bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuropsychological effects of treatments for adults with cancer: A meta-analysis and review of the literature
Authors: ANDERSON-HANLEY CAY , SHERMAN MARNE L. , RIGGS RAINE , AGOCHA V. BEDE , COMPAS BRUCE E.
Published: January 2004

A meta-analysis was conducted to evaluate possible neuropsychological effects of treatments for cancer in adults. A search revealed 30 studies, encompassing 29 eligible samples, and leading to inclusion of a total of 838 patients and control participants. A total of 173 effect sizes (Cohen'sd) were extracted across 7 cognitive domains and as assessed in the literature via 3 methods of comparison (post-treatment compared with normative data, controls, or baseline performance). Statistically significant negative effect sizes were found consistently across both normative and control methods of comparison for executive function, verbal memory, and motor function. The largest effects were for executive function and verbal memory normative comparisons (−.93 and −.91, respectively). When limiting the sample of studies in the analyses to only those with relatively “less severe” diagnoses and treatments, the effects remained. While these results point toward some specific cognitive effects of systemic cancer therapies in general, no clear clinical implications can yet be drawn from these results. More research is needed to clarify which treatments may produce cognitive decrements, the size of those effects, and their duration, while ruling out a wide variety of possible mediating or moderating variables. (JINS, 2003,9, 967–982.)
Caloric stimulation in neglect: Evaluation of response as a function of neglect type
Authors: ADAIR JOHN C. , NA DUK L. , SCHWARTZ RONALD L. , HEILMAN KENNETH M.
Published: January 2004

Contralesional neglect may be induced by either unawareness of contralesional stimuli (attentional neglect, AN) or failure to act in contralesional space (intentional neglect, IN). We examined whether contralesional cold caloric stimulation differentially affects ANversusIN. Patients with left-sided neglect (n= 16) from right-hemisphere lesions performed target cancellation and line bisection tasks. Using a video-based apparatus that reverses the right and left side of stimuli, patients with abnormal cancellation performance were divided into those with AN and those with IN. The 5 subjects with normal cancellation performance but rightward bisection bias were also separated into 2 neglect groups. Subjects performed cancellation or bisection tasks before and immediately after irrigation of the left auditory canal with ice water. Caloric stimulation induced brisk rightward nystagmus in all subjects. Subjects with AN cancelled more left-sided targets after stimulation than those with IN (p= .02). Whereas caloric stimulation significantly shifted bisection error leftward for both IN and AN groups (p< .0001), AN patients exhibited a greater magnitude of shift than the IN patients. While the basis for differential performance remains undefined, the data indicate that caloric stimulation influences AN more than IN. (JINS, 2003,9, 983–988.)
Intra-individual measures of association in neuropsychology: Inferential methods for comparing a single case with a control or normative sample
Authors: CRAWFORD JOHN R. , GARTHWAITE PAUL H. , HOWELL DAVID C. , VENNERI ANNALENA
Published: January 2004

Performance on some neuropsychological tests is best expressed as an intra-individual measure of association (such as a parametric or non-parametric correlation coefficient or the slope of a regression line). Examples of the use of intra-individual measures of association (IIMAs) include the quantification of performance on tests designed to assess temporal order memory or the accuracy of time estimation. The present paper presents methods for comparing a patient's performance with a control or normative sample when performance is expressed as an IIMA. The methods test if there is a significant difference between a patient's IIMA and those obtained from controls, yield an estimate of the abnormality of the patient's IIMA, and provide confidence limits on the level of abnormality. The methods can be used with normative or control samples of any size and will therefore be of particular relevance to single-case researchers. A method for comparing the difference between a patient's scores on two measures with the differences observed in controls is also described (one or both measures can be IIMAs). All the methods require only summary statistics (rather than the raw data from the normative or control sample); it is hoped that this feature will encourage the development of norms for tasks that use IIMAs to quantify performance. Worked examples of the statistical methods are provided using data from a clinical case and controls. A computer program (for PCs) that implements the methods is described and made available. (JINS, 2003,9, 989–1000.)
Syntactic language processing: ERP lesion data on the role of the
basal ganglia
Authors: KOTZ SONJA A. , FRISCH STEFAN , VON CRAMON D. YVES , FRIEDERICI ANGELA D.
Published: January 2004

The role of the basal ganglia in syntactic language processing was
investigated with event-related brain potentials in fourteen
neurologically impaired patients. Seven of these patients had basal
ganglia lesions while 7 other patients primarily had lesions of the
left temporo–parietal region excluding the basal ganglia. All
patients listened to sentences that were either correct or included a
verb argument structure violation. In previous experiments this type of
violation elicited a biphasic pattern of an N400–P600 complex in
young healthy participants. While the N400 may result from incorrect
semantic-thematic role assignment, the P600 reflects the fact that verb
information does not license the syntactic structure at present.
Results of the patient experiment revealed a double dissociation:
patients with left temporo–parietal lesions only show a P600,
whereas patients with lesions of the basal ganglia showed no P600, but
a negativity with extended duration that resembled an N400. The latter
pattern not only confirms previous reports that the basal ganglia
modulate the P600 but extends these results by showing that the N400 as
a late semantic–thematic integration process appears partially
modulated by the basal ganglia. (JINS, 2003, 9,
1053–1060.)
Left and right basal ganglia and frontal activity during language
generation: Contributions to lexical, semantic, and phonological
processes
Authors: CROSSON BRUCE , BENEFIELD HOPE , CATO M. ALLISON , SADEK JOSEPH R. , MOORE ANNA BACON , WIERENGA CHRISTINA E. , GOPINATH KAUNDINYA , SOLTYSIK DAVID , BAUER RUSSELL M. , AUERBACH EDWARD J. , GÖKÇAY DIDEM , LEONARD CHRISTIANA M. , BRIGGS RICHARD W.
Published: January 2004

fMRI was used to determine the frontal, basal ganglia, and thalamic
structures engaged by three facets of language generation: lexical
status of generated items, the use of semantic vs. phonological
information during language generation, and rate of generation. During
fMRI, 21 neurologically normal subjects performed four tasks:
generation of nonsense syllables given beginning and ending consonant
blends, generation of words given a rhyming word, generation of words
given a semantic category at a fast rate (matched to the rate of
nonsense syllable generation), and generation of words given a semantic
category at a slow rate (matched to the rate of generating of rhyming
words). Components of a left pre-SMA–dorsal caudate
nucleus–ventral anterior thalamic loop were active during word
generation from rhyming or category cues but not during nonsense
syllable generation. Findings indicate that this loop is involved in
retrieving words from pre-existing lexical stores. Relatively diffuse
activity in the right basal ganglia (caudate nucleus and putamen) also
was found during word-generation tasks but not during nonsense syllable
generation. Given the relative absence of right frontal activity during
the word generation tasks, we suggest that the right basal ganglia
activity serves to suppress right frontal activity, preventing right
frontal structures from interfering with language production. Current
findings establish roles for the left and the right basal ganglia in
word generation. Hypotheses are discussed for future research to help
refine our understanding of basal ganglia functions in language
generation. (JINS, 2003, 9, 1061–1077.)
Mental object rotation in Parkinson's disease
Authors: CRUCIAN GREGORY P. , BARRETT ANNA M. , BURKS DAVID W. , RIESTRA ALONSO R. , ROTH HEIDI L. , SCHWARTZ RONALD L. , TRIGGS WILLIAM J. , BOWERS DAWN , FRIEDMAN WILLIAM , GREER MELVIN , HEILMAN KENNETH M.
Published: January 2004

Deficits in visual-spatial ability can be associated with
Parkinson's disease (PD), and there are several possible reasons
for these deficits. Dysfunction in frontal–striatal and/or
frontal–parietal systems, associated with dopamine deficiency,
might disrupt cognitive processes either supporting (e.g., working
memory) or subserving visual-spatial computations. The goal of this
study was to assess visual–spatial orientation ability in
individuals with PD using the Mental Rotations Test (MRT), along with
other measures of cognitive function. Non-demented men with PD were
significantly less accurate on this test than matched control men. In
contrast, women with PD performed similarly to matched control women,
but both groups of women did not perform much better than chance.
Further, mental rotation accuracy in men correlated with their
executive skills involving mental processing and psychomotor speed. In
women with PD, however, mental rotation accuracy correlated negatively
with verbal memory, indicating that higher mental rotation performance
was associated with lower ability in verbal memory. These results
indicate that PD is associated with visual–spatial orientation
deficits in men. Women with PD and control women both performed poorly
on the MRT, possibly reflecting a floor effect. Although men and women
with PD appear to engage different cognitive processes in this task,
the reason for the sex difference remains to be elucidated.
(JINS, 2003, 9, 1078–1087.)
Neural basis for impaired time reproduction in Parkinson's
disease: An fMRI study
Authors: ELSINGER CATHERINE L. , RAO STEPHEN M. , ZIMBELMAN JANICE L. , REYNOLDS NORMAN C. , BLINDAUER KAREN A. , HOFFMANN RAYMOND G.
Published: January 2004

Studies involving brain-lesioned subjects have used the paced finger
tapping (PFT) task to investigate the neural systems that govern motor
timing. Patients with Parkinson's disease (PD), for example,
demonstrate abnormal performance on the PFT, characterized by decreased
accuracy and variability changes, suggesting that the basal ganglia may
play a critical role in motor timing. Consistent with this hypothesis,
an fMRI study of healthy participants demonstrated that the medial
frontostriatal circuit (dorsal putamen, ventrolateral thalamus, SMA)
correlated with explicit time-dependent components of the PFT task. In
the current fMRI study, PD patients and healthy age-matched controls
were imaged while performing the PFT. PD patients underwent 2 imaging
sessions, 1 on and the other off dopamine supplementation. Relative to
controls, PD patients were less accurate and showed greater variability
on the PFT task relative to controls. No PFT performance differences
were observed between the on and off medication states despite
significantly greater motor symptoms on the Unified Parkinson's
Disease Rating Scale (UPDRS) in the off medication state. Functional
imaging results demonstrated decreased activation within the
sensorimotor cortex (SMC), cerebellum, and medial premotor system in
the PD patients compared to controls. With dopamine replacement, an
increase in the spatial extent of activation was observed within the
SMC, SMA, and putamen in the PD patients. These results indicate that
impaired timing reproduction in PD patients is associated with reduced
brain activation within motor and medial premotor circuits. Despite a
lack of improvement in PFT performance, PD patient's brain
activation patterns were partially “normalized” with
dopamine supplementation. These findings could not be attributed to
greater head movement artifacts or basal ganglia atrophy within the PD
group. (JINS, 2003, 9, 1088–1098.)
Quantitative Convergent Beam Electron Diffraction Measurements of
Low-Order Structure Factors in Copper
Authors: Friis Jesper , Jiang Bin , Spence John C.H. , Holmestad Randi
Published: January 2004

Accurate low-order structure factors for copper metal have been
measured by quantitative convergent beam electron diffraction (QCBED).
The standard deviation of the measured structure factors is equal to or
smaller than the most accurate measurement by any other method,
including X-ray single crystal Pendellösung, Bragg γ-ray
diffraction, and high-energy electron diffraction. The electron
structure factor for the (440) reflection was used to determine the
Debye-Waller (DW) factor. The local heating of the specimen by the
electron beam is determined to be 5 K under the current illumination
conditions. The low-order structure factors for copper measured by
different methods are compared and discussed. The new data set is used
to test band theory and to obtain a charge density map. The charge
deformation map shows a charge surplus between the atoms and agrees
fairly well with the simple model of copper 2+ ions at the atomic sites
in a sea of free uniformly distributed electrons.
Analysis of Local Strain in Aluminum Interconnects by Convergent
Beam Electron Diffraction
Authors: Krämer Stephan , Volkert Cynthia A. , Mayer Joachim
Published: January 2004

Energy filtered convergent beam electron diffraction was used to
investigate localized strain in aluminum interconnects. By analyzing
the position of higher order Laue zone lines, it is possible to measure
the three-dimensional lattice strain with high accuracy
(∼10−4) and high spatial resolution (10 to 100 nm).
In the present article, important details of the strain analysis procedure
are outlined. Subsequently, results of measurements of the local variation
of thermal strains in narrow, free-standing interconnects are presented.
The strain development in single grains during thermal cycling between
−170°C and +100°C was measured in situ and local
stress variations along the interconnect were investigated. The interconnects
show reversible elastic behavior over the whole temperature range, leading to
large stresses at low temperatures. The strain state varies locally within
single grains, as well as from grain to grain, by as much as 50% in
both types of samples. By comparing the experimental findings with
elastic finite element modeling, a detailed understanding of the
triaxial strain state could be achieved.
Sufficient Conditions for Direct Methods with Swift Electrons
Authors: Marks L.D. , Sinkler W.
Published: January 2004

We investigate cases where one can argue that sufficient conditions
exist for Direct Methods to work with swift electrons. In addition to
simple cases where kinematical scattering holds (e.g., surfaces in plan
view), we identify three other configurations: (a) when 1s channeling
holds and kinematical scattering is statistically correct; (b) when
there is a mapping from kinematical to dynamical intensities that
preserves the order of the intensities, for instance with powder or
precession data, and (c) when the scattering is dominated by one type
of atom. We also briefly discuss the possibility of using Direct
Methods to restore the complex exit wave leaving a sample in the most
general case.
Quantitative Zone-Axis Convergent Beam Electron Diffraction:
Current Status and Future Prospects
Authors: Saunders Martin
Published: January 2004

Quantitative zone-axis convergent beam electron diffraction (CBED) is
now an established technique. Over the past decade it has been
developed into a tested method for the accurate refinement of structure
factors, allowing the details of the charge density and bonding effects
to be studied in crystalline materials. Strategies for obtaining the
most accurate results have evolved, and the most important influences
on the accuracy have been determined. Initial applications of the
technique to bond charge density determination have led to the
extension of the method to the refinement of other important parameters
influencing the experimental data, such as Debye–Waller factors
and the absorption potential. The development and current status of
quantitative zone-axis CBED are discussed. Prospects for the future
development and application of the technique are also considered.
Low-Dose, Low-Temperature Convergent-Beam Electron Diffraction and
Multiwavelength Analysis of Hydrocarbon Films by Electron
Diffraction
Authors: Wu Jinsong , Spence John C.H.
Published: January 2004

Aromatic hydrocarbon (perylene, coronene) and tetracontane films are
shown to produce useful convergent-beam electron diffraction (CBED)
patterns under low-dose and low-temperature conditions. These were
obtained using a Zeiss LEO-921 electron microscope with an omega energy
filter at liquid helium and nitrogen temperatures. The usefulness of
patterns showing CBED disks of constant intensity (“blank
disks,” indicating kinematic scattering) for structure analysis
is investigated, with the aim of avoiding film-bending artifacts. Using
CBED patterns from thicker areas, sample thickness was experimentally
determined using either two-beam or three-beam patterns. Koehler mode
illumination (a new form of SAD pattern offering smaller areas) was
also used, and the possibility of obtaining structure factor moduli
using the kinematic and two-beam approximations was investigated by
comparing measured diffraction intensities with experimental ones for
these known structures. The commonly used approximation
|F| ∼ Ig (intended
to account for bending) was found to be a worse approximation than the
two-beam approximation with well-defined excitation error for these
microdiffraction experiments. A new multiwavelength method of
retrieving structure factor moduli and thickness from microdiffraction
patterns using two-beam theory is demonstrated for tetracontane.
On the Consistency of QCBED Structure Factor Measurements for
TiO2 (Rutile)
Authors: Jiang Bin , Zuo Jian-Min , Friis Jesper , Spence John C.H.
Published: January 2004

The same Bragg reflection in TiO2 from 12 different (CBED)
patterns (from different crystals, orientations, and thicknesses) are
analyzed quantitatively to evaluate the consistency of the quantitative
CBED method for bond-charge mapping. The standard deviation in the
resulting distribution of derived X-ray structure factors is found to
be an order of magnitude smaller than that in conventional X-ray work,
and the standard error (0.026% for FX(110)) is slightly
better than obtained by the X-ray Pendellösung method applied to
silicon. This is sufficiently accurate to distinguish between atomic,
covalent, and ionic models of bonding. We describe the importance of
extracting experimental parameters from CCD camera characterization,
and of surface oxidation and crystal shape. The current experiments
show that the QCBED method is now a robust and powerful tool for
low-order structure factor measurement, which does not suffer from the
large extinction (multiple scattering) errors that occur in inorganic
X-ray crystallography, and may be applied to nanocrystals. Our results
will be used to understand the role of d-electrons in the chemical
bonding of TiO2.
Quantitative Electron Diffraction Evidence for One-Dimensional
Ordering in Magnetite above the Verwey Transition
Authors: Pacaud J. , Zuo J.M. , Hoier R. , Matsumura S.
Published: January 2004

Energy-filtered electron diffraction and three-dimensional reciprocal
lattice mapping was used to study the nature of diffuse scattering in
magnetite above the Verwey transition temperature. Characteristic Huang
scattering associated with a single molecular polaron is observed at
room temperature. As the temperature is lowered, the experiment shows
narrowing of diffuse scattering in the 〈001〉 directions and
additional ringlike diffuse scattering at q ∼ 0.8, which
suggests the presence of one-dimensional structures above the Verwey
transition. Experimental measurements of temperature-dependent
correlation lengths and diffuse scattering intensity indicate an
increase in the number and length of the one-dimensional structure as
the temperature is cooled toward the transition. This study
demonstrates the electron sensitivity to atomic displacement and the
quality of electron diffraction data for studying phase transition in
complex materials.
Seasonal ventilation of the cavity beneath Filchner‐Ronne Ice Shelf simulated with an isopycnic coordinate ocean model
Authors: Jenkins Adrian , Holland David M. , Nicholls Keith W. , Schröder Michael , Østerhus Svein
Published: January 2004

The ocean cavity beneath Filchner‐Ronne Ice Shelf is observed to respond to the seasonal cycle of water mass production on the continental shelf of the southern Weddell Sea. Here we use a numerical model to investigate the propagation of newly formed shelf waters into the cavity. We find that the model reproduces the most distinctive features of the observed seasonality and offers a plausible explanation for those features. The most saline shelf waters are produced in the far west, where the inflow to the cavity peaks twice each year. The major peak occurs during the short period around midwinter when convection reaches full depth and the densest waters are generated. Once the surface density starts to decline, dynamic adjustment of the restratified water column leads to a gradual fall in the salinity at depth and a secondary peak in the inflow that occurs in summer at the western coast. Beneath the ice shelf the arrival of the wintertime inflow at the instrumented sites is accompanied by a rapid warming, while the slower decline in the inflow leads to a more gradual cooling. Water brought in by the secondary, summer peak flows mainly to the eastern parts of the cavity. Here the seasonality is suppressed because the new inflows mix with older waters that recirculate within a topographic depression. This pooling of waters in the east, where the primary outflow of Ice Shelf Water is generated, dampens the impact of seasonality on the local production of Weddell Sea Bottom Water.
Relaxed eddy accumulation measurements of the sea‐to‐air transfer of dimethylsulfide over the northeastern Pacific
Authors: Zemmelink Hendrik J. , Gieskes Winfried W. C. , Klaassen Wim , Beukema Wim J. , de Groot Henk W. , de Baar Hein J. W. , Hintsa Eric J. , McGillis Wade R. , Dacey John W. H.
Published: January 2004

Gas transfer rates were determined from relaxed eddy accumulation (REA) measurements of the flux of dimethylsulfide (DMS) over the northeastern Pacific Ocean. This first application of the REA technique for the measurement of DMS fluxes over the open ocean produced estimates of the gas transfer rate that are on average higher than those calculated from commonly used parameterizations. The relationship between the total gas transfer rate and wind speed was found to be gas kgas = 0.53 (±0.05) U102. Because of the effect of the airside resistance, the waterside transfer rate was up to 16% higher than kgas. Removal of the airside transfer component from the total transfer rate resulted in a relation between wind speed and waterside transfer of k660 = 0.61 (±0.06) U102. However, DMS fluxes showed a high degree of scatter that could not readily be accounted for by wind speed and atmospheric stability. It has to be concluded that these measurements do not permit an accurate parameterization of gas transfer as a function of wind speed.
Sea‐to‐air fluxes from measurements of the atmospheric gradient of dimethylsulfide and comparison with simultaneous relaxed eddy accumulation measurements
Authors: Hintsa Eric J. , Dacey John W. H. , McGillis Wade R. , Edson James B. , Zappa Christopher J. , Zemmelink Hendrik J.
Published: January 2004

We measured vertical profiles of dimethylsulfide (DMS) in the atmospheric marine boundary layer from R/P FLIP during the 2000 FAIRS cruise. Applying Monin‐Obukhov similarity theory to the DMS gradients and simultaneous micrometeorological data, we calculated sea‐to‐air DMS fluxes for 34 profiles. From the fluxes and measured seawater DMS concentrations, we calculated the waterside gas transfer velocity, kw. Gas transfer velocities from the gradient flux approach are within the range of previous commonly used parameterizations of kw as a function of wind speed but are a factor of 2 smaller than simultaneous determinations of transfer velocity using the relaxed eddy accumulation technique. This is the first field comparison of these different techniques for measuring DMS flux from the ocean; the accuracy of the techniques and possible reasons for the discrepancy are discussed.
Kelvin wave signatures in stratospheric trace constituents
Authors: Mote Philip W. , Dunkerton Timothy J.
Published: February 2004

Connections, sometimes tenuous, have previously been noted between stratospheric Kelvin waves and several stratospheric trace constituents. The present study finds evidence of Kelvin wave signatures in ozone from the Microwave Limb Sounder (MLS) and Cryogenic Limb Array Etalon Spectrometer (CLAES) instruments aboard the Upper Atmosphere Research Satellite. Predominant variations near 10 days are associated with a Kelvin wave mode previously identified in MLS temperature. Variations in CLAES nitrous oxide also show some evidence of influence by this Kelvin mode. The results presented here show that the observing characteristics of the instrument can influence the derived structure and properties of Kelvin waves.
Global Assimilation of Ionospheric Measurements (GAIM)
Authors: Schunk Robert W. , Scherliess Ludger , Sojka Jan J. , Thompson Donald C. , Anderson David N. , Codrescu Mihail , Minter Cliff , Fuller‐Rowell Timothy J. , Heelis Roderick A. , Hairston Marc , Howe Bruce M.
Published: February 2004

The ionosphere is a highly dynamic medium that exhibits weather disturbances at all latitudes, longitudes, and altitudes, and these disturbances can have detrimental effects on both military and civilian systems. In an effort to mitigate the adverse effects, we are developing a physics‐based data assimilation model of the ionosphere and neutral atmosphere called the Global Assimilation of Ionospheric Measurements (GAIM). GAIM will use a physics‐based ionosphere‐plasmasphere model and a Kalman filter as a basis for assimilating a diverse set of real‐time (or near real‐time) measurements. Some of the data to be assimilated include in situ density measurements from satellites, ionosonde electron density profiles, occultation data, ground‐based GPS total electron contents (TECs), two‐dimensional ionospheric density distributions from tomography chains, and line‐of‐sight UV emissions from selected satellites. When completed, GAIM will provide specifications and forecasts on a spatial grid that can be global, regional, or local. The primary output of GAIM will be a continuous reconstruction of the three‐dimensional electron density distribution from 90 km to geosynchronous altitude (35,000 km). GAIM also outputs auxiliary parameters, including NmF2, hmF2, NmE, hmE, and slant and vertical TEC. Furthermore, GAIM provides global distributions for the ionospheric drivers (neutral winds and densities, magnetospheric and equatorial electric fields, and electron precipitation patterns). In its specification mode, GAIM yields quantitative estimates for the accuracy of the reconstructed ionospheric densities.
Mesoscale variability of sea surface pCO2: What does it respond to?
Authors: Mahadevan A. , Lévy M. , Mémery L.
Published: January 2004

We examine the impact of mesoscale and submesoscale oceanic processes on the distribution of sea surface pCO2 to explain variability observed at length scales of order 10 km. We ask whether the large pCO2 excursions (50–150 μ‐atm) that occur over 10–25 km of the sea surface could be induced by vertical advection associated with fronts and eddies in the pelagic ocean. A numerical model of a highly resolved, but idealized, mesoscale flow field is used to model the surface pCO2 response to submesoscale upwelling, taking into account the effect of wind, heat flux, and phytoplankton production. The effect of upwelled DIC on surface pCO2 is largely offset by the lower temperature of the upwelled water and the consumption of DIC by phytoplankton that respond to the simultaneously upwelled nitrate in a nutrient‐limited setting. Since an upwelling‐induced change in surface temperature, DIC, or nitrate is proportional to the vertical gradient of these properties beneath the mixed layer, the relative change in surface pCO2 is also dependent on the relative strengths of these gradients. We find that only small variations in surface pCO2 (∼10 μ‐atm) are induced by submesoscale upwelling. The larger (50–150 μ atm) variations observed at small scales (∼10 km) are therefore not a direct consequence of submesoscale upwelling. Our results suggest that these surface pCO2 differences are likely to have been generated at larger scales (by differential properties and levels of biological productivity) and cascaded to smaller scales by horizontal advection at the sea surface.
A new model for soil organic carbon turnover using bomb carbon
Authors: Hahn Volker , Buchmann Nina
Published: January 2004

A new model is presented that uses bomb carbon (14C enrichment) to calculate the turnover times of active soil organic carbon (SOC). The new approach overcomes major deficiencies of older models, particularly in respect to the 14C content of carbon input to SOC and of carbon output from SOC. Calculated turnover times of active carbon for ten European forest sites ranged from 4.0 to 15.1 years with a mean of 8.2 years. The model was successfully validated in soil incubation experiments, where the measured 14C content of (microbially) respired CO2 was on average 9.6% (ΔpM) higher than that of bulk SOC, but agreed considerably well with the modeled 14C content. Furthermore, we used the model's sensitivity tests to show that over long time periods (decades), soils can only sequester small amounts of carbon.
A hydrous melting and fractionation model for mid‐ocean ridge basalts: Application to the Mid‐Atlantic Ridge near the Azores
Authors: Asimow P. D. , Dixon J. E. , Langmuir C. H.
Published: January 2004

The major element, trace element, and isotopic composition of mid‐ocean ridge basalt glasses affected by the Azores hotspot are strongly correlated with H2O content of the glass. Distinguishing the relative importance of source chemistry and potential temperature in ridge‐hotspot interaction therefore requires a comprehensive model that accounts for the effect of H2O in the source on melting behavior and for the effect of H2O in primitive liquids on the fractionation path. We develop such a model by coupling the latest version of the MELTS algorithm to a model for partitioning of water among silicate melts and nominally anhydrous minerals. We find that much of the variation in all major oxides except TiO2 and a significant fraction of the crustal thickness anomaly at the Azores platform are explained by the combined effects on melting and fractionation of up to ∼700 ppm H2O in the source with only a small thermal anomaly, particularly if there is a small component of buoyantly driven active flow associated with the more H2O‐rich melting regimes. An on‐axis thermal anomaly of ∼35°C in potential temperature explains the full crustal thickness increase of ∼4 km approaching the Azores platform, whereas a ≥75°C thermal anomaly would be required in the absence of water or active flow. The polybaric hydrous melting and fractionation model allows us to solve for the TiO2, trace element and isotopic composition of the H2O‐rich component in a way that self‐consistently accounts for the changes in the melting and fractionation regimes resulting from enrichment, although the presence and concentration in the enriched component of elements more compatible than Dy cannot be resolved.
High precision Lu and Hf isotope analyses of both spiked and unspiked samples: A new approach
Authors: Lapen Thomas J. , Mahlen Nancy J. , Johnson Clark M. , Beard Brian L.
Published: February 2004

The functional form of instrumentally produced mass fractionation associated with MC‐ICP‐MS analysis is not accurately known and therefore cannot be fully corrected by traditional approaches of internal normalization using power, linear, or exponential mass‐bias laws. We present a method for robust correction of instrumentally produced mass‐fractionation of both spiked and unspiked samples that can be applied to mass analysis of Hf as well as Nd, Sr, Os, etc. Correction of 176Hf/177Hf for unspiked samples follows a traditional approach of internal normalization using an exponential law, followed by normalization to a standard of known composition, such as JMC‐475. For spiked samples, standards are used to characterize a linear instrumental mass‐bias coefficient; the mass‐bias coefficient is defined by the slope of a tie‐line between measured and true values of a standard. This approximation results in identical precision and accuracy of measurements for spiked and unspiked samples (±0.005% 2σ, external reproducibility). The effects of the spike on the 176Hf/177Hf ratio and calculation of the molar spike‐sample ratio is determined by a closed‐form solution modified from the double‐spike approach used for Fe isotope analysis by TIMS [Johnson and Beard, 1999]. The measured 176Lu/175Lu ratios are corrected by doping the sample with Er and using the 167Er/166Er ratio to externally normalize the 176Lu/175Lu ratio using an exponential law. Finally, spike‐sample equilibration is confirmed for our sample dissolution protocol through analysis of varying physical mixtures of 1 Ga garnet and hornblende, where all the data lie on a mixing‐line, within error, on a 176Lu/177Hf‐176Hf/177Hf diagram. Precision of 176Lu/177Hf ratios is determined to be ±0.2% (2σ) for standards and for physical mixtures of garnet and hornblende.
Stratospheric control of upward wave flux near the tropopause
Authors: Scott R. K. , Polvani L. M.
Published: January 2004

Using an idealized, global primitive equation model of the stratosphere‐troposphere system in which all tropospheric variability is surpressed, we demonstrate the existence of internal modes of stratospheric variability. The variability in our model is similar to that observed in the winter stratosphere, consisting of sudden‐warming like, wave‐driven decelerations of the polar vortex followed by a more gradual re‐establishment of the vortex by the radiative forcing. Using a common index of the strength of the stratospheric vortex, we find patterns of downward propagation resembling those found in recent observations. In addition, our model exhibits considerable variability in the upward flux of wave activity into the stratosphere; this variability strongly anti‐correlates with the index of the mid‐upper stratospheric vortex, again in agreement with recent observations.
Onset of turbulence induced by a Kelvin‐Helmholtz vortex
Authors: Matsumoto Yosuke , Hoshino Masahiro
Published: February 2004

A two‐dimensional MHD simulation of the Kelvin‐Helmholtz (K‐H) instability in a non‐uniform density medium shows a strong development of turbulence through non‐linear instabilities. The difference in density between the two media plays a crucial role on the fast turbulent mixing and transport. The onset of the turbulence is triggered not only by secondary K‐H instability but also by Rayleigh‐Taylor (R‐T) instability at the density interface inside the normal K‐H vortex, whose onset mechanisms are attributed to the centrifugal force of the rotating motion. The secondary R‐T instability alters the macroscopic structure by transporting dense fluids to tenuous region, while the secondary K‐H instability is just a seed for the turbulence. The onset mechanism and the formation of the broad mixing layer give a new understanding of the mixing process in a variety of geo‐ and astrophysical phenomena.
Transition to Turbulence in Shear above the Tropopause
Authors: Whiteway James A. , Klaassen Gary P. , Bradshaw Neil G. , Hacker Jorg
Published: January 2004

Airborne measurements were conducted above the UK during May and June 2000 in order to investigate turbulence and mixing in the tropopause region. Measurements of temperature frequently exhibited a periodic series of ramps that resembled a sawtooth pattern. These repeating structures were only observed in or near patches of intense shear‐generated turbulence associated with the jet‐stream. In each observed case the temperature ramps had the same orientation with respect to the wind shear. The temperature increased gradually in the direction of the shear, dropped suddenly, and the pattern repeated with wavelengths of about 1 to 1.2 km. Numerical simulation was applied to demonstrate that the observed temperature ramps are a signature of growing Kelvin‐Helmholtz waves that are just beginning to overturn in transition to turbulence. The fluctuations in wind became increasingly three‐dimensional along the direction of the shear with coherent oscillations that are consistent with the shear‐aligned vortices found in laboratory experiments and numerical simulations.
Heterogeneity and anisotropy of seismic attenuation in the inner core
Authors: Oreshin S. I. , Vinnik L. P.
Published: January 2004

We evaluate seismic attenuation in the inner core from the spectral ratio between the seismic phase PKP(DF) and either PKP(AB) or PKP(BC) at the epicentral distances from 150° to 170°. The global data set is divided into two groups according to the position of the turning point of PKP(DF) either in the eastern (from 50°E to 120°W) or the western hemisphere. In the eastern hemisphere the parameter t★ shows strong dependence on the epicentral distance and no dependence on the angle between the Earth's spin axis and PKP(DF) ray at the turning point. In the western hemisphere t★ is weakly dependent on the distance, and varies between approximately 0.7 s and 0.1 s for the angles between 0° and 90°, respectively. Our results allow us to reconcile seemingly incompatible results of many previous studies. The anisotropy of attenuation is correlated with the anisotropy of P velocity.
Three‐dimensional simulation on generation of polarization electric field in the midlatitude E‐region ionosphere
Authors: Yokoyama T. , Yamamoto M. , Fukao S. , Cosgrove R. B.
Published: January 2004

We have studied the generation of quasi‐periodic (QP) echoes and the associated polarization electric fields by using a fully three‐dimensional (3‐D) simulation. The 3‐D simulation is helpful to investigate realistic structures of the ionospheric plasma. Study of current closure system is one of the important issues and is suitable to be checked by our simulation. We simulated two particular cases: (1) the sporadic‐ E (Es) layer contains a plasma cloud which has finite zonal elongation and a southward neutral wind applied; and (2) the Es layer has a small sinusoidal perturbation and is at the equilibrium altitude within a rotational wind shear field. In case 1, Hall current driven by the polarization electric field flows within the plasma cloud and turns into the field‐aligned current that electromagnetically couples the E‐region and the F‐region. In case 2, on the other hand, current closure occurs mainly within the Es layer itself. We have found that integrated Pedersen conductivity of the F‐region () strongly affects the polarization mechanism in the E‐region. In case 2, when the Hall current driven by the polarization electric field can be closed within Es layers, smaller leads to larger polarization electric fields. In case 1, when the Hall current should flow as a field‐aligned current to the F‐region in order to sustain polarization electric fields, smaller leads to smaller polarization electric fields because serves as a resistance to the Hall current. Mapping of the electric field is also affected by . Our results suggest that coupling between the E‐region and the F‐region is not simply behaved but shows various behaviors depending on the E‐region condition.
Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike‐slip faults
Authors: Lin Jian , Stein Ross S.
Published: February 2004

We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface‐cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nuñez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust‐faulting events on the periphery of the seismic rupture and its downdip extension. These features are evident in aftershocks of the 1957 Mw = 9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw = 9.5 and 1995 Mw = 8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2–20 bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We also argue that slip on major strike‐slip systems modulates the stress acting on nearby thrust and strike‐slip faults. We calculate that the 1857 Mw = 7.9 Fort Tejon earthquake on the San Andreas fault and subsequent interseismic slip brought the Coalinga fault ∼1 bar closer to failure but inhibited failure elsewhere on the Coast Ranges thrust faults. The 1857 earthquake also promoted failure on the White Wolf reverse fault by 8 bars, which ruptured in the 1952 Mw = 7.3 Kern County shock but inhibited slip on the left‐lateral Garlock fault, which has not ruptured since 1857. We thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales.
Observations of swash zone velocities: A note on friction coefficients
Authors: Raubenheimer B. , Elgar Steve , Guza R. T.
Published: January 2004

Vertical flow structure and turbulent dissipation in the swash zone are estimated using cross‐shore fluid velocities observed on a low‐sloped, fine‐grained sandy beach [Raubenheimer, 2002] with two stacks of three current meters located about 2, 5, and 8 cm above the bed. The observations are consistent with an approximately logarithmic vertical decay of wave orbital velocities within 5 cm of the bed. The associated friction coefficients are similar in both the uprush and downrush, as in previous laboratory results. Turbulent dissipation rates estimated from velocity spectra increase with decreasing water depth from O(400 cm2/s3) in the inner surf zone to O(1000 cm2/s3) in the swash zone. Friction coefficients in the swash interior estimated with the logarithmic model and independently estimated by assuming that turbulent dissipation is balanced by production from vertical shear of the local mean flow and from wave breaking are between 0.02 and 0.06. These values are similar to the range of friction coefficients (0.02–0.05) recently estimated on impermeable, rough, nonerodible laboratory beaches and to the range of friction coefficients (0.01–0.03) previously estimated from field observations of the motion of the shoreward edge of the swash (run‐up).
Polar stratospheric clouds during SOLVE/THESEO: Comparison of lidar observations with in situ measurements
Authors: Brooks Sarah D. , Toon Owen B. , Tolbert Margaret A. , Baumgardner Darrel , Gandrud Bruce W. , Browell Edward V. , Flentje Harald , Wilson J. Charles
Published: January 2004

Polar stratospheric clouds (PSCs) were observed on several flights during the 1999/2000 SOLVE/THESEO mission. Here we present an analysis of PSC size distribution, composition, and particle phase based on near coincident measurements using the Multiangle Aerosol Spectrometer Probe (MASP) and Focused Cavity Aerosol Spectrometer (FCAS III) on board the ER‐2 as well as lidar instruments on board the DC‐8 and Falcon aircrafts. We calculate the aerosol backscatter ratios and aerosol depolarization ratios at infrared and visible wavelengths based on the particle size distributions measured by the MASP and FCAS III instruments. We then compare our calculations to observed lidar measurements taken from on board the DC‐8 and Falcon aircraft, which flew the same flight paths as the ER‐2 on 20 January and 3 February 2000, respectively. Our comparison shows that calculations based on the mixed clouds containing small (submicrometer) spherical particles and large (2.5–22 μm diameter) nonspherical particles seen by the FCAS III and MASP are consistent with lidar observations. Our analysis shows that the infrared aerosol depolarization ratio must be measured to detect and identify mixed PSC clouds and that relying only on measurements of depolarization in the visible causes incorrect identification of mixed clouds as solution droplets. This study suggests that mixed clouds of supercooled ternary solutions were observed in coexistence with larger solid nitric acid hydrate particles.