bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid flow partitioning between fractures and a permeable rock matrix
Authors: Matthäi Stephan K. , Belayneh Mandefro
Published: March 2004

Field data‐based finite‐element simulations of flow partitioning between fractures and a permeable rock matrix reveal critical fracture aperture values that mark the transition from matrix to fracture dominated flow. For matrix permeabilities of 0.00 1–1 D, the matrix either dominates or contributes significantly to the total flow. The percentage of the flow‐normal cross‐section that is occupied by fractures, Af, strongly influences the fracture‐matrix permeability ratio, above which fractures will dominate flow. This ratio is 102–104 for Af = 10−4–10−3 (mean = 5 × 10−3), but also depends on the proportion of fractures which fully penetrate the representative elementary volume. Fluid‐velocity spectra for the fractured rock have three important characteristics: (1) Darcy velocity is only poorly correlated with permeability, (2) flow velocities have characteristic values, even if fracture‐length frequency relations are self similar, and (3) fracture and matrix velocities overlap.
Life of the Bellingshausen plate
Authors: Eagles Graeme , Gohl Karsten , Larter Robert D.
Published: March 2004

The onset of independent Bellingshausen plate movement in the South Pacific is estimated at just after chron C33o. This event closely follows a change in the offset sense on the transform arm of the Late Cretaceous Pacific‐Phoenix‐Antarctic triple junction and accompanies the creation and/or lengthening, by different mechanisms, of long‐offsets on the Pacific‐Antarctic ridge at the Udintsev, Tharp, Heezen and V transforms, as the triple junction stepped away from the ridge. At around chron C27, the Bellingshausen plate ceased to move independently and the Pacific‐Antarctic ridge inherited the set of long offset transforms. Shortly afterwards, the gravity fabric on the flanks of much of the ridge displays evidence for a spreading rate decrease possibly related to transpression on the long‐offset transforms. We speculate on a link between these events and regional tectonic changes around chron C27.
Raman lidar measurement of water vapor and ice clouds associated with Asian dust layer over Tsukuba, Japan
Authors: Sakai Tetsu , Nagai Tomohiro , Nakazato Masahisa , Matsumura Takatsugu
Published: March 2004

The vertical distributions of particle extinction, backscattering, depolarization, and water vapor mixing ratio were measured using a Raman lidar over Tsukuba (36.1°N, 140.1°E), Japan, on 23–24 April 2001. Ice clouds associated with the Asian dust layer were observed at an altitude of ∼6–9 km. The relative humidities in the cloud layer were close to the ice saturation values and the temperature at the top of the cloud layer was ∼−35°C, suggesting that the Asian dust acted as ice nuclei at the high temperatures. The meteorological analysis suggested that the ice‐saturated region was formed near the top of the dust layer where the moist air ascended in slantwise fashion above the cold‐frontal zone associated with extratropical cyclone.
What may we conclude about global tropospheric temperature trends?
Authors: Christy John R. , Norris William B.
Published: March 2004

Three realizations of the atmospheric temperature representing the layer from the surface to about 18 km generated from microwave emissions were published in 2003. Their 1979–2002 linear trends were stated as +0.24 ± 0.02, +0.12 ± 0.02 and +0.03 ± 0.05°C decade−1. Because the upper portion of this layer includes the stratosphere, the opportunity to utilize radiosonde measurements as an independent assessor of these trend values is diminished. However, the University of Alabama in Huntsville (UAH) also produces a lower tropospheric temperature (LT) product (0–8 km, trend of +0.08°C decade−1) for which radiosondes are much more suitable. Comparisons of this UAH product with radiosonde‐simulated layer temperatures show no significant difference in LT trends, lending support for the least positive trend of the three deeper layer values (+0.03 ± 0.05°C decade−1) as it was constructed in the same manner as LT.
Two‐dimensional structure of long‐period pulsations at polar latitudes in Antarctica
Authors: Yagova N. V. , Pilipenko V. A. , Lanzerotti L. J. , Engebretson M. J. , Rodger A. S. , Lepidi S. , Papitashvili V. O.
Published: March 2004

Two‐dimensional (2‐D) statistical distributions of spectral power and coherence of polar geomagnetic variations with quasi‐periods about 10 min are analyzed using data from magnetometer arrays in Antarctica. Examination of the 2‐D patterns of spectral power and coherence shows the occurrence of significant variations in geomagnetic power levels but with low spatial coherence near the cusp projection and in the auroral region. At the same time, low‐amplitude pulsations, which we coin Picap3 pulsations, are very coherent throughout the polar cap. The region occupied by coherent Picap3 pulsations is shifted toward local MLT night from the geomagnetic pole and is decoupled from the regions of auroral and cusp ULF activity. The spectral power varies with time at polar latitudes in a manner different from that at auroral latitudes. Diurnal variations of power at different stations at the same geomagnetic latitude exhibit different behavior depending on the station's position relative to geomagnetic and geographic poles. This asymmetry is shown to be partly attributed to the variations of the ionospheric conductance. The primary source of polar pulsations is probably related to intermittent magnetosheath turbulence and tail lobe oscillations, though a particular propagation mechanism has not as yet been identified.
Solar wind modulation of cusp particle signatures and their associated ionospheric flows
Authors: Rae I. J. , Fenrich F. R. , Lester M. , McWilliams K. A. , Scudder J. D.
Published: March 2004

This paper presents a multi‐instrument case study of the northern polar cusp at a variety of altitudes in conjunction with solar wind measurements. In the midaltitude cusp the Polar spacecraft observed pulsed particle and magnetic field signatures with periodicities ranging from ∼5 to 40 min for over 3 hours. Simultaneously, the CUTLASS HF radars measured poleward moving radar auroral forms (PMRAFs) with inter‐PMRAF periods similar to the Polar periodicities but several degrees of magnetic latitude poleward of the ionospheric footprint of the spacecraft. Such PMRAFs have previously been identified as ionospheric signatures of transient reconnection and flux transfer events. During this event, both the ACE and Wind spacecraft were making measurements in the solar wind. Oscillations in the time‐shifted solar wind magnetic fields and flows and calculated reconnection electric fields were observed with the same periodicities as those seen by Polar and CUTLASS. We conclude that the solar wind Alfvén waves modulate the dayside interaction, producing periodic flux transfer events resulting in the pulsed cusp particle signatures and PMRAFs. This study is the first observation of solar wind driven pulsed cusp particle signatures and associated PMRAFs, i.e., at both magnetospheric and ionospheric altitudes, at multiple simultaneous discrete periodicities.
Paleogene clockwise tectonic rotation of the Xining‐Lanzhou region, northeastern Tibetan Plateau
Authors: Dupont‐Nivet G. , Horton B. K. , Butler R. F. , Wang J. , Zhou J. , Waanders G. L.
Published: March 2004

To help understand the deformational history of the northeastern Tibetan Plateau, paleomagnetic samples were collected from 177 sites and two magnetostratigraphic sections at 16 localities distributed among Upper Jurassic‐Lower Cretaceous to Pliocene sedimentary and subordinate volcanic rocks within the Xining‐Lanzhou region (34–37°N, 101–105°E). A total of 127 sites at 12 localities yielded primary magnetizations confirmed by fold, reversal, and conglomerate tests. Age control on sedimentary rocks is provided by regional synthesis of chronostratigraphic data and our own biostratigraphic and magnetostratigraphic analysis presented in the companion paper by Horton et al. [2004]. Analysis of paleomagnetic declination combined with results from previous studies yield a remarkably consistent trend of vertical axis tectonic rotations across the studied region. Whereas 19.0 ± 7.2° to 37.8 ± 10.6° clockwise rotations are recorded consistently in all paleomagnetic localities in Lower Cretaceous to Eocene rocks, all paleomagnetic localities in Oligocene to Pliocene rocks have recorded minor to insignificant rotations, indicating that the Xining‐Lanzhou region has undergone a wholesale regional clockwise rotation during late Paleogene time. Consistent with regional chronostratigraphic and thermochronologic results, this late Paleogene tectonic rotation confirms that deformation reached regions of the northern Tibetan Plateau shortly after the initial collision of India with Asia. When compared to rotational paleomagnetic results from adjacent regions, several mechanisms can be proposed to explain the clockwise rotation. On the basis of consistency with geologic data we prefer a model involving clockwise rotation of the Xining‐Lanzhou region through right‐lateral shear, and associated shortening, related to northward indentation of the Qaidam basin.
Mesozoic‐Cenozoic evolution of the Xining‐Minhe and Dangchang basins, northeastern Tibetan Plateau: Magnetostratigraphic and biostratigraphic results
Authors: Horton B. K. , Dupont‐Nivet G. , Zhou J. , Waanders G. L. , Butler R. F. , Wang J.
Published: March 2004

Accurate stratigraphic ages are crucial to understanding the deformation history of the Tibetan Plateau prior to and during the Indo‐Asian collision. Efforts to quantify Mesozoic‐Cenozoic ages are hindered by limited fossils and a paucity of volcanic horizons and regionally correlative strata. Magnetostratigraphic and biostratigraphic results from the Xining‐Minhe‐Longzhong basin complex and Dangchang basin provide an improved chronology of nonmarine basin development over a large region of the northeastern Tibetan Plateau (34–37°N, 101–105°E). Analyses of 171 magnetostratigraphic levels and 24 palynological assemblages (>120 species) indicate Late Jurassic‐Early Cretaceous to mid‐Tertiary deposition. Although magnetic polarity zonation is incomplete, independent palynological age control partially restricts possible correlations to the Geomagnetic Polarity Timescale. The sediment accumulation record, basin provenance, structural geology, and published thermochronological data support a history of Jurassic exhumation, Late Jurassic‐Early Cretaceous fault‐related basin initiation, and Cretaceous‐Paleogene reduced accumulation. These patterns, which are compatible with Late Jurassic‐Early Cretaceous extension and Cretaceous‐Paleogene postrift thermal subsidence, were disrupted at about 40–30 Ma, when shortening related to the Indo‐Asian collision induced localized range uplift, vertical axis rotation, and amplified subsidence.
Direct measurements of bed stress under swash in the field
Authors: Conley Daniel C. , Griffin John G.
Published: March 2004

Utilizing flush mounted hot film anemometry, the bed stress under swash was measured directly in a field experiment conducted on Barret Beach, Fire Island, New York. The theory, development, and calibration of the instrument package are discussed, and results from the field experiment are presented. Examples of bed stress time series throughout a swash cycle are presented, and an ensemble averaged swash bed stress cycle is calculated. Strong asymmetry is observed between the uprush and backwash phases of the swash flow. The maximum bed shear stress exerted by the uprush is approximately double that of the backwash, while the duration of the backwash is 135% greater than that of the uprush. Friction coefficients in the swash zone are observed to be similar in magnitude to those from steady flow, with the mean observed friction coefficient equal to 0.0037. Swash friction coefficients derived from the current measurements exhibit a Reynolds number dependence similar to that observed for other flows. A systematic difference between coefficients for uprush and backwash is suggested.
Freshwater content variability in the Arctic Ocean
Authors: Häkkinen S. , Proshutinsky A.
Published: March 2004

Arctic Ocean model simulations have revealed that the Arctic Ocean has a basin‐wide oscillation with cyclonic and anticyclonic circulation anomalies (Arctic Ocean Oscillation (AOO)) that has a prominent decadal variability [Proshutinsky and Johnson, 1997]. This study explores how the simulated AOO affects the Arctic Ocean stratification and its relationship to the sea ice cover variations. The simulation uses the Princeton Ocean Model coupled to sea ice [Häkkinen and Mellor, 1992; Häkkinen, 1999]. The surface forcing is based on National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis and its climatology, of which the latter is used to force the model spin‐up phase. Our focus is to investigate the competition between ocean dynamics and ice formation/melt on the Arctic basin‐wide freshwater balance. We find that changes in the Atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main Arctic basin. The Atlantic water inflow anomalies are an essential part of AOO, which is the wind driven barotropic response to the Arctic Oscillation (AO). The baroclinic response to AO, such as Ekman pumping in the Beaufort Gyre, and ice melt/freeze anomalies in response to AO are less significant considering the whole Arctic freshwater balance.
Validation of HF radar probing of the vertical shear of surface currents by acoustic Doppler current profiler measurements
Authors: Ivonin Dmitry V. , Broche Pierre , Devenon Jean‐Luc , Shrira Victor I.
Published: March 2004

There exists no practical way of measuring vertical shear in the water just below the air/sea interface that contains information on air/water momentum fluxes. The paper is concerned with the validation of a recently proposed method of remote sensing of sea subsurface shear by means of a commonly used single‐frequency HF radar based on the use of the second‐order Bragg echo. To this end a dedicated field experiment was carried out off the French Mediterranean coast. In parallel with the HF radar probing, the independent simultaneous measurements of the subsurface shear profile were obtained by means of acoustic Doppler current profiler mounted on a floating platform, whose position was monitored by GPS. The comparison shows a fairly good agreement of the results (the discrepancy does not exceed 15%) and suggests a higher accuracy of the HF probing.
Seasonal salt budget of the northwestern tropical Atlantic Ocean along 38°W
Authors: Foltz Gregory R. , Grodsky Semyon A. , Carton James A. , McPhaden Michael J.
Published: March 2004

Strong seasonal river discharge, precipitation, evaporation, and the confluence of different water masses all contribute to a complex surface salinity seasonal cycle in the western tropical Atlantic. This paper addresses the atmospheric and oceanic causes of the seasonal variability in mixed layer salinity based on direct observations. Primary data sets include up to 5 years (September 1997 to December 2002) of measurements from moored buoys of the Pilot Research Array in the Tropical Atlantic (PIRATA), ship‐intake salinity observations, and near‐surface drifting buoys. We analyze the mixed layer salt balance at four PIRATA mooring locations along 38°W (15°N, 12°N, 8°N, and 4°N). This region is strongly influenced by seasonally varying precipitation associated with the latitudinal migrations of the Intertropical Convergence Zone. Thus at all four locations we find that surface freshwater fluxes are a major contributor to the mixed layer salt balance. We also find that horizontal transport plays a key role at most locations. At 15°N a strong seasonal cycle of horizontal advection contributes to a semiannual cycle of local storage. At 12°N the balance is mostly controlled by local surface freshwater fluxes, with a minor contribution from meridional advection. The strongest seasonal cycle of precipitation occurs at 8°N, resulting in a strong seasonal cycle of local salt storage. At 4°N the dominant semiannual cycle of precipitation is reflected in the surface freshwater flux. However, zonal and meridional advection are also significant, resulting in a strong annual variation in the mixed layer salt storage at this location. Some implications of our results for tropical Atlantic climate variability are briefly discussed.
Incorporating the effect of small‐scale circulations upon dust emission in an atmospheric general circulation model
Authors: Cakmur R. V. , Miller R. L. , Torres O.
Published: March 2004

Realistic simulation of dust emission in an atmospheric general circulation model (AGCM) is inhibited by the model's coarse resolution compared to the scale of the circulations observed to mobilize dust. We construct a probability distribution of wind speed within each grid box that depends upon the speed explicitly calculated by the AGCM and the magnitude of fluctuations about this speed. This magnitude is calculated by incorporating information from the AGCM's parameterizations of the planetary boundary layer along with dry and moist convection. Emission depends on the fraction of the wind speed distribution above the threshold value. As a consequence, emission can occur even if the explicitly resolved wind speed is less than the threshold, as long as the subgrid scale variability is large enough. In the AGCM, subgrid wind fluctuations are dominated by dry convection. This favors dust emission over deserts, where there is continuous mixing within the boundary layer due to intense solar heating of the surface. Particles emitted over arid regions are farther from precipitation and mixed higher above the surface by dry convection. This increases their wet and dry deposition lifetimes, respectively, increasing the aerosol load for a given emission. The AGCM's identification of “preferred meteorology” for emission by subgrid circulations complements the preferred sources of erodible particles included in other models. Given the introduction of subgrid variability, the AGCM's dust aerosol burden improves significantly, compared to the Total Ozone Mapping Spectrometer (TOMS) and advanced very high resolution radiometer (AVHRR) aerosol optical thickness (AOT) retrievals, over the Sahara, Sahel, and the Taklimakan as well as downwind of these regions, considered to be major sources of dust emission. This mechanistic representation of subgrid variability allows us to calculate the atmospheric burden of dust under different climates, where emission can change due to altered boundary layer variability in addition to changes in the mean wind speed.
Spatial correlation of permeability in cross‐stratified sediment with hierarchical architecture
Authors: Ritzi Robert W. , Dai Zhenxue , Dominic David F. , Rubin Yoram N.
Published: March 2004

Cross‐stratified deposits can give rise to a hierarchy of permeability modes, across scales, corresponding to a hierarchy of sedimentary unit types. The shape of the sample semivariogram for permeability can be largely controlled by the shape of the cross‐transition probabilities of unit types having the greatest contrast in permeability. The shape of those cross‐transition probabilities can be, in turn, largely determined by the variance of the lengths of those unit types. A sufficient condition for an exponential‐like semivariogram is the repeated occurrence of unit types having both a contrast in permeability and a large length variance. These relationships are shown through writing the identities for spatial correlation of permeability in a hierarchical and multimodal form and as a function of the transition probabilities for the sedimentary unit types. These relationships are also illustrated through analyzing data representing cross‐stratified sediments within a point bar deposit.
Soil mineralogy and slope effects on infiltration, interrill erosion, and slope factor
Authors: Ben‐Hur M. , Wakindiki I. I. C.
Published: March 2004

Interactions between the effects of soil mineralogy and of slope gradient on seal formation, infiltration rate (IR), runoff, and soil loss were evaluated, and the slope factor (Sf) functions for various soils with differing mineralogy were examined. Three different soils, on slopes of 9, 15, 20, and 25%, were subjected to 80 mm of simulated rainfall. The final IR was ≥20.5 mm h−1 in a clayey kaolinitic soil and ≤15 mm h−1 in smectitic soils. The total runoff, as a percentage of rainfall, ranged from 24 to 18%, 65 to 43%, and 50 to 35% from the kaolinitic, clayey smectitic, and sandy loam smectitic soils, respectively. The total soil loss ranged from 0.32 to 0.45 and from 1.14 to 3.93 kg m−2 for the kaolinitic and smectitic soils, respectively. In all three soils, increasing the slope gradient increased the detachment of coarse particles (>0.1 mm) more sharply than that of small particles (<0.1 mm), especially in the smectitic soils. Combining these results with previous findings for six soils indicated that soils could be divided into two groups according to their Sf values: (1) soils that contained smectite and were therefore dispersive and (2) soils that did not contain smectite and were therefore stable. For the former soils the regression Sf = 0.47exp(7.7 sin ) defined the Sf values significantly, whereas for the latter group a linear regression Sf = 0.81 + 1.77 (sin ) was required. It was suggested that the difference in the Sf functions was mainly due to seal formation enhancement by the smectite.
Experiments on upstream‐migrating erosional narrowing and widening of an incisional channel caused by dam removal
Authors: Cantelli Alessandro , Paola Chris , Parker Gary
Published: March 2004

The present paper reports on a laboratory investigation of the erosion of a deltaic front induced by the removal of a dam. We built a laboratory model of a dam, and observed both the sedimentation in the reservoir due to the downstream propagation of a delta front and the erosion of the delta front during dam removal, including measurement of channel morphology and flow field. The experiments provide a detailed view of a phenomenon that has not been described in detail to date: erosional narrowing. After the sudden removal of a dam, the flow incises into the reservoir deposit, first rapidly and then more slowly. During the initial period of rapid incision the width of the channel can in some circumstances undergo rapid and substantial narrowing, all the while incorporating sediment from its sidewalls. As the rate of incision slows, the channel first stops narrowing and then enters a phase of slow widening. This pattern of narrowing followed by widening tends to propagate upstream. The minimum channel width attained at a cross section, however, increases with upstream distance from the dam. While the period of erosional narrowing is very short, the incision is so intense that large amounts of sediment are delivered downstream in a short period of time. The process thus has practical implications in regard to the strategy of dam removal. Undistorted Froude similitude is used to scale the results up to field dimensions.
Setting up a virtual broadband seismograph network across Europe
Authors: van Eck Torild , Trabant Chad , Dost Bernard , Hanka Winfried , Giardini Domenico
Published: March 2004

European seismological observatories have undergone an impressive evolution in the last 5 to 10 years. The result is a very dense, but patch‐like coverage, with seismic instruments operated by a multitude of different observatories. Providing the research community with easy and rapid access to all of these waveform data poses a significant challenge. An ongoing European Community‐funded project, Mediterranean‐European Rapid Earthquake Data Information and Archiving Network (MEREDIAN), aims to shape these national efforts into a European‐Mediterranean infrastructure for broadband waveform data exchange and archiving.
Discovery of most distant object in the solar system
Authors: Showstack Randy
Published: March 2004

On 14 November 2003, Michael Brown, associate professor of planetary astronomy at the California Institute of Technology in Pasadena, California, was running a few minutes late for a class he teaches. He had planned to tell the students that there is nothing in the solar system beyond the Kuiper Belt, which he said has a strong outer edge at about 49 AU.

Instead, he cryptically told the students, “I am not sure this is true anymore.” That morning, he and several other members of his research team had discovered an orb no more than 1,700 km in diameter that currently is about 13 billion km—or about 90 AU— from the Sun. The planetoid, which the researchers have dubbed “Sedna” for the Inuit goddess of the ocean, is believed to be the most distant known object in our solar system from the Sun. Sedna's solar period is 10,500 years, and its most distant point from the Sun is 130 billion km.
NRC releases report on “Groundwater Fluxes across Interfaces”
Authors: Logan William S.
Published: March 2004

Estimates of groundwater recharge and discharge rates are needed at many different scales and for many different purposes. These include such diverse tasks as evaluating landslide risks, managing groundwater resources, locating nuclear waste repositories, and estimating global budgets of water and greenhouse gases. A report summarizing some of the major issues in recharge and discharge, titled “Ground‐water Fluxes across Interfaces,” has just been released by the Committee on Hydrologic Science (COHS) of the National Research Council. The report focuses on spatial and temporal variability of recharge and discharge, their scaling relationships in space and time, and interactions of groundwater with climate.
Comment on “Righting the balance: Gender diversity in the geosciences”
Authors: Herbert Floyd
Published: March 2004

To say that the fraction of geoscientists who are women is too small, as a recent Forum (Eos, 5 August 2003, p. 292) did, is mathematically equivalent to saying that the complementary set, male geoscientists, is too large. Does this mean that many of the male geoscientists should be eliminated?

A similar article in Science [Mervis, 2002] proposed that Title IX should be used in science as it was in college athletics, when a comparable quota requirement forced the elimination of a large fraction of the male athletes in order to reach a male/female ratio less than one.
Outstanding student paper awards
Authors: Anonymous
Published: March 2004

The following members in the Ocean Sciences Section and the Tectonophysics Section received Outstanding Student Paper Awards at the 2003 AGU Fall Meeting in San Francisco, California. (Winners in other sections will be announced in subsequent issues of Eos.)
Sea surface temperature fronts in the East (Japan) Sea and temporal variations
Authors: Park Kyung‐Ae , Chung Jong Yul , Kim Kuh
Published: April 2004

The spatial pattern of sea surface temperature(SST) fronts and its seasonality are presented for the entire East(Japan) Sea. They are based on semi‐monthly sea surface temperature(SST) gradient maps constructed from declouded SST images over the period 1990–1995. Fronts in the East Sea can be assigned to the Subpolar Front (SPF) in its central sea areas and to other fronts along the continental shelves. It is observed for the first time that the SPF, located mostly along about 40°N between 132.3°E and 138°E, bifurcates at both its eastern and western ends. The spatial structure of the SPF shows strong seasonality associated with: temporal variations of a warm eddy off the east coast of Korea; surface cooling due to Siberian cold air south of Vladivostok; and bifurcation of the Tsushima Warm Current west of the Tsugaru Strait. We have also observed an isolated frontal zone trapped by a seamount in the northeastern part of the Japan Basin.
Effect of Si on liquid Fe compressibility: Implications for sound velocity in core materials
Authors: Sanloup C. , Fiquet G. , Gregoryanz E. , Morard G. , Mezouar M.
Published: March 2004

Density of liquid Fe‐Si alloys was measured in situ up to 5 GPa‐1725 K by an X‐ray absorption technique using synchrotron radiation. Increasing the amount of silicon in liquid iron decreases the bulk incompressibility by only −0.5 GPa per 1 weight% of Si. These data confirm our previous prediction of a negligible effect of Si on liquid Fe bulk properties, prediction based on the observation of a similar local structure in liquid Fe and liquid Fe‐Si alloys. Si and S have therefore opposite effects on P‐waves velocity (vP = ), both elements reduce the bulk density of liquid iron but only S affects its compressibility. Since compression‐wave velocities in the Earth's outer core are slightly higher than in pure liquid Fe in the same P‐T conditions, it implies that Si would correct this discrepancy while S would increase it.
Determination of apparent quantum yield spectra of DMS photo‐degradation in an in situ iron‐induced Northeast Pacific Ocean bloom
Authors: Bouillon René‐Christian , Miller William L.
Published: March 2004

The wavelength dependence of the photochemical removal efficiency for DMS was studied for samples from an iron‐induced bloom in the Northeastern Pacific Ocean. In July 2002, a 64 km2 patch of ocean was iron‐fertilized near Ocean Station Papa (50°12′N; 144°45′W). Only small changes in pseudo‐first‐order apparent quantum yield (AQY*DMS(λ)) were observed outside the iron‐patch. However, inside the patch, AQY*DMS(λ) decreased considerably over the two weeks following the initial iron injection. A positive strong correlation was found between pseudo‐first‐order apparent quantum yield determined at 330 nm (AQY*DMS(330 nm)) and NO3− concentrations. We propose that NO3−‐photolysis has a substantial influence on DMS photo‐degradation rates in oceanic waters. This finding demonstrates that in addition to control DMS production, marine phytoplankton could indirectly influence the DMS photochemical loss rate via its control on NO3− distribution.
Degree‐2 harmonics of the Earth's mass load estimated from GPS and Earth rotation data
Authors: Gross Richard S. , Blewitt Geoffrey , Clarke Peter J. , Lavallée David
Published: March 2004

A fluid, mobile atmosphere and oceans surrounds the solid Earth and upon its land surface lays a continually changing distribution of ice, snow, and ground water. The changing distribution of mass associated with the motion of these surficial fluids changes the Earth's rotation by changing its inertia tensor and changes the Earth's shape by changing the load on the solid Earth. It has recently been demonstrated that large‐scale changes of the Earth's shape, and hence of the mass load causing the Earth's shape to change, can be measured using the global network of GPS receivers. Here, the degree‐2 mass load coefficients determined from GPS data are compared with those obtained from Earth orientation observations from which the effects of tides, winds, and currents have been removed. Good agreement is found between these two estimates of the degree‐2 mass load, particularly at seasonal frequencies.
Family history and risk of atopic dermatitis in children up to 4 years
Authors: Böhme M. , Wickman M. , Lennart Nordvall S. , Svartengren M. , Wahlgren C. F.
Published: April 2004

Background
The aetiology of atopic dermatitis (AD) is presumably multi‐factorial, with interactions between genetic and environmental factors.

Objective
To investigate the relation between atopic family history and development of AD up to 4 years.

Methods
Using annual questionnaires, we studied the cumulative incidence of AD in 0–4‐year‐olds in a prospective birth cohort of 4089. Atopic diseases in parents and siblings were recorded at birth. The occurrence of serum immunoglobulin E (IgE) antibodies to inhalant and food allergens was analysed in 2614 4‐year‐olds, and AD was divided into non‐IgE‐associated and IgE‐associated.

Results
Of the children without atopic parents, 27.1% developed AD; of those with single or double parental atopic history, 37.9% and 50.0%, respectively, did so. The effects of parental history of eczema and of atopic respiratory disease (ARD) did not differ significantly, nor did those of maternal and paternal history. Parental history of ARD increased the risk significantly more for IgE‐associated AD than for non‐IgE‐associated AD (odds ratio (OR) 2.0; 95% confidence interval (CI) 1.5–2.8 vs. OR 1.3; 95% CI 1.0–1.8), whereas the two forms lacked major differences in the effect of parental eczema. A history of eczema in older siblings was a risk indicator for both forms of AD (OR 2.1; 95% CI 1.4–3.3 vs. OR 1.8; 95% CI 1.2–2.6).

Conclusions
We found no difference between the effects of maternal and paternal atopic history. Parental eczema was a risk factor for AD irrespective of its association with IgE, but parental history of ARD mainly increased the risk of IgE‐associated AD.
AFLP analysis indicates no introgression of maize DNA in wheat x maize crosses
Authors: Brazauskas G. , Pasakinskiene I. , Jahoor A.
Published: April 2004

Amplified fragment length polymorphisms (AFLPs) were used to follow the possible introgression of maize DNA into haploids of wheat as a side‐effect of exploiting wheat x maize hybridization for haploid production. AFLPs were generated with 64 MseI/ EcoRI and 64 MseI/ PstI primer combinations, and the AFLP profiles of haploids were tested against those of maize and of the regular wheat varieties involved in the crosses. On average, 45.1 and 110.7 fragments were produced per assay with the MseI/EcoRI and MseI/PstI combinations, respectively. Different numbers of fragments were produced for wheat and maize: an average of 81 in the haploid, 80 in the wheat parent, and only 67.1 in maize. No evidence was found for introgression of maize into the wheat genome. Three unique AFLP fragments were detected in haploids, which were not present in the parental wheat genotypes. These ‘novel’ AFLP bands in the haploids could be caused by nucleo‐cytoplasmic interaction in the hybrid zygote. Such instability in the wheat genome is defined as temporal, as it was not detected in further generations when colchicine‐doubled progeny of the haploids was tested for the presence of polymorphic fragments.
Italian rice varieties: historical data, molecular markers and pedigrees to reveal their genetic relationships
Authors: Spada A. , Mantegazza R. , Biloni M. , Caporali E. , Sala F.
Published: April 2004

Two molecular marker approaches [amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR)] were employed to study genomic relationship among 96 rice cultivars. These included most of the best reputed Italian accessions. AFLP produced 461 fragments, 248 (53%) of which were polymorphic, SSR produced four to 11 alleles in the 12 genomic loci investigated. Genomic similarity was estimated independently for the two molecular marker techniques. Both AFLP and SSR dendrograms agree in splitting the cultivars into two main clusters: a small one, comprising four exotic accessions, and a larger one which could be split into four subgroups. These were also analysed on the basis of historical and pedigree information. This is the first report on the application of DNA polymorphism analysis to reveal genomic relationship among cultivated Italian rice germplasm. Results will be useful for breeding programmes.
The roles of vascular endothelial growth factor and angiopoietin‐2 in the regression of pregnancy pyogenic granuloma
Authors: Yuan K , Lin MT
Published: April 2004

Objectives:  The molecular mechanism for the regression of pregnancy pyogenic granuloma after parturition remains unclear. It has been proposed that, in the absence of vascular endothelial growth factor (VEGF), angiopoietin‐2 (Ang‐2) causes blood vessels to regress. Therefore, we investigated the roles of Ang‐2 and VEGF in the regression of pregnancy pyogenic granuloma.

Materials and methods:  The effects of tumor necrosis factor‐α (TNF‐α) on the transcription of Ang‐2 were tested in endothelial cells by reverse transcriptase‐polymerase chain reaction. A total of 15 specimens, including granulomas taken from five gravidas during pregnancy, five after parturition, and five from normal gingiva were compared by immunoblot assays for their relative expressions of Ang‐1, Ang‐2, Tie‐2, VEGF, and β‐actin. Double staining, immunohistochemistry for Ang‐2, and terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end‐labeling for apoptotic cells, were used to evaluate their regression. Finally, a fibrin gel culture system was used to investigate whether the withdrawal of VEGF and addition of Ang‐2 could cause newly grown microvessels to regress.

Results:  TNF‐α upregulated the expression of Ang‐2 in all endothelial cell types tested. The protein levels of Ang‐2 and Tie‐2 were highest in the granulomas in pregnancy, followed by those after parturition and normal gingiva, while Ang‐1 and β‐actin exhibited no significant differences. The amount of VEGF was high in the granulomas in pregnancy and almost undetectable after parturition. Double staining on granulomas after parturition revealed more apoptotic cells and less Ang‐2 than did those in pregnancy. In the fibrin gel assay, VEGF alone or in combination with Ang‐2 could protect microvessels from apoptosis, while Ang‐2 alone had no effect.

Conclusions:  Our findings suggest that a lack of VEGF is associated with apoptosis of endothelial cells and regression of granuloma. The roles of Ang‐2 require additional study.
Expression of caspase‐3 and structural changes associated with apoptotic cell death of keratinocytes in oral lichen planus
Authors: Tobón‐Arroyave SI , Villegas‐Acosta FA , Ruiz‐Restrepo SM , Vieco‐Durán B , Restrepo‐Misas M , Londoño‐López ML
Published: April 2004

Objective:  Apoptosis appears to be the mode of cell death by which damaged cells are removed from the lesional tissue. The aim of this study was to examine keratinocyte apoptosis and caspase‐3 (CPP32) expression in oral lichen planus (OLP).

Materials and methods:  Paraffin‐embedded samples of OLP (n = 30) and normal oral mucosa (NOM; n = 5) were prepared for haematoxylin–eosin (H & E), immunohistochemistry and electron microscopy. The number of apoptotic cells and the proportion of total cells that were either apoptotic (apoptotic index; AI) or mitotic (mitotic index; MI) were assessed in H & E stained sections. An immunostaining‐intensity‐distribution index (IIDI; proportion of stained cells × staining intensity) was used to assess CPP32 immunoreactivity.

Results:  Results showed a significant increase in the number of apoptotic cells in OLP (P < 0.001). In OLP, all apoptotic bodies were found in the basal and prickle epithelial layers. Compared with NOM, the AI was significantly greater in atrophic (P < 0.05), reticular (P < 0.001) and plaque‐like (P < 0.01) OLP. The MI was significantly greater in plaque‐like OLP (P < 0.01). The proportion of CPP32‐positive cells and the IIDI were significantly greater in all forms of OLP compared with NOM (P < 0.05). No difference in CPP32 expression was evident between clinical forms of OLP. Electron microscopy confirmed the light microscopic finding of apoptosis.

Conclusion:  Keratinocyte apoptosis and caspase‐3 expression co‐localized to the basal and parabasal epithelial layers, suggesting that proliferating epithelial cells may be targeted for destruction in OLP. Differences in epithelial AI and MI may underlie the various clinical and histological appearances of OLP.
Polarization switching induced by phase change in extremely short external cavity vertical-cavity surface-emitting lasers
Authors: Panajotov Krassimir , Arizaleta Mikel , Camarena Miren , Thienpont Hugo , Unold Heiko J. , Ostermann Johannes Michael , Michalzik Rainer
Published: April 2004

We experimentally investigate the spectral and polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to polarization insensitive optical feedback from an extremely short external cavity (few microns) and find that the wavelength and the current at which the light polarization switches between the two linearly polarized fundamental modes of the VCSEL are periodically modulated with the length of the external cavity. High contrast polarization switching is demonstrated for a quarter-wavelength change of the external cavity length. To explain our experimental findings we suggest a two-mode rate equation VCSEL model that considers the feedback optical field as instantaneous and accounts for multiple roundtrips in the external cavity with different coupling efficiencies back into the laser. Our numerical results are in very good agreement with the experiments.
Current transport mechanisms and their effects on the performances of InP-based double heterojunction bipolar transistors with different base structures
Authors: Jin Zhi , Prost W. , Neumann S. , Tegude F. J.
Published: April 2004

InP-based double heterojunction bipolar transistors (DHBTs) with different base structures were studied. The base structures are InGaAs with and without graded composition and GaAsSb. Both of the terminal currents of InP/GaAsSb/InP DHBT in forward and reverse modes are limited by the carrier transport across the base layer. This causes the offset voltage to be determined by the difference between the base-collector and base-emitter areas and by the normal common-base current gain. The emitter currents of both graded- and abrupt-base InP/InGaAs/InP DHBTs in the reverse mode are also limited by the carrier transport across the base layer, while their collector currents are limited by the band discontinuity of the base–emitter junction. The different current transport mechanisms of the terminal currents in the forward and reverse modes result in the larger offset voltage.
Relaxation of metallic Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk glass-forming supercooled liquid
Authors: Wen Ping , Zhao De Qian , Pan Ming Xiang , Wang Wei Hua , Huang Ya Ping , Guo Mei Li
Published: April 2004

The mechanical relaxation of metallic Zr46.75Ti8.25Cu7.5Ni10Be27.5 supercooled liquid has been measured by dynamic mechanical analysis. The relaxation behaviors are found to fit well the Kohlrausch–Williams–Watts equation in time domain as well as the Havriliak–Negami equation in frequency domain. Characteristic quantities relaxation time and time–temperature superposition are among the properties also exhibited. The metallic supercooled liquid is found to have common relaxation characteristics of the nonmetallic glass-forming supercooled liquids, demonstrating a connection of the underlying physics for quite different classes of glass formers.
Finite size effect of transmission property for metal hole arrays in subterahertz region
Authors: Miyamaru Fumiaki , Hangyo Masanori
Published: April 2004

The mechanism of the high band-pass transmission property of metal hole arrays (MHA), which is metal slabs perforated periodically with circular holes, in the subterahertz (sub-THz) wave region has been investigated. We measured the transmission spectra varying the number of holes using a THz time domain spectroscopy and observed that the peak transmittance normalized by the porosity of holes increases with increasing the number of holes. This finite size effect of the transmission characteristics of the MHA is attributed to the increase of the coupling efficiency between the incident THz wave and the surface mode excited on the MHA surface with increasing the number of holes.
Gap-gate field effect gas sensing device for chemical image generation
Authors: Filippini D. , Lundström I. , Uchida H.
Published: April 2004

A field effect chemically sensitive device, specially suited for the generation of scanning light pulse technique chemical images, is demonstrated. The present approach provides a complete separation between the required electrical biasing and chemical sensing functions inherently coupled in all previous systems. The concept is demonstrated by sensing hydrogen with insensitive biasing electrodes, composing a so-called gap gate, combined with discontinuous palladium clusters usually unsuitable for sensing in conventional arrangements. A simple one-dimensional model is used to explain the observed behavior.
Effects of electron concentration on the optical absorption edge of InN
Authors: Wu J. , Walukiewicz W. , Li S. X. , Armitage R. , Ho J. C. , Weber E. R. , Haller E. E. , Lu Hai , Schaff William J. , Barcz A. , Jakiela R.
Published: April 2004

InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films.
Hopping transport in TiO2:Co: A signature of multiphase behavior
Authors: Kennedy R. J. , Stampe P. A. , Hu Erhong , Xiong Peng , von Molnár Stephan , Xin Yan
Published: April 2004

TiO 2 : Co films have been grown in the rutile phase under varying oxygen growth pressures. Detailed microstructural analysis using transmission electron microscopy shows that reduced growth pressure increases the presence of cobalt clusters. The resistivity is found to follow a log(ρ)∼T−1/2 dependence over a wide temperature range. This behavior is characteristic of hopping transport in multiphase systems and implies the presence of cobalt clustering. Thus, transport measurements are shown to be sensitive to the appearance of metallic clusters in these systems and suggest a rapid method for determing the presence of clustering in these and other magnetically doped semiconductor systems.
Activation mechanism of annealed Mg-doped GaN in air
Authors: Lin Yow-Jon
Published: April 2004

In this study, the activation mechanism of annealed Mg-doped GaN in air and the influence of ambient on activation of Mg-doped GaN were investigated. According to the experimental results, we found that the dissociation of MgGa–H, and the formation of hydrogenated gallium vacancies (VGaH2) and gallium vacancies occupied by interstitial Mg during the air-activation process, led to an increase in the hole concentration. In addition, from the observed photoluminescence results and the secondary ion mass spectroscopy measurements, it is suggested that the formation of VGaH2 will result in an enhancement of hydrogen desorption from the MgGa–H complexes.
Blue GaN-based light-emitting diodes grown by molecular-beam epitaxy with external quantum efficiency greater than 1.5%
Authors: Waltereit P. , Sato H. , Poblenz C. , Green D. S. , Brown J. S. , McLaurin M. , Katona T. , DenBaars S. P. , Speck J. S. , Liang J.-H. , Kato M. , Tamura H. , Omori S. , Funaoka C.
Published: April 2004

We have grown blue (480 nm) nitride semiconductor light emitting diodes (LEDs) by plasma-assisted molecular beam epitaxy (MBE) on GaN templates. Packaged devices exhibited output powers up to 0.87 mW at 20 mA forward current. The corresponding external quantum efficiency was 1.68%. Utilizing a combination of direct current (dc) and pulsed electroluminescence measurements it has been demonstrated that at low (<20 mA) dc conditions the emission from these devices is governed by the combined effects of bandfilling and screening of electrostatic fields. However, at larger currents device heating dominates the emission properties.