bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficacy of a Hot Washing Process for Pretreated Yellow Poplar to Enhance Bioethanol Production
Authors: Nagle Nicholas J. , Elander Richard T. , Newman Mildred M. , Rohrback Brian T. , Ruiz Raymond O. , Torget Robert W.
Published: September 2002

Cost reductions for pretreatment and bioconversion processes are key objectives necessary to the successful deployment of a bioethanol industry. These unit operations have long been recognized for their impact on the production cost of ethanol. One strategy to achieve this objective is to improve the pretreatment process to produce a pretreated substrate resulting in reduced bioconversion time, lower cellulase enzyme usage, and/or higher ethanol yields. Previous research produced a highly digestible pretreated yellow poplar substrate using a multistage, continuously flowing, very dilute sulfuric acid (0.07% (w/v)) pretreatment. This process reduced the time required for the bioconversion of pretreated yellow poplar sawdust to ethanol. This resulted in a substantially improved yield of ethanol from cellulose. However, the liquid volume requirements, steam demand, and complexity of the flow‐through reactor configuration were determined to be serious barriers to commercialization of that process. A reconfigured process to achieve similar performance has been developed using a single‐stage batch pretreatment followed by a separation of solids and liquids and washing of the solids at a temperatures between 130 and 150 °C. Separation and washing at the elevated temperature is believed to prevent a large fraction of the solubilized lignin and xylan from reprecipitating and/or reassociating with the pretreated solids. This washing of the solids at elevated temperature resulted in both higher recovered yields of soluble xylose sugars and a more digestible pretreated substrate for enzymatic hydrolysis. Key operating variables and process performance indicators included acid concentration, temperature, wash volume, wash temperature, soluble xylose recovery, and performance of the washed, pretreated solids in bioconversion via simultaneous saccharification and fermentation (SSF). Initial results indicated over a 50% increase in ethanol yield at 72 h for the hot washed material as compared to the control (no washing, no separation) and a 43% reduction of in the bioconversion time required for a high ethanol yield from cellulose
Inhibition of Human Cell Apoptosis by Silkworm Hemolymph
Authors: Choi Shin Sik , Rhee Won Jong , Park Tai Hyun
Published: September 2002

Many studies on preventing apoptosis have been carried out from the viewpoint of anti‐apoptotic cloned‐gene expressions inside cells, whereas in this study, we investigated the inhibition of apoptosis by the addition of silkworm hemolymph, a natural compound, from outside of the cells. In a previous study, we reported the inhibition effect of silkworm hemolymph on the baculovirus‐induced insect cell apoptosis. Using the vaccinia virus‐HeLa cell system as a model system in this study, we found that silkworm hemolymph, the insect serum, inhibits apoptosis not only in the insect cell system but also in the human cell system. The vaccinia virus‐induced HeLa cell apoptosis was analyzed using DNA electrophoresis, TUNEL, and flow cytometry, and the resulting data confirmed that silkworm hemolymph inhibits human cell apoptosis. The inhibition of apoptosis due to silkworm hemolymph was not caused by an inhibition of virus binding and internalization steps, nor did silkworm hemolymph interfere with the virus production. The inhibition of apoptosis by silkworm hemolymph decreased the cell detachment from an adhering surface. With these characteristics, silkworm hemolymph can be effectively used to minimize cell death in commercial animal cell culture.
Nonlinear Dynamics of Regulation of Bacterial trpOperon: Model Analysis of Integrated Effects of Repression, Feedback Inhibition, and Attenuation
Authors: Xiu Zhi‐Long , Chang Zeng‐Yi , Zeng An‐Ping
Published: September 2002

The trpoperon encodes the five genes for the enzymes required to convert chorismate to tryptophan, and its switching on and off is controlled by both feedback repression and attenuation in response to different levels of tryptophan in the cell. Repression of the operon occurs when tryptophan concentration is high, and attenuation fine‐tunes the transcription level at a lower cellular concentration of tryptophan. An extended mathematical model is established in this study to describe the switching on and off of the trpoperon by considering the integrated effects of repression and attenuation. The influences of cell growth rate on the biosynthesis of tryptophan, stability and dynamic behavior of the trpoperon are investigated. Sustained oscillations of tryptophan levels are predicted from the regulated turning on and off of the trpoperon. It is interesting to note that during such oscillations the regulation of transcription displays a kind of “on” and “off” state in terms of gene expression, indicating the existence of a genetic circuit or switch in the regulation of the trpoperon. Time lags between transcription and translation are also predicted and may explain the occurrence of such oscillation phenomenon.
Process Design for Enzymatic Adipyl‐7‐ADCA Hydrolysis
Authors: Schroën Catharina Gerarda Petronella Henrica , Nierstrasz Vincent Adriaan , Bosma Rouke , Dijkstra Zwaantje Johanna , VandeSandt Emilius Johannes Albertus Xavierius , Beeftink Hendrik Harmen , Tramper Johannes
Published: September 2002

Adipyl‐7‐ADCA is a new source for 7‐aminodeacetoxycephalosporanic acid (7‐ADCA), one of the substrates for antibiotics synthesis. In this paper, a novel process for enzymatic 7‐ADCA production is presented. The process consists of a reactor, a crystallization step, a membrane separation step, and various recycle loops. The reactor can either be operated batch‐wise or continuously; with both types of processing high yields can be obtained. For batch reactors chemical degradation of 7‐ADCA can be neglected. For continuous reactors, chemical stability of 7‐ADCA is a factor to be taken into account. However, it was shown that the reaction conditions and reactor configuration could be chosen in such a way that also for continuous operation chemical degradation is not important. Downstream processing consisted of crystallization of 7‐ADCA at low pH, followed by a nanofiltration step with which, at low pH, adipic acid could be separated from adipyl‐7‐ADCA and 7‐ADCA. The separation mechanism of the nanofilter is based on size exclusion combined with charge effects. Application of this filtration step opens possibilities for recycling components to various stages of the process. Adipic acid can be recycled to the fermentation stage of the process while both adipyl‐7‐ADCA and 7‐ADCA can be returned to the hydrolysis reactor. In this way, losses of substrates and product can be minimized.
Mass Transfer and Hydrocarbon Biodegradation of Aged Soil in Slurry Phase
Authors: García‐Rivero M. , Saucedo‐Castañeda G. , de Hoyos S. Flores , Gutiérrez‐Rojas M.
Published: September 2002

Addition of toluene into slurry phase laboratory microcosm is proposed in order to increase desorption rate of hydrocarbons and as an alternative to improve bioavailability of hydrocarbon in aged soils. Our studies showed that toluene has a positive effect on desorption of total petroleum hydrocarbons (TPH). Addition of 14 000 mg toluene/kg of soil, in highly polluted soil, increased the consumption rate of hydrocarbons three times in comparison to control without solvent. In 30 days the initial TPH concentration in soil, 292 000 mg/kg, diminished 45%. Although toluene was able to dissolve complex organic compounds such as asphaltene fraction, it probably yielded a highly toxic toluene‐hydrocarbons phase. The inhibitory effect of toluene‐TPH was also studied. A substrate inhibition model was used: the kmand kiconstants were 57 and 490 mg TPH/L liquid phase, respectively. Experimental data were well described when the proposed model included sequential desorption and biodegradation phenomena. Damköhler number evaluation showed that rate of mass transfer was the limiting step in overall biodegradation in nonsolvent control. When high concentration of toluene was added, then bioreaction was the limiting step, but inhibitory effect should be considered. However, toluene addition at low concentrations facilitates the biodegradation of aromatic compounds.
Ultrasound‐Induced Stress Responses of Panax ginsengCells: Enzymatic Browning and Phenolics Production
Authors: Wu Jianyong , Lin Lidong
Published: September 2002

The stress metabolic activities of Panax ginseng( P. ginseng) cells induced by low‐energy ultrasound (US) were examined. P. ginsengcells in suspension cultures were exposed to 38.5 kHz US at two power levels (power density 13.7 and 61 mW/cm3) for 2 min. The US treatment caused rapid increase in the intracellular levels of polyphenol oxidase (PPO), peroxidase (PO), and phenylalanine ammonia lyase (PAL) and the production of polyphenols (PP) and phenolic compounds. The US‐induced enzyme activities and phenolics production are part of plant stress responses to a mechanical stimulus. The much higher PPO activity and rate of PP production in the sonicated cultures are correlated to enzymatic browning, suggestive of physical damage and membrane permeabilization of the cells by US. The cells after sonication also showed decreased water content and cell volume, which may also be attributed to US‐induced cell membrane permeabilization and water release. High‐pressure shock and fluid shear stress arising from acoustic cavitation were regarded as the major causes of the responses. Nevertheless, the US exposure caused only temporary cell growth depression but no net loss of biomass yield of the culture.
Carbon cash crop
Authors: Showstack Randy
Published: September 2002

Farms produce significant amounts of methane and nitrous oxide, and lesser amounts of carbon dioxide, all of which are greenhouse gases. A new publication from the U.S. Department of Agriculture (USDA) highlights measures some farmers already are taking to reduce greenhouse gases, and says that growing carbon as a crop can help farmers as well as the climate.

The report, “Growing Carbon,” says that providing credits to agricultural producers who increase their stores of carbon in the soil or in trees could be one way for countries to reduce carbon dioxide in the atmosphere and meet greenhouse gas emissions targets under potential domestic legislation or international climate agreements, such as the 1997 Kyoto Protocol.
USGS maps arsenic concentrations
Authors: Showstack Randy
Published: September 2002

About 10% of U.S. groundwater samples analyzed as part of a new U.S. Geological Survey (USGS) study exceed the World Health Organization's (WHO) guideline for arsenic in drinking water.

A USGS map of arsenic concentrations in groundwater across the U.S., released on May 8, shows the highest concentrations were found in samples taken from states in the Southwest and Rocky Mountain region, as well as in sections of the Midwest and Northeast.
Bids requested for Genesis Mission analytical facilities
Authors: Burnett Donald S.
Published: September 2002

The Genesis Discovery mission, to be launched in January 2001, will expose ultrapure materials to the solar wind for about 2 years and then return this sample to Earth for isotopic and chemical analysis in terrestrial laboratories.

Sample return missions use the best available instrumentation to achieve mission science goals. To complete the Genesis science objectives, advanced instrumentation that surpasses present laboratory sample analysis capabilities is required. Advanced Analytical Instrumentation Facilities (AAIFs) will be created for the mission to ensure that the best analytical instruments are used. This approach also enables broad participation by NASA scientists in solar wind sample return analysis.
Legislation may support STaRS
Authors: Anonymous
Published: September 2002

Congressman Vernon Ehlers (R, MI) has offered three bills in the House of Representatives that support K‐12 science, math, engineering, and technology (SMET) education (Eos, April 18, 2000). Although no dollar amounts are mentioned, the three bills contain numerous provisions for improving and expanding SMET education activities at the Department of Education and the National Science Foundation, and for tax incentives for pre‐service teacher education and in‐service professional development. Of particular interest is Section 15 of H.R. 4271, the National Science Education Act, which directs the NSF to provide scholarships for K‐12 teachers to participate in research programs in government agencies, colleges and universities, or private research establishments. Such scholarships could support AGU's Science Teacher and Research Scientist (STaRS) effort, which is intended to provide opportunities for teachers to participate in research under the direction of AGU scientists, and for those same scientists to participate in science teaching under the teachers' direction.
Roles of biology and gas exchange in determining the δ13C distribution in the ocean and the preindustrial gradient in atmospheric δ13C
Authors: Murnane R. J. , Sarmiento J. L.
Published: September 2002

We examine the processes responsible for the distribution of δ13C in a global ocean model. The dominant sources of gradients are biological processes and the temperature effect on isotopic fractionation. However, in a model without biology developed to examine the temperature effect of isotopic fractionation in isolation, we find an almost uniform δ13C distribution. Extremely slow δ13C air‐sea equilibration does not permit the surface ocean to come into equilibrium with the atmosphere and δ13C in the ocean thus becomes well mixed. However biological effects, which are interior to the ocean, are strongly expressed and minimally effected by air‐sea exchange. Biological fractionation thus dominates the oceanic δ13C distribution. An important feature of the model is an extremely large northward transport of isotopic anomaly. The transfer from the ocean to the Northern Hemisphere atmosphere of 120 Pg C ‰ is equivalent in magnitude to the signal that would be generated by a net terrestrial biospheric uptake of ≈ 5 Pg C yr−1 from the Northern Hemisphere atmosphere, or an ≈ l‐2‰ disequilibrium between terrestrial respiration and photosynthesis. Improved ocean model simulations and observational analysis are required to test for the possible existence of such a large oceanic transport of isotopic anomaly.
Extreme fractionation of gases caused by formation of clathrate hydrates in Vostok Antarctic Ice
Authors: Ikeda Tomoko , Fukazawa Hiroshi , Mae Shinji , Pepin Laurence , Duval Paul , Champagnon Bernard , Lipenkov Volodya Ya. , Hondoh Takeo
Published: September 2002

Atmospheric gases are trapped in ice sheets. These gases stored in air‐bubbles at shallower depth are gradually transformed into clathrate hydrates below the depth where the hydrostatic pressure exceeds the dissociation pressure of the clathrate hydrates. We measured Raman spectra of air‐bubbles and clathrate hydrates in Vostok Antarctic ice cores in order to determine the fractionation effects on the concentrations of gases during their transition process. The results showed variations of the N2/O2 ratios with depth. The average N2/O2 ratio in the air‐bubbles increases from the atmospheric value at the beginning of the transition to 11.7 at the end. The average N2/O2 ratio for the clathrate hydrates is 2.0 at the beginning, and asymptotically approaches the atmospheric value. This fractionation is attributed to faster diffusion of O2 than N2 through the ice lattice.
Interaction of pickup ions with quasi‐parallel shocks
Authors: Scholer M. , Kucharek H.
Published: September 2002

We have performed a number of numerical experiments to study the interaction of interstellar pickup protons and helium ions with quasi‐parallel stationary (bow) shocks and interplanetary traveling shocks. The collisionless shocks are modeled by the hybrid simulation method which treats the ions as macroparticles and the electrons as a massless background fluid. Solar wind protons, alpha particles, pickup H+ and He+ are included self‐consistently. The pickup ion distributions are modeled as spherical shells in velocity space convected with the solar wind. Pickup ions are rather efficiently reflected at both types of shocks. The reflection coefficient, measured as the ratio of incident to reflected ions, is more than one order of magnitude larger than the reflection coefficients for either solar wind protons or alpha particles, and is of the order of 30%. We have found that at high Mach number shocks pickup ions can reach many tens to over hundred times the plasma ramming energy in essentially one shock encounter. The reflected pickup ion distributions have a pancake‐type shape in velocity space.
The impact of mid‐depth recirculations on the distribution of tracers in the North Atlantic
Authors: Lozier M. Susan
Published: September 2002

An interesting feature of the waters carried equatorward by the Deep Western Boundary Current in the North Atlantic is their sharp vertical differentiation in tracer concentration and, accordingly, tracer age. In this work I demonstrate that the structure and lateral extent of the recirculations in the intermediate and deep North Atlantic have substantive differences with depth that can help explain the observed pattern of transient tracers such as tritium, ³He and CFCs. While recirculations are present at all depths spanned by the boundary current, the distinct tracer minimum occurs at the depth where the recirculation extent is maximized. Overall, the effect of the large‐scale recirculation at intermediate depths is to lengthen mixing pathways and to provide an alternate route for North Atlantic deep waters to enter the subtropical basin.
Augmentation of natural ionospheric plasma turbulence by HF heater waves
Authors: Lee M. C. , Klien E. M. C. , Burke W. J. , Zhang A. X. , Riddolls R. J. , Kuo S. P. , Sulzer M. P. , Isham B.
Published: September 2002

HF heating offers a powerful technique for controlled studies of ionospheric plasma turbulence. Heater waves generate large plasma density depletions and sheet‐like ionospheric irregularities in the F region, which can give rise to spread F backscatter. Electric fields associated with the induced irregularities can seed plasma instabilities, driven by such environmental causes as density gradients and ambient electric fields, to enhance spread F signatures. Significant reductions in the height‐integrated radar backscatter power, measured during the HF heating, indicate the depletion of magnetic flux tubes. Density gradients at the edges of the depletions provide new sources of free energy to augment ionospheric plasma turbulence, enhancing the spread F processes. Furthermore, depleted magnetic flux tubes create and/or alter ionospheric ducts thus affecting radio wave propagation.
The Oder Flood in July 1997: Transport routes of precipitable water diagnosed with an operational forecast model
Authors: Keil Christian , Volkert Hans , Majewski Detlev
Published: September 2002

A regional simulation of the severe precipitation episode which gave rise to the floods in the eastern part of Central Europe during July 1997 was performed using the meso‐β‐scale weather prediction model DM of Deutscher Wetterdienst. It is shown that the model reproduces the mesoscale precipitation distribution reasonably well as verified against available rain gauge observations. It is therefore used to investigate the transport routes of the bulk of moisture which led to the wide spread heavy precipitation. Inspection of the atmospheric water budget highlights the importance of the cyclonic advection of moist Mediterranean air for the formation of strong precipitation in Central Europe. Autochthonous influences are comparably small.
Improved Limb Atmospheric Spectrometer (ILAS) for stratospheric ozone layer measurements by solar occultation technique
Authors: Sasano Yasuhiro , Suzuki Makoto , Yokota Tatsuya , Kanzawa Hiroshi
Published: September 2002

The Improved Limb Atmospheric Spectrometer (ILAS) on board the Advanced Earth Observing Satellite (ADEOS) obtained 8 months of data for trace gas species from November 1996 to June 1997 for studies of the stratospheric ozone layer over the high‐latitude regions in both the Southern and Northern Hemispheres. The atmospheric parameters observed by ILAS were vertical profiles of ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, water vapor, aerosol extinction coefficient (at 780 nm), temperature, and pressure. Version 3.10 of the operational data processing algorithm was used to retrieve the corresponding geophysical profiles, which have been compared whenever possible with independent correlative measurements. Selected examples of ILAS products for ozone, nitric acid, and aerosol extinction coefficient (at 780 nm) are provided. The corresponding data is now publicly available for further analyses by the atmospheric community.
Comparison of TOMS and AVHRR volcanic ash retrievals from the August 1992 eruption of Mt. Spurr
Authors: Krotkov N. A. , Torres O. , Seftor C. , Krueger A. J. , Kostinski A. , Rose W. I. , Bluth G. J. S. , Schneider D. , Schaefer S. J.
Published: September 2002

On August 19, 1992, the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA‐12 and NASA's Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus‐7 satellite simultaneously detected and mapped the ash cloud from the eruption of Mt. Spurr, Alaska. The spatial extent and geometry of the cloud derived from the two datasets are in good agreement and both AVHRR split window IR (11–12µm brightness temperature difference) and the TOMS UV Aerosol Index (0.34–0.38µm ultraviolet backscattering and absorption) methods give the same range of total cloud ash mass. Redundant methods for determination of ash masses in drifting volcanic clouds offer many advantages for potential application to the mitigation of aircraft hazards.
A study of the energy balance climate model with CO2‐dependent outgoing radiation: Implication for the glaciation during the Cenozoic
Authors: Ikeda Takashi , Tajika Eiichi
Published: September 2002

We analyze the energy balance climate model with CO2‐dependent outgoing radiation, and obtain the steady‐state solution for very wide range of the atmospheric CO2 partial pressure and the thermal diffusion coefficient. We propose a phase diagram of the climate on the parameter space of the atmospheric CO2 and the thermal diffusion coefficient for the latitudinal heat transport, which may be useful to understand the climate change through the history of the Earth. It is shown that the formation of polar ice caps can be caused by decrease in the atmospheric CO2 and the latitudinal heat transport. The different history of glaciation in each hemisphere through the Cenozoic might be the result of difference in the heat transport in each hemisphere. Understanding of the small ice cap instability might be important to interpret the oxygen isotope record at the Eocene‐Oligocene boundary.
Vertical roughness of Mars from the Mars Orbiter Laser Altimeter
Authors: Garvin James B. , Frawley James J. , Abshire James B.
Published: September 2002

The vertical roughness of the martian surface at ∼250 m spatial scales has been determined in two global latitude bands: an equatorial and a high northern band acquired from 18 tracks of data by the Mars Orbiter Laser Altimeter (MOLA) during the Fall of 1997. The distribution of RMS vertical roughness, as derived from MOLA pulse widths, for the equatorial band is non‐gaussian, with an overall mean of 2.8 m RMS, but with secondary populations at 1.5 m and 2–6 m RMS. The higher latitude northern plains of Mars are almost uniformly ∼1 m RMS in their vertical roughness characteristics, suggesting that they are smoother than virtually any terrestrial deserts. We suggest that dust mantling has muted the local topography of Mars, rendering it as smooth as 1–2 m RMS. Heavily cratered uplands near the martian equator are noticeably rougher, indicating more rugged and less‐mantled local topography.
Tracking Polar Stratospheric Cloud Development with POAM II and a Microphysical Model
Authors: Steele H. M. , Drdla K. , Turco R. P. , Lumpe J. D. , Bevilacqua R. M.
Published: September 2002

The formation and development of polar stratospheric clouds are examined using a comprehensive microphysical model applied along air parcel trajectories. During Antarctic winter specific parcels are sampled over a time span of several days using extinction data from the POAM II satellite instrument. The observed evolution of polar stratospheric cloud spectral opacity is compared to predictions from model simulations. Hence, aerosol growth and decay in response to changing environmental conditions can be observed and interpreted. In some instances good agreement between observations and predictions has been obtained over periods of many days. The analysis provides evidence for the role of temperature history in cloud formation and properties, in agreement with previous studies. On occasion, the apparent behavior of a PSC along a trajectory is inconsistent with current theoretical concepts.
Current collection at the shuttle orbiter during the tethered satellite system tether break
Authors: Agüero V. M. , Burke W. J. , Gilchrist B. E. , Stone N. H. , Gentile L. C. , Williams S. D. , Cooke D. L. , Thompson D. C. , Bonifazi C. , Lebreton J.‐P.
Published: September 2002

We present measurements of currents, orbiter potentials, and plasma spectra during high‐voltage arcing coincident with the tether break event on the Tethered Satellite System reflight. In addition to the unexpectedly high tether currents observed, plasma spectra indicate the presence of ion and electron populations with broad energy ranges. These data were used in combination with satellite and orbiter current collection models to investigate the circuit behavior of the system's components. We find that arcing at the lower end of the tether supported the current flow in the tether during each phase of the break event, but with different mechanisms dominant depending on the location of the break point. With the break point inside deployer control structures, current arced to the orbiter ground, charging it to high negative potentials and allowing secondary ionization of neutral molecules near orbiter conducting surfaces. The most likely source of these neutrals is air trapped inside the tether at 1 atm of pressure that escaped through the hole in the tether insulation. When the break point was exposed to the exterior environment the tether current arced directly to the plasma. As long as the break point remained near the orbiter, the collection of electrons by conducting surfaces caused it to float at a low level of negative charging. The source of the energetic electrons detected in the payload bay remains uncertain. However, they can only have come from a region within the sheath that was more negatively charged than the orbiter's conducting surfaces.
AMPTE observations of mirror mode waves in the magnetosheath: Wavevector determination
Authors: Chisham G. , Schwartz S. J. , Balikhin M. A. , Dunlop M. W.
Published: September 2002

A unique method has been developed to completely determine the wavevector of a mirror mode wave using data from two closely spaced (separation less than wavelength/2) spacecraft. The method is based on the fact that mirror mode waves are linearly polarized and have zero frequency in the plasma rest frame. The method has been tested using Active Magnetospheric Particle Tracer Explorers United Kingdom Subsatellite (AMPTE UKS) and Ion Release Module (AMPTE IRM) high‐resolution magnetic field data from an interval of mirror mode waves observed in the middle magnetosheath on September 21, 1984. The results are also compared to those obtained using other methods of wavevector determination. The wavevectors estimated during the event are highly oblique to the ambient magnetic field direction as is expected from mirror wave theory. The application of the wavevector determination technique to further studies, such as studying the effect of finite electron temperature on mirror wave characteristics, is discussed.
Energetic electrons produced by lower hybrid waves in the cometary environment and soft X ray emission: Bremsstrahlung and K shell radiation
Authors: Shapiro V. D. , Bingham R. , Dawson J. M. , Dobe Z. , Kellett B. J. , Mendis D. A.
Published: September 2002

Electron acceleration by lower hybrid waves is a phenomenon well known in fusion studies (e.g., the so‐called lower hybrid current drive), and it is also responsible for electron energization in many space environments. In the latter case, lower hybrid wave turbulence is of a self‐generated type. It can be produced by the modified two‐stream instability (MTSI) of the counterstreaming ion populations resulting from the mass‐loading effect, for example, contamination of the solar wind flow or interstellar plasma with the newly born ions. In the cometary case analyzed in this paper these ions are produced by photoionization of the neutral gas outflow evaporated from the cometary nucleus. The interesting feature about lower hybrid oscillations is that they can be in simultaneous Cherenkov resonance with unmagnetized slow ions and fast but magnetized electrons, and owing to this, serve as a powerful tool for energy coupling leading to electron energization. In situ measurements at Comet Halley revealed the existence of intense lower hybrid turbulence inside the cometary bow shock. The quasi‐linear theory of the MTSI evolution constructed in this paper demonstrates a consistency of these wave measurements with the large flux of energetic electrons also measured during the encounter with Comet Halley. Energetic electrons penetrating inside the cometary atmosphere produce soft X ray emission by a combination of bremsstrahlung and line radiation of oxygen atoms. Theoretical results are found to be in good agreement with six independent observations of the X ray cometary emission by the Röntgen satellite and Beppo‐SAX telescopes.
Theory of plasma transport induced by low‐frequency hydromagnetic waves
Authors: Chen Liu
Published: September 2002

On the basis of the quasi‐linear limit of the nonlinear gyrokinetic equations we have derived self‐consistent, comprehensive theoretical results on plasma transport induced by low‐frequency hydromagnetic waves. Effects such as finite ion Larmor radii, realistic magnetic field geometries, general plasma equilibria, magnetic trapping, and arbitrary wave polarizations are included in the present analysis. Corresponding transport equations for flux tube‐averaged radial fluxes of particle, energy, and parallel momentum as well as local heating and parallel flow generation rates are obtained. The resultant transport coefficients exhibit the appealing physical pictures of exchanges of energies and momenta between resonant plasma particles and hydromagnetic wave quasi‐particles. The present results also indicate that radial transport generally consists of convective components in addition to the usual diffusive ones. Applications to the particle transport at the dayside magnetopause as well as the nonlinear saturation of drift Alfvén‐ballooning mode instabilities [Chen and Hasegawa, 1991] are also presented.
Substorm influence on the ionospheric electric potentials and currents
Authors: Weimer D. R.
Published: September 2002

Characteristic patterns of the high‐latitude, ionospheric electric potential have been derived for two groups, with and without the occurrence of magnetospheric substorms, and for all orientations of the interplanetary magnetic field (IMF). These maps were derived from all available, simultaneous Dynamics Explorer 2 and solar wind data, using a least error fit technique. There are distinctive patterns for each orientation of the IMF, both with and without substorms in progress. In comparison to the nonsubstorm electric potential patterns, the substorm group tends to have a more pronounced Harang discontinuity near midnight. The averages of the AE indices that were measured simultaneously with the electric potentials have also been analyzed. The AU index is found to be linearly proportional to the electric potential in the dusk cell, while the |AL| index compared with the dawn cell's potential has a nonlinear trend. The |AL| index is distinctively greater for the substorm group, as expected, while the electric potential and AU index remain relatively unchanged. The measured electric potential patterns have been combined with a conductivity model in order to derive ionospheric and field‐aligned currents. The Harang discontinuity is prominent in the horizontal ionospheric currents, particularly for the substorm group. Model calculations of |AL| indicate that some of the substorm increase can be accounted for by an enhanced auroral conductivity, while the changes in the electric field's magnitude and orientation near midnight, in distortions that do not significantly increase the overall potential drop, also contribute to the substorm electrojet. The field‐aligned currents show a systematic evolution of the region 1 and region 2 current belts as the IMF changes from a +Y to −Y orientation. For negative BY the upward currents form a continuous oval, linking the region 2 current on the dawn side with the region 1 current on the dusk side, through both noon and midnight. For positive BY the upward currents are no longer continuous through noon and are divided by downward current linking the region 2 current on the duskside with the region 1 current on the dawnside. The “region 0” or cusp currents, which move from prenoon to postnoon as the IMF BY changes from positive to negative, appear to be continuations of the post/prenoon region 1 current belts.
Interaction of the Saturnian magnetosphere with Titan: Results of a three‐dimensional MHD simulation
Authors: Kabin K. , Gombosi T. I. , De Zeeuw D. L. , Powell K. G. , Israelevich P. L.
Published: September 2002

The results of our three‐dimensional multiscale magnetohydrodynamic (MHD) model describing the interaction of Saturn's magnetosphere with Titan's upper atmosphere and exosphere are presented. The effects of a conducting ionosphere, exospheric mass loading and ion‐neutral charge exchange are taken into consideration. Because the ion gyroradius, in general, is not small compared to the radius of Titan the MHD approximation is not strictly applicable. However, it is still useful for the understanding of the general large‐scale features of the magnetospheric interaction. The upstream parameters are set for the typical case when Titan is inside the Saturnian magnetosphere. Although Titan certainly does not have a strong intrinsic magnetic field, some observed structures in Titan's wake might be explained by assuming the existence of a small intrinsic magnetic field. Thus we also considered the possibility that Titan has a small intrinsic dipole moment. The results of the simulations are compared with Voyager measurements and provide estimates of the total mass loading and the rate of ion‐neutral charge exchange. The simulation results reproduce the overall behavior of the observations, but it is clear that non‐MHD effects also play a role in the interaction between Saturn's magnetosphere and Titan.
Cosmic‐ray modulation and anisotropies at high rigidities: Theoretical modeling
Authors: Kóta József
Published: September 2002

The standard diffusion‐convection theory of cosmic‐ray transport is unable to properly describe solar modulation at the highest rigidities where the gyroradius and mean free path of particles become large and the diffusion picture breaks down. Present models need to invoke an ad hoc upper cutoff rigidity. We report on an attempt to extend the theoretical description of solar modulation to high rigidities, including the regime where diffusion approximation is not applicable. A scheme retaining the full directional distribution is outlined that includes scattering but does not rely upon the concept of diffusive streaming and thus remains valid at arbitrarily large values of the scattering mean free path. The scattering process is briefly discussed. We consider isotropic scattering and the simplest form of anisotropic scattering, but our formalism can accommodate more complex scattering processes as well. The application of the method is illustrated by numerical simulations obtained in a simplified two‐dimensional scenario which includes a flat heliospheric current sheet (HCS). We find that the anisotropies predicted in the inner heliosphere turn out to be largely independent of the conditions assumed at the outer boundary, and the anisotropies decrease gradually as the particle rigidity increases. Isotropic scattering gives rise to very small anisotropies in the inner heliosphere, where the solutions converge to an isotropic three‐dimensional (3‐D) force‐field solution. Anisotropic scattering, however, can produce reasonable anisotropies at the Earth's orbit. While the model is still greatly idealized and we do not attempt quantitative fits to observations at this stage, some important tendencies can already clearly be demonstrated. For instance, the polarity dependence of the solar diurnal variation is reproduced, the sense of the observed phase shift of the solar diurnal wave at polarity reversals of the sun is correctly predicted. The present two‐dimensional (2‐D) model fails to explain the sector‐dependent North–South anisotropy, which is a direct result of the wavy structure of the current sheet and cannot be interpreted in terms of a 2‐D model.
Inhomogeneous plasma flows: A review of in situ observations and laboratory experiments
Authors: Amatucci W. E.
Published: September 2002

Sheared flows in near‐Earth space plasmas, both magnetic‐field‐aligned and cross‐field, contribute to a rich array of phenomena which can be simulated in the laboratory. This has led to improved knowledge of the basic processes involving velocity shear operative in space, where it is not possible to conduct detailed and repeatable experiments with control over background parameters. Depending upon the flow characteristics, shear can contribute to either growth or damping of various plasma modes or, if sufficiently strong, can itself drive instabilities. These instabilities can have significant consequences in redefining the plasma equilibrium and can lead to energization and transport. A number of laboratory experiments have been performed to investigate the detailed physics associated with inhomogeneous space plasma flows. In this work, a review of in situ observations of processes associated with sheared flows and details of complementary laboratory experimental investigations is presented.
Energy spectra of 50‐keV to 20‐MeV protons accelerated at corotating interaction regions at Ulysses
Authors: Desai M. I. , Marsden R. G. , Sanderson T. R. , Lario D. , Roelof E. C. , Simnett G. M. , Gosling J. T. , Balogh A. , Forsyth R. J.
Published: September 2002

We analyze here the energy spectra of 50‐keV to 20‐MeV protons accelerated at corotating shocks observed at Ulysses in the southern heliosphere during 1992 and 1993. In general, our results are inconsistent with the predictions of two models based on diffusive shock acceleration theory (Fisk and Lee [1980] and Jones and Ellison [1991]). The main results are the following: (1) The relationships between the spectral indices and the shock compression ratio show significant departures from those predicted by the two models; the observed spectra are substantially harder than predicted; (2) the spectral indices at the reverse shocks depend strongly on the heliographic latitude of Ulysses; the hardest spectra are associated with strong quasi‐perpendicular shocks observed between 20°S and 30°S; (3) the spectral indices at the reverse shocks are anticorrelated with the upstream plasma velocity V′u in the de Hoffman‐Teller frame of the shock; and (4) the spectral indices at the forward shocks show no dependence on either the shock parameters or the heliographic latitude. The latitudinal dependence of the reverse shock spectra is probably related to the tilt (∼25°) of the heliospheric current sheet with respect to the solar equatorial plane during 1992 and 1993. The negative correlation between the spectral indices at the reverse shocks and V′u indicates that the gradient drift mechanism plays a crucial role in accelerating particles at corotating interaction regions (CIRs). The differences in our observations at the forward and reverse shocks may be due to the presence of a more energetic seed population and an enhancement in the level of magnetic field fluctuations upstream of the trailing edges of the CIRs.
Tidal despinning of the mantle, inner core superrotation, and outer core effective viscosity
Authors: Bills Bruce G.
Published: September 2002

Dissipation of tidal energy in the oceans causes a net transfer of angular momentum from the spin of the Earth to the relative orbital motions of the Moon and Sun. These torques couple directly to the mantle, and cause it to despin. Viscous coupling across the outer core is an effective means of communicating this change to the inner core. The Ekman time scale for dissipation of transient fluid motions associated with unsteady torques is much shorter than the time scale for adjustment of inner core and mantle rotational velocities in the steady Couette flow regime. The relative amplitude and phase of rotational variations in this system, with respect to the applied torques, are given in terms of core viscosity and torque variation frequency. Any short period variations in mantle torques will leave the inner core largely unchanged, and the influence of long period and secular torques applied to the mantle is efficiently transmitted to the inner core. The system response to a steady tidal torque applied to the mantle leaves the inner core with a small excess rotational velocity relative to the mantle, proportional to the product of outer core viscosity and the applied mantle torque. Recent estimates of an inner core super‐rotation of ˜1 degree/year imply an effective outer core viscosity of ˜103 Pa s. Glacial cycle variations in tidal torques somewhat complicate this picture, but do not yield significantly different viscosity estimates. However, they do imply that the differential rotation velocity varies by roughly a factor of 2 over a 100 kyr glacial cycle. The tidal shear strain may also contribute to development of anisotropy in the inner core.
Effect of thermal contrasts on gravity modeling at passive margins: Results from the western Barents Sea
Authors: Breivik Asbjørn Johan , Verhoef Jacob , Faleide Jan Inge
Published: September 2002

The western Barents Sea passive margin is a key locality to demonstrate the effect of the thermal structure of the lithosphere on forward gravity modeling. This margin developed by shear motion between the Eurasian and Greenland plates during the early Tertiary, and it is a significant border zone between young, hot oceanic lithosphere and cooler continental lithosphere. We construct two‐dimensional gravity models of 125 km thick lithosphere based on expansion of mantle rocks determined from thermal modeling. The approach has a substantial impact over traditional shallow gravity models, here demonstrated on a previously published model. On the basis of a 140 mGal free‐air anomaly, the old model proposes an anomalous, high‐density oceanic crust emplaced in a leaky transform adjacent to the continent during early margin development. However, the lithospheric models predict a homogeneous oceanic crust, while preserving regional isostasy at base lithosphere from continent to ocean. Two further tests agree with this conclusion: A map of Bouguer corrected ERS‐1 satellite data reveals no residual anomalies originating from the oceanic crust at the margin. Admittance analysis shows a strong oceanic lithosphere, and the high coherence between bathymetry and free‐air gravity discounts a significant subsurface load. The high gravity anomalies at the margin are thus an edge effect, enhanced by sedimentation onto the strong oceanic lithosphere, and shaped by the effect of the lithospheric thermal field. Other results of this work include a new continent‐ocean boundary map and two crustal transects across the margin.
S wave splitting in the aftershock region of the 1995 Hyogo‐ken Nanbu earthquake
Authors: Tadokoro Keiichi , Ando Masataka , Umeda Yasuhiro
Published: September 2002

The 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake; M7.2) occurred on January 17, 1995. A temporary aftershock observation was carried out by the Geophysical Research Group Organized by Universities for Prediction Seismology in 1995 from October 1995 to January 1996. A dense seismic network was deployed in and around the aftershock region, and some seismic stations were set directly on the active fault traces. We analyze the S wave splitting in and around the aftershock region of the Hyogo‐ken Nanbu earthquake. We detect a spatial variation of S wave splitting which can be related to crack orientations in an area where a large earthquake has occurred. At stations more than 1 km away from the Hyogo‐ken Nanbu earthquake fault zone, the leading shear wave polarization directions (LSPD) are found to be parallel to the axis of the regional maximum horizontal compressional stress (E‐W), suggesting that cracks caused by regional tectonic stress exist in the area. However, at stations within 500 m of the earthquake fault zones, the LSPDs are parallel to the fault strikes (N45°–50°E). This suggests that new fractures were produced parallel to the faults by shear faulting of the Hyogo‐ken Nanbu earthquake and resulted in S wave splitting along the earthquake fault zone. Nevertheless, shear fault origin anisotropy was not evident at stations on the active faults which ruptured in 1596. This implies that healing processes have already closed the fractures produced by shear faulting in 1596. Therefore we can expect that S wave splitting can be a useful tool for monitoring healing processes of active faults.
Pressure solution and viscous compaction in sedimentary basins
Authors: Fowler A. C. , Yang Xinshe
Published: September 2002

Mathematical models of compaction in sedimentary basins typically assume a relationship between effective pressure pe and porosity ϕ, which is of a non‐linear type; that is, pe = pe(ϕ). However, at depths greater than a kilometer, pressure solution becomes important and this relationship approaches a viscous one. We derive a mathematical model for viscous compaction in sedimentary basins and show how the model suggests different styles of behavior in the limits of slow and fast compaction.
Kinematics of the India‐Eurasia collision zone from GPS measurements
Authors: Larson Kristine M. , Bürgmann Roland , Bilham Roger , Freymueller Jeffrey T.
Published: September 2002

We use geodetic techniques to study the India‐Eurasia collision zone. Six years of GPS data constrain maximum surface contraction rates across the Nepal Himalaya to 18 ± 2 mm/yr at 12°N ±13° (1σ). These surface rates across the 150‐km‐wide deforming zone are well fitted with a dislocation model of a buried north dipping detachment fault striking 105°, which aseismically slips at a rate of 20 ± 1 mm/yr, our preferred estimate for the India‐to‐southern‐Tibet convergence rate. This is in good agreement with various geologic predictions of 18 ± 7 mm/yr for the Himalaya. A better fit can be achieved with a two‐fault model, where the western and eastern faults strike 112° and 101°, respectively, in approximate parallelism with the Himalayan arc and a seismicity lineament. We find eastward directed extension of 11 ± 3 mm/yr between northwestern Nepal Lhasa, also in good agreement with geologic and seismic studies across the southern Tibetan plateau. Continuous GPS sites are used to further constrain the style and rates of deformation throughout the collision zone. Sites in India, Uzbekistan, and Russia agree within error with plate model prediction.