bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and characterization of novel components of a Ca2+/calmodulin‐dependent protein kinase cascade in HeLa cells
Authors: Ishikawa Yumi , Tokumitsu Hiroshi , Inuzuka Hiroyuki , Murata-Hori Maki , Hosoya Hiroshi , Kobayashi Ryoji
Published: August 2003

In this report, we cloned a novel calmodulin‐kinase (CaM‐KIδ) from HeLa cells and characterized its activation mechanism. CaM‐KIδ exhibits Ca2+/CaM‐dependent activity that is enhanced (∼30‐fold) in vitro by phosphorylation of its Thr180 by CaM‐K kinase (CaM‐KK)α, consistent with detection of CaM‐KIδ‐activating activity in HeLa cells. We also identified a novel CaM‐KKβ isoform (CaM‐KKβ‐3) in HeLa cells whose activity was highly Ca2+/CaM‐independent. Transiently expressed CaM‐KIδ exhibited enhanced protein kinase activity in HeLa cells without ionomycin stimulation. This sustained activation of CaM‐KIδ was completely abolished by Thr180Ala mutation and inhibited by CaM‐KK inhibitor, STO‐609, indicating a functional CaM‐KK/CaM‐KIδ cascade in HeLa cells.
A novel ADP‐dependent DNA ligase from Aeropyrum pernix K1
Authors: Jeon Sung-Jong , Ishikawa Kazuhiko
Published: August 2003

A gene encoding a putative ATP‐dependent DNA ligase from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1 was cloned and the biochemical characteristics of the resulting recombinant protein were examined. The gene (accession no. APE1094) from A. pernix encoding a 69‐kDa protein showed a 39–61% identity with other ATP‐dependent DNA ligases from the archaea. Normally DNA ligase is activated by NAD+ or ATP. There has been no report about the other activators for DNA ligase. The recombinant ligase was a monomeric protein and catalyzed strand joining on a singly nicked DNA substrate in the presence of ADP and a divalent cation (Mg2+, Mn2+, Ca2+ and Co2+) at high temperature. The optimum temperature and pH for nick‐closing activity were above 70°C and 7.5°C, respectively. The ligase remained stable for 60 min of treatment at 100°C, and the half‐life was about 25 min at 110°C. This is the first report of a novel hyperthermostable DNA ligase that can utilize ADP to activate the enzyme.
Dynamic fluid‐kinetic (DyFK) modeling of auroral plasma outflow driven by soft electron precipitation and transverse ion heating
Authors: Wu X.‐Y. , Horwitz J. L. , Estep G. M. , Su Y.‐J. , Brown D. G. , Richards P. G. , Wilson G. R.
Published: August 2003

We apply a recently developed dynamic fluid‐kinetic (DyFK) model to simulate and investigate the effects of soft auroral electron precipitation and perpendicular ion heating by waves on the plasma outflow along auroral field lines. The DyFK model is constructed by coupling a fluid ionospheric model for the region from 120 to 800 km to a semikinetic treatment for topside through several RE altitude region. This approach, which is described in detail here, allows a partially self‐consistent description of the plasma transport along high‐latitude flux tubes where both low‐altitude ionospheric heating and ionization production and loss as well as high‐altitude energization and kinetic effects are incorporated and stressed. In the present work, we investigate the combined effects of the F region plasma production and electron heating by soft auroral electron precipitation and ion perpendicular wave heating at high altitudes, which produces ion conies. The auroral event simulated here involves 1.5 hours of moderate soft electron precipitation and relatively weak ion cyclotron waves along the magnetic field lines. The simulations reveal the F region electron heating and ionization by the soft electron precipitation, driving a topside O+ upflow of up to 109 cm−2 s−1 below 1000 km within 30 min after the electron precipitation is turned on. The enhanced O+ upflow plumes would be still gravitationally bound in the absence of further energization at higher altitudes. However, the synergistic effects of the increased upwelling ion supply driven by the precipitation and the wave‐driven ion heating at higher altitudes combine to enhance O+ bulk outflow by an order of magnitude above the baseline polar wind level to a net outflow flux of 108 ions cm−2 s−1 with a density of 10 ions cm−3 and bulk velocity of 12 km s−1 at 3 RE altitude. Various O+ conic velocity distributions develop within 10 min after transverse heating is initiated, and their characteristic energies saturate at approximately 10 eV for the peak wave‐induced heating rates of 10−14 ergs s−1 at 2 RE here. H+ is also affected by the increases of O+ due to H+–O+ collisional drag in the 1000 – 4000 km altitude transition region. H+ flow is much less affected by the wave heating because of the faster transit times through the high‐altitude wave heating zone and the lower H+ perpendicular heating rates which were incorporated here. The H+ bulk flow consists of a flux of 108 ions cm−2 s−1, a density of 4 ions cm−3, and a velocity of 30 km s−1 at 3 RE altitude.
He(23S) densities in the upper thermosphere: Updates in modeling capabilities and comparisons with midlatitude observations
Authors: Bishop James , Link Richard
Published: August 2003

Metastable He(23S) atoms in the upper day‐lit thermosphere can attain sufficiently high densities to be observed from the ground at twilight via resonant scattering of solar 1083 nm photons. Modeling the He(23S) density profile requires knowledge of neutral helium abundances, rates for excitation to the 23S metastable state, and transport coefficients for diffusion through the ambient atmosphere. In this paper, updates in the authors' modeling procedures are described. In particular, collision cross sections (total elastic scattering and momentum transfer) have been computed for He(23S) + He(11S) via partial wave expansion using realistic interaction potentials, from which the binary collision parameter has been calculated. He(23S) production via e−–He+ radiative recombination is also reassessed and compared with production by photoelectron impact. The role of diffusive transport in determining He(23S) density profiles is illustrated via comparative modeling of midlatitude, winter hemisphere data sets obtained under solar maximum and minimum conditions. These data‐model comparisons reveal the sensitivity of the modeling technique to geophysical quantities of interest (upper atmospheric He densities and photoelectron flux magnitudes) and identify remaining modeling uncertainties.
Equatorial and low latitude thermospheric winds: Measured quiet time variations with season and solar flux from 1980 to 1990
Authors: Biondi M. A. , Sazykin S. Y. , Fejer B. G. , Meriwether J. W. , Fesen C. G.
Published: August 2003

Thermospheric winds have been systematically determined at Arequipa, Peru, and Arecibo, Puerto Rico, from Fabry‐Perot interferometer measurements of Doppler shifts in the nightglow 630 nm line. The wind databases (1983 – 1990 at Arequipa and 1980 – 1990 at Arecibo) have been edited to eliminate measurements during geomagnetically disturbed conditions, then sorted by season and solar flux level. Following this, they were averaged to obtain the climatological behavior of the nighttime wind variations at the two locations. A new averaging technique, multivariate regression analysis, has been applied to the data, and the results compared to our prior binning averages. The observed wind behaviors at the Arequipa and Arecibo Observatories, which are at equal geographic latitudes on opposite sides of the equator, are contrasted to establish the seasonal flow patterns. The regression analysis results have then been compared with the predicted behavior provided by the National Center for Atmospheric Research's Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. In many cases, qualitative agreement between measurements and predictions is found as to wind directions and temporal variations, with differences in magnitude of ∼0–50 m/s. However, some striking differences are found that may arise from ionosphere‐thermosphere coupling effects. The overall results provide an important step in establishing the climatology of the thermospheric winds at equatorial and low‐latitude sites.
Evolution of mesoscale auroral cavities before substorm onset
Authors: Mäkelä J. S. , Mälkki A. M. , Koskinen H. E. J. , Clemmons J. H. , Erlandson R. E. , Holback B. , Eliasson L.
Published: August 2003

We have used density measurements made by the Freja satellite to analyze the dynamical behavior of mesoscale auroral cavities at an altitude of 1700 km. Freja's orbital period of 109 min enabled a very large data set of cavity occurrences to be collected. The occurrence distribution over 1 year was analyzed statistically, and two case studies of individual events were used to provide additional information. It was found that the data are consistent with persistence times of 2 or more hours for plasma cavities at this altitude. The statistical distribution also showed a weak but demonstrable correlation between cavity occurrence times and substorm onsets; this was also seen in the case studies, which both happened prior to substorm onsets. In the case studies, the motions of the cavities could be tracked with the support of ground data. It was found that the cavity followed the oval closely. As the oval moved southward during the substorm growth phase, the cavity also moved southward. When the expansion phase began, the data were consistent with the fact that the cavity expanded together with the oval. This suggests that the region where the cavities are observed is embedded within the auroral oval and can follow the motions of the oval.
Energetic particle observations near Ganymede
Authors: Paranicas C. , Paterson W. R. , Cheng A. F. , Mauk B. H. , McEntire R. W. , Frank L. A. , Williams D. J.
Published: August 2003

This paper combines data from the Galileo spacecraft plasma and energetic particle instruments. Data are included from two Ganymede flybys when the spacecraft was at northern Ganymede latitudes. Electron intensities from the two instruments are in very good agreement. Fits to 60 electron energy spectra are presented. We find the power of precipitating 0.5–3.0 keV electrons into both polar caps of Ganymede is ∼3 × 109 W. By assuming the instruments are intercalibrated, we infer that sulfur dominates the ion intensities at least in the tens of keV energy range. Furthermore, fits to the ion data indicate that the intensities are dominated by heavy ions below about 100 keV. Fits to these data are also used to estimate the sputtering rate of Ganymede's icy surface. It is found that ∼2 × 1026 water molecules/s are sputtered from Ganymede's polar caps which, when not redeposited on the surface, give an erosion rate of ∼8 m/Gyr.
Evolution of a strong shock in the distant heliosphere
Authors: Whang Y. C. , Lu J. Y. , Burlaga L. F.
Published: August 2003

The 1991 global merged interaction region (GMIR) shock is a strong forward shock observed from Voyager 2 on day 146 of 1991 at 34.6 AU at the leading edge of the 1991 GMIR. This shock is the strongest shock ever identified from the Voyager data in the distant heliosphere. In this paper we study the evolution and propagation of the 1991 GMIR shock outside 34.6 AU in the upwind direction taking into account the influence of interstellar pickup protons. We calculate the time, location, and various variables of this shock in the subsequent 400 days. We use the shock interaction model to develop a R,t‐simulation code to study this problem. The model treats the shock as a surface of discontinuity with zero thickness and uses the method of characteristics to study the evolution of the solar wind in the disturbed region. This model can accurately calculate the propagation speed and the strength of the shock. The numerical solution shows that as the GMIR shock propagates from 35 AU to 150 AU, the shock speed decreases monotonically from 543 km/s to 478 km/s and the density ratio decreases from 2.55 to 2.09. The solar wind proton temperature and the pickup proton temperature on two sides of the shock decrease monotonically with increasing heliocentric distance. Across the shock the solar wind proton temperature ratio is high, namely, ∼22 at 35 AU and ∼11.5 at 150 AU, while the pickup proton temperature ratio is an order of magnitude smaller: ∼2.1 at 35 AU and ∼1.8 at 150 AU.
Acceleration of the fast solar wind by the emergence of new magnetic flux
Authors: Fisk L. A. , Schwadron N. A. , Zurbuchen T. H.
Published: August 2003

Recent observations have shown that small magnetic loops are continuously emerging within supergranules in the solar photosphere. The subsequent reconnection of this emerging flux with field lines which open into the corona should define the Poynting's vector and mass flux into the corona. These two quantities uniquely determine the final energy flow and speed of the steady, fast solar wind. It is also pointed out that if the consequence of the emergence of new flux and its reconnection is lateral displacements of coronal magnetic field lines, this process should increase the magnetic field energy in the corona in a definable manner. The resulting dissipation of this energy, by work done on the plasma or by Joule heating, defines the spatial distribution for the heating of the corona. A simple model is constructed that yields profiles for the acceleration of the fast solar wind and for coronal temperatures that are reasonable.
On Europa's magnetospheric interaction: A MHD simulation of the E4 flyby
Authors: Kabin K. , Combi M. R. , Gombosi T. I. , Nagy A. F. , DeZeeuw D. L. , Powell K. G.
Published: August 2003

The global three‐dimensional interaction of Europa with the Jovian magnetosphere is modeled by using a complete set of ideal magnetohydrodynamic (MHD) equations. The model accounts for exospheric mass loading, ion‐neutral charge exchange, recombination, and a possible intrinsic dipole magnetic field of Europa. The single‐fluid MHD equations are solved by using a modern, finite volume, higher‐order, Godunov‐type method on an adaptively refined unstructured grid, which allows detailed modeling of the region near Europa while still resolving both the upstream region and the satellite's wake. The magnetic field and plasma density measured during Galileo's E4 flyby of December 19, 1996, are reproduced reasonably well in the simulation. We find the agreement between the data and our model particularly convincing if we assume that the plasma velocity during the E4 flyby deviated from the nominal corotation direction by approximately 20P. Evidence from the Galileo energetic particle detector also supports this assumption. In this case, we can fit the data using a dipole with orientation close to that of an induced dipole arising from the interaction of a hypothetical conducting subsurface layer on Europa with the periodically changing magnetic field of Jupiter. However, the magnitude of the dipole in our model is somewhat smaller (70%) than that suggested by Khurana et al. [1998]. The total mass loading and ion‐neutral charge exchange rates are consistent with the estimates of Europa's atmosphere and ionosphere.
Recent unrest and magma movements at Eyjafjallajökull and Katla volcanoes, Iceland
Authors: Sturkell Erik , Sigmundsson Freysteinn , Einarsson Páll
Published: August 2003

Katla and Eyjafjallajökull volcanoes are situated 25 km apart at the southern tip of the Eastern Volcanic Zone in Iceland. Both have been active in historic time (last 1100 years) and have a history of simultaneous activity. The much more active Katla volcano has erupted at least 20 times, and Eyjafjallajökull's two eruptions were contemporaneous with Katla eruptions. Following a quiet period of several decades, the seismicity beneath Eyjafjallajökull was high in 1994 and again in 1999. The activity culminated in July 1999 when a flash flood occurred from the Mýrdalsjökull ice cap covering Katla, associated with changes in seismicity, bursts of volcanic tremor, and the formation and deepening of ice cauldrons. We report here results of deformation observations of these events, both by GPS geodesy and tilt measurements. The 1999 increase in seismicity at Eyjafjallajökull was associated with significant inflation of the volcano. The deformation data are modeled by a point pressure source at 3.5 km depth beneath the flank of the volcano, about 4 km south of the summit crater. Maximum uplift of the model is 0.35 m. A similar model also explains deformation associated with the 1994 seismic crisis. The deformation field of the Katla volcano is more difficult to ascertain due to the extensive glacier coverage. Movements of points on nunataks on and near the caldera rim indicate inflation and magma movements at shallow level beneath the caldera in connection with the events of July 1999.
Sensitivity of δ15N of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean
Authors: Lourey Martin J. , Trull Thomas W. , Sigman Daniel M.
Published: August 2003

We report measurements of the δ15N of nitrate, suspended particulate nitrogen (PN), and sinking PN from cruises and moored sediment traps in the Subantarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia. As expected, surface water nitrate δ15N increased as nitrate was consumed during the spring/summer bloom. In contrast, the seasonal cycles of surface water suspended and sinking PN δ15N did not fit expectations from nitrate assimilation alone. Rather than increasing, the δ15N of surface suspended PN was relatively constant in the SAZ (at ∼1‰), and decreased during the summer in the PFZ (from ∼0 to ∼−4‰), most likely due to the production of low 15N PN by summertime ammonium recycling. Deep sediment trap PN δ15N also displayed seasonal decreases (from ∼4 to ∼1‰ in the SAZ, and from ∼3.5 to ∼0.5‰ in the PFZ), which correlated with PON flux magnitude. During high‐flux periods, exported PN δ15N values were close to expectations from nitrate‐based export, but low‐flux periods exhibited higher δ15N, consistent with either a reduction in the isotope effect of nitrate assimilation or more extensive isotopic alteration of the sinking material during low‐flux periods. The mass balance between net nitrate supply and exported PN that links sinking flux δ15N to nitrate utilization requires only that the annually integrated (rather than the seasonally varying) sinking flux of PN δ15N correlates with nitrate depletion. While a correlation between annually integrated sinking PN δ15N to nitrate depletion was observed in both the SAZ and PFZ, the sensitivity of sinking PN δ15N to nitrate depletion was lower than expected. Moreover, the seasonal observations raise the possibility that loss of the summertime high‐flux period represents an alternative explanation to increased nitrate utilization for the high sedimentary PN δ15N observed during glacial periods.
Patterns and controls of nitrous oxide emissions from waters draining a subtropical agricultural valley
Authors: Harrison John , Matson Pamela
Published: August 2003

Although nitrous oxide (N2O) emission from agricultural runoff is thought to constitute a globally important source of this greenhouse gas, N2O flux from polluted aquatic systems is poorly understood and scarcely reported, especially in low‐latitude (0°–30°) regions where rapid agricultural intensification is occurring. We measured N2O emissions, dissolved N2O concentrations, and factors likely to control rates of N2O production in drainage canals receiving agricultural and mixed agricultural/urban inputs from the intensively farmed Yaqui Valley of Sonora, Mexico. Average per‐area N2O flux in both purely agricultural and mixed urban/agricultural drainage systems (16.5 ng N2O‐N cm−2 hr−1) was high compared to other fresh water fluxes, and extreme values ranged up to 244.6 ng N2O‐N cm−2 hr−1. These extremely high N2O fluxes occurred during green algae blooms, when organic carbon, nitrogen, and oxygen concentrations were high, and only in canals receiving pig‐farm and urban inputs, suggesting an important link between land‐use and N2O emissions. N2O concentrations and fluxes correlated significantly with water column concentrations of nitrate, particulate organic carbon and nitrogen, ammonium, and chlorophyll a, and a multiple linear regression model including ammonium, dissolved organic carbon, and particulate organic carbon was the best predictor of [N2O] (r2 = 52%). Despite high per‐area N2O fluxes, our estimate of regional N2O emission from surface drainage (20,869 kg N2O‐N yr−1; 0.046% of N‐fertilizer inputs) was low compared to values predicted by algorithms used in global budgets.
Deep sea sedimentary analogs for the Vostok ice core
Authors: Mortyn P. Graham , Charles Christopher D. , Ninnemann Ulysses S. , Ludwig Kristen , Hodell David A.
Published: August 2003

Many applications of the Vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent Southern Ocean. Here we present oxygen isotopic records from high accumulation rate sites in the South Atlantic sector of the Southern Ocean, collected for the purpose of complementing the recently extended δD record from the Vostok ice core. The combination of several planktonic foraminiferal δ18O records from northern subantarctic piston cores demonstrates that all of the millennial‐scale oscillations expressed in the Vostok ice core over the last 60 ky are also present in marine records. The observations also support the assumption that the millennial‐scale oscillations common to both marine and ice archives are synchronous, thus providing a rationale for extending the marine‐ice core comparison through the last 400,000 years, making use of a marine drilled core (ODP Site 1089). By aligning the phase of these common abrupt events, we anchor the Vostok chronology to an orbitally tuned marine sediment chronology—a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and Antarctic polar climate. For example, this exercise suggests that, over at least the 4 major deglaciation events, the primary (orbital scale) changes in the chemistry and, most likely, the temperature of the deep Southern ocean were synchronous with changes in atmospheric pCO2 and polar air temperatures. We also find that the deuterium excess in the ice core resembles marine (foraminiferal) δ13C records and that the deuterium excess is synchronous with an “anomalous” foraminiferal δ18O signal (the residual between normalized versions of Vostok δD and foraminiferal δ18O). These observations demand a tight link between the Vostok isotopic record and the air‐sea interaction of the subantarctic zone.
Local time distribution of net field‐aligned currents derived from high‐altitude satellite data
Authors: Nakano S. , Iyemori T.
Published: August 2003

In order to explain features of geomagnetic disturbances observed at low and middle latitudes such as the dawn‐dusk asymmetry in the north‐south component, an antisunward current system has been proposed. The antisunward current system consists of net downward field‐aligned currents on the dayside, antisunward auroral electrojet currents, and net upward field‐aligned currents on the nightside. However, the net field‐aligned currents consisting in this current system have not been established by spacecraft observations yet. In order to discuss whether this antisunward current system actually exists or not and whether this current system actually causes the features of geomagnetic disturbances at low and middle latitudes or not, we statistically investigated the global structure of the geomagnetic disturbances generated by the field‐aligned currents in the inner magnetosphere by using the magnetic field data obtained by the DE‐1 satellite. On the basis of the results, local time distribution of the net field‐aligned currents was estimated. Net downward currents are found in the prenoon sector, and net upward currents are found in the premidnight sector. In the postnoon and the postmidnight sector, net field‐aligned currents are rather small on an average. The net downward field‐aligned currents in the prenoon would feed some portions of the auroral electrojets, and the portions would flow from the prenoon to the premidnight to connect with the net upward field‐aligned currents in the premidnight. These results are consistent with ground geomagnetic observations in the auroral region. In addition, we proposed a possible current system, which consistently explains our results and many other observations. It was also confirmed that the current system can actually cause the features of geomagnetic disturbances on the ground.
Observations of shock impact, disturbance dynamo effect, and a midlatitude large‐density depletion at 600 km altitude on the 17 April 2002 storm day
Authors: Su S.‐Y. , Chao C. K. , Yeh H. C. , Heelis R. A.
Published: August 2003

ROCSAT‐1 orbiting at 600 km altitude has observed a series of interesting topside ionospheric responses to the 17 April 2002 magnetic storm. After the impingement of the interplanetary shock, a Pi‐1 pulsation event in the plasma flow and ion density oscillations with a period of 19 s in the postnoon sector has been observed for less than 2 min. The storm induced disturbance dynamo effect is then observed an hour later with the postmidnight enhancement of the upward flow pattern described in the model of Scherliess and Fejer [1997] and the enhanced zonal flow pattern described in the models of Heelis and Coley [1992] and Scherliess et al. [2001]. However, the dynamo induced vertical electric field is noticed to be much weaker and decays faster than the induced eastward electric field in the postmidnight sector. A large‐density depletion is then observed at the end of this disturbance dynamo effect. It occurs at latitude 34°N (dip latitude 27°N) at the sunrise terminator. The density decreases about two orders of magnitude from the background level and the depletion width is about 500 km wide. An outward expanding flow up to 725 m/s is found inside the depletion. The NO+ ions found inside the depletion imply that the depletion was lifted‐up from the bottomside ionosphere in agreement with the observed large outward expanding flow. Large and rapid east‐west fluctuating flows up to 250 m/s are also observed together with large parallel flow variations of similar magnitude. The temperature inside the depletion is found increased to a peak value of 2050 K from the background temperature of 1200 K outside the depletion. However, this hottest temperature does not occur at the deepest density depletion. The observed temperature increase does not seem to fit in a proposed model of Oyama et al. [1988] where the heating comes from energy deposit of the fast electrons that are produced during the storm‐time and transported from the sunlit apex height at the equatorial region. The unfavorable reason is based on the ineffective energy exchanges between electrons and ions due to large ion mass and infrequent collisions between them at topside ionosphere. Furthermore, the observation fails to support the proposed inverse correlation between the temperature and the density. Instead, the temperature increase could come from the adiabatic heating by compressing ions along the flux tube from the equatorial region to high latitudes in the models of Heelis et al. [1978] and Bailey and Heelis [1980] in which the required large parallel flow has been observed.
An experimental and numerical study of the microstructural parameters contributing to the seismic anisotropy of rocks
Authors: Wendt Anke S. , Bayuk Irina O. , Covey‐Crump Stephen J. , Wirth Richard , Lloyd Geoffrey E.
Published: August 2003

The elastic properties of rocks are influenced by several microstructural variables, including the lattice preferred orientation and grain shape fabric of the mineral phases, variations in the spatial distribution of the mineral phases, the properties of the grain boundaries, and the presence of porosity/fractures. Consequently, in principle, directional variations in these variables can be inferred from seismic velocity anisotropy observations. Experimental seismic velocity measurements made on rocks of well‐characterized microstructure may be used to improve the quality of such interferences. However, since most rocks are microstructurally complex, in order to interpret the measurements fully, theoretical analyses which can accommodate all the relevant microstructural variables are required. Theoretical analyses of the requisite sophistication have only recently been developed. We have tested one of these (due to Ponte Castañeda and Willis) by using it to calculate the elastic properties of an upper mantle harzburgite and by then comparing the results with experimental velocity measurements to determine if the values of those microstructural variables which are difficult to quantify (grain boundary properties, fracture shape) are physically realistic. We find that they are and conclude that the Ponte Castañeda and Willis analysis provides a powerful method for a more detailed assessment of the causes of elastic property anistropy in rocks than has previously been possible.
Experimental validation and characterization of mean swash zone boundary conditions
Authors: Bellotti G. , Archetti R. , Brocchini M.
Published: August 2003

Performances of recently developed shoreline boundary conditions for wave‐averaged nearshore flow solvers are evaluated on the basis of available experimental data. Applications of the model to experimental data show the chosen equations suitably determine boundary values required for one‐dimensional mean flow. A detailed illustration is also given of the characteristics of flow properties which appear in the model. It is, finally, shown that very simple conditions can be suitably used at the mean shoreline of wave‐averaged flows for which boundary values of position, water depth, and velocity are computed on the basis of local quantities known at the seaward boundary of the swash.
Concentrations of dimethyl sulfide in the Strait of Georgia and its impact on the atmospheric sulfur budget of the Canadian West Coast
Authors: Sharma S. , Vingarzan R. , Barrie L. A. , Norman A. , Sirois A. , Henry M. , DiCenzo C.
Published: August 2003

A study was conducted in the Strait of Georgia to determine the seasonal variation of the biogenic sulfur budget, mainly dimethyl sulfide (DMS), during the three seasons, autumn (November 1999), spring (April 2000) and summer (August 2000). During autumn, surface DMS concentrations were low, 0.02–0.3 nmol l−1. They were highest during spring, 2–30 nmol l−1 and moderately high during summer, 0.2–14 nmol l−1. Related parameters such as chlorophyll a (chl a) and particulate or dissolved dimethyl sulphonioproprionate (DMSPp and DMSPd) were also measured. DMSPp levels were highest during spring coincident with the highest chl a concentrations. In contrast, DMSPd concentrations were highest during summer. Using the Liss‐Merlivat model for sea‐air gas exchange DMS fluxes to the atmosphere was calculated. The areal average DMS flux from the Strait of Georgia decreased from a maximum of 6.4 μmol m−2 d−1 during the spring to 2.2 μmol m−2 d−1 during the summer to 0.15 μmol m−2 d−1 during the autumn. DMS emissions from the Georgia Basin can contribute as much as 26% to the total sulfur emissions (natural and anthropogenic) from the region. Our results also indicate that biogenic sulfur emissions from the Pacific Ocean are also an important source of sulfur to the total regional sulfur budget for the Lower Fraser Valley and they will become more important as anthropogenic S emissions become better controlled.
Photon path length distributions inferred from rotating shadowband spectrometer measurements at the Atmospheric Radiation Measurements Program Southern Great Plains site
Authors: Min Qilong , Clothiaux Eugene E.
Published: August 2003

An algorithm for retrieving the first two moments of the photon path length probability density function for both the oxygen A‐band and the 0.820 μm water vapor band from measurements of the second generation Rotating Shadowband Spectrometer (RSS) is developed and applied to data from the Atmospheric Radiation Measurements (ARM) Program Southern Great Plains (SGP) site. In the algorithm, solar direct‐beam measurements are used to characterize the instrument response function in pixel (i.e., wavelength) space. By using nonlinear least squares regression with a two‐parameter gamma function constraint, the mean and variance of the photon path length probability density function for cloudy skies are subsequently retrieved from spectral measurements in both bands. Two case studies illustrate that the variance of the photon path length probability density function is more sensitive than the mean of the probability density function to vertical cloud structure. Interestingly, the first two moments of the photon path length probability density function appear to exhibit sufficient sensitivity to detect cirrus that the ARM SGP millimeter‐wave cloud radar failed to detect. Photon path length probability density functions from both the oxygen A‐band and 0.820 μm water vapor band provide additional insights into radiative transfer through a variety of cloudy conditions, improving our understanding of water vapor absorption of solar radiation in these conditions.
Radiative forcing of phytogenic aerosols
Authors: Barr J. G. , Fuentes J. D. , Bottenheim J. W.
Published: August 2003

The principal objective of this study is to investigate the radiative influences produced by phytogenic aerosols over a forested area in eastern Canada where measured aerosol concentrations resulted from α‐pinene and β‐pinene oxidation processes. The studied forest ecosystem produced moderate amounts of biogenic hydrocarbons, with isoprene and pinene mixing ratios reaching 1.6 parts per billion. Once oxidized, these pinene levels gave rise to maximum phytogenic aerosol concentrations of circa 5000 particles per cm3. The amount of diffuse and attenuated solar irradiance resulting from the interaction of aerosols with incoming irradiance was quantified using a one‐dimensional spectral radiative transfer model and measured aerosol sized distributions and concentrations. Results show that aerosols in the atmospheric boundary layer contributed to only moderate levels of diffuse irradiance but generated substantial attenuation of the incoming solar irradiance stream. For the irradiance levels measured in eastern Canada during cloudless days in July and with aerosol concentrations in the range of 2000 to 5000 particles per cm3, average daytime solar irradiance attenuation amounted to 0.04 W m−2 with a diffuse component of 0.01 W m−2. The maximum solar irradiance extinction reached 0.2 W m−2. Assuming a uniform spatial aerosol distribution, this negative radiative influence could offset substantial fractions of the regional thermal forcing resulting from increased levels of greenhouse gases such as carbon dioxide. It is concluded that greater radiative influences (cooling) could be present over regions dominated by hydrocarbon productive forest ecosystems.
Large eddy simulations of continental shallow cumulus convection
Authors: Zhu Ping , Albrecht Bruce
Published: August 2003

This paper addresses the basic physics underlying continental fair‐weather cumuli (FWC) and issues associated with the evolution of these clouds in response to the changes in external forcings and ambient meteorological conditions. To achieve the main objectives of this study, one FWC case observed from the Atmospheric Radiation Measurement (ARM) project at the southern Great Plains (SGP) site is simulated by a series of large‐eddy simulation (LES) experiments. For FWC forced by a strong buoyant convection due to large surface buoyancy fluxes, the mixed layer (ML) is usually associated with a moisture flux divergence in the vertical caused by the moisture discontinuity across the top of the convective boundary layer (CBL). Such a divergence is intimately related to cumulus initiation and development since it transports a large amount of moisture to an area above the mean ML where the forced FWC form and develop. The initiation of continental forced FWC results from thermal penetrations into the stable layer above. An important application of the penetration theory is to predict cumulus initiation. On the basis of the LES data, the authors developed a simple scheme that can be used to diagnose cumulus initiation using the variables that may be provided by large‐scale models, such as the Deardorff convective velocity scale, the mean ML height, the surface layer relative humidity, and the strength of the inversion. Unlike active marine shallow cumuli, the FWC focused on in this study are forced cumuli mainly supported by the buoyancy production in the ML. However, the simulations indicate that these clouds can have a significant impact on the turbulence intensity and transport in the CBL. Through sensitivity tests, the authors also studied the influence of the surface sensible and latent heat fluxes, the stratification above the CBL, the moisture difference across the top of the CBL, and the horizontal winds on the development of FWC and cloud radiative properties.
HDO in the mesosphere: Observation and modeling of novel isotopic variability
Authors: Sandor Brad J. , Clancy R. Todd
Published: August 2003

First measurements of [HDO]/[H2O] ratios in the lower mesosphere (50–70 km) are described. HDO and H2O abundances were obtained over the period 1992–2002, by ground‐based observation of microwave (λ ∼ 1.4 mm) spectral emission lines. Measured HDO depletions are highly variable, with δD values ranging from −58% ± 3% to −3% ± 9% (58% to 3% less deuterium than standard mean ocean water). Mesospheric δD values decrease with increasing H2O abundance. This is contrary to the stratospheric increase of δD with increasing H2O abundance, indicating that the physical mechanisms controlling mesospheric HDO depletion are fundamentally different from the mechanism (conversion of methane to water) known to control stratospheric HDO depletion. A photochemical model is used to show the observed mesospheric HDO depletion behavior is consistent with slower photolysis of HDO than of H2O. The difference in photolysis rates follows from a difference in cross sections of the two isotopomers at wavelengths >175 nm. Water photolysis in this spectral region is important only in the lower mesosphere. Therefore this mechanism for isotopic separation does not conflict with results of accepted stratospheric studies.
Ocean primary production and climate: Global decadal changes
Authors: Gregg Watson W. , Conkright Margarita E. , Ginoux Paul , O'Reilly John E. , Casey Nancy W.
Published: August 2003

Satellite‐in situ blended ocean chlorophyll records indicate that global ocean annual primary production has declined more than 6% since the early 1980's. Nearly 70% of the global decadal decline occurred in the high latitudes. In the northern high latitudes, these reductions in primary production corresponded with increases in sea surface temperature and decreases in atmospheric iron deposition to the oceans. In the Antarctic, the reductions were accompanied by increased wind stress. Three of four low latitude basins exhibited decadal increases in annual primary production. These results indicate that ocean photosynthetic uptake of carbon may be changing as a result of climatic changes and suggest major implications for the global carbon cycle.
Magnetic mirror structures observed by Cluster in the magnetosheath
Authors: Constantinescu O. D. , Glassmeier K.‐H. , Treumann R. , Fornaçon K.‐H.
Published: August 2003

We present a method for identification of magnetic mirror structures (MMS) in multi‐point spacecraft measurements and for deriving their full 3D geometry. Multiple minima in magnetic field data are no longer regarded as separate MMS but as belonging to the same mirror structure. The approach is based on fitting a model magnetic field to measured data from one or many spacecraft. Because of the complexity of the model magnetic field, fitting the data from only one spacecraft has proved not to be reliable even if data from the others spacecraft can be used for checking the results. The main reason is the instability of the numerical fit and the non‐uniqueness of the solution found. However, performing the fit on the data from multiple spacecraft allow the use of information from different regions of the structure eliminating false results and improving the numerical stability of the fit.
Interplate quasi‐static slip off Sanriku, NE Japan, estimated from repeating earthquakes
Authors: Uchida Naoki , Matsuzawa Toru , Hasegawa Akira , Igarashi Toshihiro
Published: August 2003

Space‐time distribution of quasi‐static slip on the plate boundary off Sanriku, northeastern (NE) Japan, was estimated by using small repeating earthquakes. We found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years. Based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area, we regarded these repeating events as creepmeters embedded on the plate boundary. The results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi‐static slips in the surrounding areas.
Methyl chloride and methyl bromide degradation in the Southern Ocean
Authors: Tokarczyk Ryszard , Goodwin Kelly D. , Saltzman Eric S.
Published: August 2003

This study presents shipboard measurements of the loss rate constants of methyl bromide and methyl chloride in surface seawater in the Southern Ocean, using a 13C stable isotope incubation technique. The measurements were made during October–December, 2001, on a cruise track extending from Hobart, Tasmania to Buchanan Bay (Mertz Glacier) at the coast of Antarctica (46–67°S, 138–145°E). Significant loss rates were measured for both compounds, even in very cold waters where chemical loss rates were negligible. These observations are attributed to biological uptake, and they explain the tendency for high latitude waters to be undersaturated with respect to atmospheric methyl bromide and methyl chloride. These observations are the first open ocean measurements demonstrating the biological degradation of methyl chloride.
Resistivity and microscopic characteristics of platinum in different structural states
Authors: Sokolenko V. I. , Starodubov Ya. D. , Mirny V. I. , Zavgorodniı̆ A. A. , Merisov B. A. , Kozinets V. V.
Published: August 2003

The experimental temperature dependence of the resistivity of platinum in different structural states is processed using the two-band Mott–Wilson model of a transition metal. It is found that impurities, deformation defects, and quenching defects have essentially different influences on the Debye temperature, the intensity of electron–electron Coulomb scattering, and the intensity of intra- and interband electron–phonon scattering. A number of effective microscopic characteristics and band parameters are calculated in the Friedel model. The mechanisms by which the different structural factors influence the investigated complex of physical characteristics of platinum are analyzed.
Quasiphase matched second-harmonic generation from periodic optical randomization of poled polymer channel waveguides
Authors: Martin G. , Ducci S. , Hierle R. , Josse D. , Zyss J.
Published: August 2003

We present experimental evidence of quasiphase-matched second harmonic generation in a polymer channel waveguide consisting of disperse red one (DR1) grafted to a poly(methylmethacrylate) (PMMA) main chain polymer at 30% molecular weight concentration. The ability of DR1 to photoisomerize is used to define a periodic segment of linear and nonlinear domains along the waveguide by photodepoling through a photolithographic mask of 10 μm periodicity, following quasiphase-matching requirements. A broad spectral scan between 1450 and 1800 nm evidences a peaked enhancement of second harmonic generation at 1536 nm, with experimental efficiency of 0.023% W−1, further compared to theoretical values. Wavelength dispersion of the quasiphase matched second harmonic peak as well as the penetration depth of the photodepoling beam in DR1 PMMA are also discussed.
Determination of free carrier bipolar diffusion coefficient and surface recombination velocity of undoped GaN epilayers
Authors: Aleksiejūnas R. , Sūdžius M. , Malinauskas T. , Vaitkus J. , Jarašiūnas K. , Sakai S.
Published: August 2003

Time-resolved nondegenerate four-wave mixing experiments were performed on 2.6-μm-thick GaN epilayers grown by metalorganic chemical-vapor deposition using picosecond pulses at 355 and 1064 nm for grating recording and probing, respectively. Measurements of free carrier grating kinetics at various grating periods Λ in range from 3 to 10 μm allowed determination of nonequilibrium carrier bipolar diffusion coefficient D=1.7 cm2/s at 300 K. Substitution of the D value into two-dimensional carrier transport model allowed fitting of the whole set of grating kinetics at various Λ varying surface recombination velocity S and linear recombination time τR. This procedure provided us a value of S=5×104 cm/s as well as carrier lifetime of ∼1 ns.
Dynamic orientation ratio in longitudinal recording media
Authors: Piramanayagam S. N. , Yin J. H. , Zhao H. B. , Kasim J. , Chen Y. J. , Zhang J. , Hee C. H.
Published: August 2003

The origin of orientation ratio (OR) in longitudinal recording media has been controversial in the literature. In the past, the observation of a higher OR for thinner magnetic films has been attributed to stress or thermal effects. Our measurements, carried out over a larger range of time scales, confirm that the thermal effects play a major role in the observation of a higher OR for thinner magnetic films. We point out that the OR is dynamic and follows a ln(t) behavior at larger time scales (5–1000 s). Our studies indicate that a larger OR and a more dynamic behavior of OR will be observed when KuV/kBT values are smaller. We also propose that the slope of dynamic OR can be used to compare the recording performance of media indirectly.
Electrochemical properties of carbon nanofiber web as an electrode for supercapacitor prepared by electrospinning
Authors: Kim C. , Yang K. S.
Published: August 2003

Poly(acrylonitrile) solutions in dimethylformamide were electrospun to be webs consisting of 300 nm ultrafine fibers. The webs were oxidatively stabilized and activated by steam resulting in activated carbon nanofibers (ACNFs). The specific surface area of the ACNF activated at 700 °C was the highest but mesopore volume fraction of that was lowest. On the other hand, the ACNFs activated at 800 °C showed opposite trends to those activated at 700 °C. The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (173 F/g at 10 mA/g). The elevated volume fraction of mesopores gave maximum specific capacitance at high current density (120 F/g at 1000 mA/g). The behavior is explained on the basis of ion mobility in the pores.
Dynamical behavior of a bistable chiral quasihomeotropic liquid crystal cell
Authors: Hsieh Chih-Yung , Chen Shu-Hsia
Published: August 2003

The dynamical behavior of the directors in a bistable chiral quasihomeotropic (BCQH) liquid crystal cell has been investigated. This cell can be switched from the initial quasihomeotropic configuration state at zero field to two static twisted states at 14 V by different switching processes. We studied the dynamic behavior of the BCQH cell based on the general nematohydrodynamic theory, and the detailed dynamical mechanism was illustrated by analyzing the director and velocity profiles obtained from the numerical simulation. We found that, in addition to the flow effect, the asymmetric polar-alignment condition is another important factor to achieve the switching bistability of our BCQH cell. The experimental and numerical results are reported in this letter.