C 5 Me 5), 1.72 (m, Ad); 13 C NMR
The Biological Bulletin, 1991
The ultrastructure of the radial neuromuscular system of the trachymedusa Liriope tetraphylla was... more The ultrastructure of the radial neuromuscular system of the trachymedusa Liriope tetraphylla was examined to determine the morphological substrate underlying crumpling behavior-the folding of the margin into the subumbrellar cavity by radial muscle contraction. These contractions are produced by the four smooth muscle bands that run the length of the peduncle and extend over the subumbrellar surface to the margin, along the radii. Axons are present in the radial system and attain appreciable density at the base of insertion of the peduncle; contact between this radial nerve net and the inner nerve ring may occur at the margin. Gap junctions were not encountered within the ectodermal radial system. These various observations are discussed with respect to the control of crumpling in this and other species of hydromedusae.
This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 w... more This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 was charged with examining the most challenging aspects of positron sources for linear colliders and antiproton sources for proton-antiproton colliders, and the secondary beams of interest to the physics community that will be available from the next generation of high-energy particle accelerators. The leading issues, limiting technologies, and most important R&D efforts of positron production, antiproton production, and secondary beams are discussed in this paper. A listing of T4 Presentations is included.
MRS Proceedings, 1993
ABSTRACTHeterogeneous nucleation and crystal growth on protein substrates are critical steps in b... more ABSTRACTHeterogeneous nucleation and crystal growth on protein substrates are critical steps in biological hard tissue formation. Self assembled monolayers can be derivatized with various organic functional groups to mimic the “nucleation proteins” for induction of mineral growth. Studies of nucleation and growth on SAMs can provide a better understanding of biomineralization and can also form the basis of a superior thin film deposition process. We demonstrate that micron-scale, electron and ion beam, lithographic techniques can be used to pattern SAMs with functional organic groups that either inhibit or promote mineral deposition. Patterned films of iron oxyhydroxide were deposited on the areas patterned with nucleation sites. Studies of the deposition kinetic of these films show that the surface indeed induces heterogeneous nucleation and that film formation does not occur via absorption of polymers or colloidal material formed homogeneously in solution. The nucleus interfacial ...
Perform a survey of the present status as well as the vision of the future promises of the variou... more Perform a survey of the present status as well as the vision of the future promises of the various electron-positron circular colliders. The colliders to be covered include those currently in operation, currently under construction, or envisioned as a possibility of the future, and in the US and abroad. Special emphasis should be placed on the clear identification of the beam physics limits and technological limits, and an examination of the extent that they have been address by past research or need to be addressed by future research. Identify new and promising ideas even though they may need additional work. These issues should be addressed for all the leading technical realizations of the circular positron-electron colliders. Finally, the group should summarize in a brief report the highest priority research topics for different technological realizations of circular electron-positron systems and give an approximate timetable for key R&D development [1]. The group is also asked to provide a comprehensive presentation to high-energy and accelerator physicists in plenary sessions during the Snowmass workshop.
The present B-factories PEP-II and KEKB have reached luminosities of 3-4x10 33 /cm 2 /s and deliv... more The present B-factories PEP-II and KEKB have reached luminosities of 3-4x10 33 /cm 2 /s and delivered integrated luminosity at rates in excess of 4fb-1 per month [1,2]. The recent turn on of these two B-Factories has shown that modern accelerator physics, design, and engineering can produce colliders that rapidly reach their design luminosities and deliver integrated luminosities capable of frontier particle physics discoveries. PEP-II and KEK-B with ongoing upgrade programs should reach luminosities of over 10 34 /cm 2 /s in a few years and with more aggressive improvements may reach luminosities of order 10 35 /cm 2 /s by the end of the decade. However, due to particle physics requirements, the next generation B-Factory may require significantly more luminosity. Initial parameters of a very high luminosity e + e-B-Factory or Super B-Factory (SBF) are being developed incorporating several new ideas from the successful operation of the present generation e + eaccelerators [3,4]. A luminosity approaching 10 36 cm-2 s-1 appears possible. Furthermore, the ratio of average to peak luminosity may be increased by 30% due to continuous injection. The operation of this accelerator will be qualitatively different from present e + ecolliders due to this continuous injection.
MARINE GEOLOGY, 2004
The Costa target areas exhibit the variability of slope instabilities needed to improve our under... more The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment. In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides.
The PEP-II B-Factory at SLAC has reached a luminosity of 4.6x10 33 /cm 2 /s and has delivered 94 ... more The PEP-II B-Factory at SLAC has reached a luminosity of 4.6x10 33 /cm 2 /s and has delivered 94 fb-1 of data to the BaBar physics detector by the end of May 2002. PEP-II has delivered over 309 pb-1 in 24 hours and over 6.35 fb-1 in one month. The accelerator physics issues for these performance levels include electron cloud, beam-beam effects, parasitic beam-beam collisions, and RF beam loading. Upgrades to PEP-II are underway to increase the luminosity to 2 to 4x10 34 /cm 2 /s by FY2007. The accelerator physics effects that must be dealt with during these upgrades include RF loading, multi-bunch feedback, IR beta function, bunch length reduction, and interaction region vacuum chamber upgrades.
Theoretical Computer Science, 2002
Optimistic contract signing protocols allow two parties to commit to a previously agreed upon con... more Optimistic contract signing protocols allow two parties to commit to a previously agreed upon contract, relying on a third party to abort or conÿrm the contract if needed. These protocols are relatively subtle, since there may be interactions between the subprotocols used for normal signing without the third party, aborting the protocol through the third party, or requesting conÿrmation from the third party. With the help of Mur', a ÿnite-state veriÿcation tool, we analyze two related contract signing protocols: the optimistic contract signing protocol of Asokan, Shoup, and Waidner, and the abuse-free contract signing protocol of Garay, Jakobsson, and MacKenzie. For the ÿrst protocol, we discover that a malicious participant can produce inconsistent versions of the contract or mount a replay attack. For the second protocol, we discover that negligence or corruption of the trusted third party may allow abuse or unfairness. In this case, contrary to the intent of the protocol, the cheated party is not able to hold the third party accountable. We present and analyze modiÿcations to the protocols that avoid these problems and discuss the basic challenges involved in formal analysis of fair exchange protocols.
The Astrophysical Journal, 2009
The Astrophysical Journal, 2005
We present HST/STIS and FUSE spectra of the QSO PG 1211+143 (z em = 0.081) and a galaxy survey of... more We present HST/STIS and FUSE spectra of the QSO PG 1211+143 (z em = 0.081) and a galaxy survey of the surrounding field. This sightline shows two strong intergalactic absorption systems at cz ≃ 15, 300 and 19,300 km s −1. This sightline addresses the nature and origin of the O VI absorbers, and their connection to galaxies. We explore the relationship of these absorbers to the nearby galaxies and compare them to other O VI-bearing absorbers in diverse environments. At 15,300 km s −1 , we find four distinct H I components and associated C II, C III, C IV, Si II, Si III, Si IV, N V, and O VI, lying near a spiral-dominated galaxy group with a bright member galaxy 137h −1 70 kpc from the sightline. The observed ions of C, Si, and N are likely to be photoionized, but the O VI is more consistent with collisional ionization. The ion ratios in this absorber resemble the highly-ionized Galactic HVCs; it may also trace the hot intragroup medium gas or the unbound wind of an undiscovered dwarf galaxy. At 19,300 km s −1 , we find five H I components and associated C III, Si III, and collisionally-ionized O VI lying 146h −1 70 kpc from an isolated galaxy. The properties of the O VI-bearing gas are consistent with an origin in strong shocks between low-metallicity gas (≥ 2 − 6 % solar) and one or more of the warm photoionized components. It is likely that these absorbers are related to the nearby galaxies, perhaps by outflows or gas stripped from unseen satellite galaxies by interactions. However, we cannot reject completely the hypothesis that they reside in the same large-scale structure in which the galaxies are embedded but are otherwise not directly related.
Stanford Law Review, 2002
Physics of Plasmas, 2000
A previous calculation [P. H. Diamond and T.-S. Hahm, Phys. Plasmas 2, 3640 (1995)] of the renorm... more A previous calculation [P. H. Diamond and T.-S. Hahm, Phys. Plasmas 2, 3640 (1995)] of the renormalized dissipation in the nonconservatively forced one-dimensional Burgers equation, which encountered a catastrophic long-wavelength divergence ∼kmin−3, is reconsidered. In the absence of velocity shear, analysis of the eddy-damped quasi-normal Markovian closure predicts only a benign logarithmic dependence on kmin. The original divergence is traced to an inconsistent resonance-broadening type of diffusive approximation, which fails in the present problem. Ballistic scaling of renormalized pulses is retained, but such scaling does not, by itself, imply a paradigm of self-organized criticality. An improved scaling formula for a model with velocity shear is also given.
Physics of Plasmas, 2000
Some aspects of low-frequency, long-wavelength fluctuations are considered. A stochastic model is... more Some aspects of low-frequency, long-wavelength fluctuations are considered. A stochastic model is used to show that power-law time correlations need not arise from self-organized criticality. A formula for the frequency spectrum of uncorrelated, overlapping avalanches is shown to be a special case of the spectral balance equation of renormalized statistical turbulence theory. It is argued that there need be no contradiction between the presence of long-time correlations and the existence of local transport coefficients.
Physics of Plasmas, 2000
Highly simplified models of random flows interacting with background microturbulence are analyzed... more Highly simplified models of random flows interacting with background microturbulence are analyzed. In the limit of very rapid velocity fluctuations, it is shown rigorously that the fluctuation level of a passively advected scalar is not controlled by the rms shear. In a model with random velocities dependent only on time, the level of cross-correlations between the flows and the background turbulence regulates the saturation level. This effect is illustrated by considering a simple stochastic-oscillator model, both exactly and with analysis and numerical solutions of the direct-interaction approximation. Implications for the understanding of self-consistent turbulence are discussed briefly.