bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase diagram for the constrained integer partitioning problem
Authors: Borgs C. , Chayes J. T. , Mertens S. , Pittel B.
Published: March 2004

We consider the problem of partitioning n integers into two subsets of given cardinalities such that the discrepancy, the absolute value of the difference of their sums, is minimized. The integers are i.i.d. random variables chosen uniformly from the set {1,…,M}. We study how the typical behavior of the optimal partition depends on n, M, and the bias s, the difference between the cardinalities of the two subsets in the partition. In particular, we rigorously establish this typical behavior as a function of the two parameters κ :=n−1log2M and b := |s|/n by proving the existence of three distinct “phases” in the κb‐plane, characterized by the value of the discrepancy and the number of optimal solutions: a “perfect phase” with exponentially many optimal solutions with discrepancy 0 or 1; a “hard phase” with minimal discrepancy of order Me−Θ(n); and a “sorted phase” with an unique optimal partition with discrepancy of order Mn, obtained by putting the (s + n)/2 smallest integers in one subset. Our phase diagram covers all but a relatively small region in the κb‐plane. We also show that the three phases can be alternatively characterized by the number of basis solutions of the associated linear programming problem, and by the fraction of these basis solutions whose ±1‐valued components form optimal integer partitions of the subproblem with the corresponding weights. We show in particular that this fraction is one in the sorted phase, and exponentially small in both the perfect and hard phases, and strictly exponentially smaller in the hard phase than in the perfect phase. Open problems are discussed, and numerical experiments are presented. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Effects of downsizing practices on the performance of hospitals
Authors: Chadwick Clint , Hunter Larry W. , Walston Stephen L.
Published: March 2004

Research has found that downsizing is not generally followed by improved organizational performance. Using a sample of hospitals that recently downsized, we evaluate the effects on performance of the human resource management (HRM) practices used in layoffs. Strategic HRM theory suggests that practices can have an impact on performance outcomes. We find that showing consideration for employees' morale and welfare during downsizing is positively related both to perceived success of downsizing and to financial performance following layoffs. Advance notice of layoffs is positively related to subsequent financial performance, but the provision of extended insurance to laid‐off employees is negatively related to financial performance. Planned redesign of work structures is positively related to perceived success, but has neutral to negative effects on financial performance. Copyright © 2004 John Wiley & Sons, Ltd.
Technology search investments: evolutionary, option reasoning, and option pricing approaches
Authors: Miller Kent D. , Arikan Andaç T.
Published: March 2004

How do firms allocate limited search resources among substituting technologies with uncertain prospects? This paper contrasts three different approaches. The first follows evolutionary theorists' portrayals of decision‐making processes under bounded rationality. The second approach—real option reasoning—fosters flexibility by investing in more than one technology and postponing the decision to specialize. Following the third approach—real option pricing—firms base their search investments on forward‐looking calculations of technology option prices. We lay out the contrasting theoretical assumptions behind each of these three approaches and construct a simulation model to compare their implications. Copyright © 2004 John Wiley & Sons, Ltd.
Intrauterine versus transvaginal sonography for benign and malignant disorders of the female reproductive tract
Authors: Gruessner S. E. M.
Published: March 2004

Objective

To determine the usefulness of high‐frequency intrauterine (IUS) vs. transvaginal (TVS) sonography in the evaluation of benign and malignant uterine and tubal abnormalities.

Methods

For IUS sonography, a high‐frequency (10–30 MHz) microtip probe with a maximum beam penetration depth of 126 mm was inserted intracervically; radial scanning (360°) was performed without cervical dilatation and without local or general anesthesia. For TVS, a 7.5‐MHz probe was used. The study population comprised 48 patients. Thirty‐three patients had gynecological diseases (cervical and endometrial cancer (n = 12), uterine leiomyomas (n = 10), sterility disorders (n = 11)); the remaining 15 patients served as a control group and had no gynecological diseases.

Results

IUS was accomplished in 45/48 (94%) patients. In contrast to TVS, preoperative staging by IUS—with assessment of depth of tumor invasion—concurred with the histopathological findings in all patients with cervical and endometrial cancer. The sonographic resolution of submucosal and intramural leiomyomas was superior with IUS vs. TVS. For patients with sterility disorders, intraluminal sonography of the Fallopian tubes was achieved in 64% of cases; endometrial nodules of the Fallopian tubes were depicted by intraluminal sonography (but not TVS).

Conclusions

IUS is superior to TVS in the evaluation of uterine and tubal abnormalities. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
The association between isolated fetal echogenic cardiac foci on second‐trimester ultrasound scan and trisomy 21 in low‐risk unselected women
Authors: Lamont R. F. , Havutcu E. , Salgia S. , Adinkra P. , Nicholl R.
Published: March 2004

Objectives

To determine the prevalence of and the association between trisomy 21 and isolated fetal echogenic cardiac foci (FECF) identified in the second trimester in an unselected low‐risk population.

Methods

All cases with isolated FECF were collected by reviewing the antenatal ultrasound database for 3 consecutive years. In order to include all trisomy 21 cases for the same period, the regional cytogenetics database and pediatric databases were examined. A 2 × 2‐table analysis was performed to establish the sensitivity, specificity and positive and negative predictive values of isolated FECF as a screening test for trisomy 21 in a low‐risk unselected population.

Results

In the 3‐year period of the study the total number of deliveries was 11 105, of which 10 769 (97%) had a routine detailed anomaly scan between 16 and 24 weeks' gestation. There were 311 cases (2.9%) of isolated FECF. Among these there was only one case (0.3%) of trisomy 21. In the same period, the total number of trisomy 21 cases was 14. Accordingly, the sensitivity of isolated FECF for detecting trisomy 21 was 7.1% and the specificity was 97.1%. Positive and negative predictive values of FECF were 0.3% and 99.9%, respectively.

Conclusion

In an otherwise healthy pregnancy, the finding of isolated FECF on a routine second‐trimester anomaly scan is normal and should not be considered as a risk factor for trisomy 21 in an unselected low‐risk population. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Ductus venosus blood flow assessment at 11 to 14 weeks of gestation and fetal outcome
Authors: Toyama J. M. , Brizot M. L. , Liao A. W. , Lopes L. M. , Nomura R. M. Y. , Saldanha F. A. T. , Zugaib M.
Published: March 2004

Objective

To evaluate the association between abnormal ductus venosus (DV) at 11–14 weeks' gestation and chromosomal abnormalities, structural defects and fetal outcome.

Methods

DV flow‐velocity waveform (DV‐FVW) and nuchal translucency thickness (NT) were prospectively evaluated in 1217 singleton pregnancies.

Results

The DV‐FVW was abnormal in 84 fetuses, NT was above the 95th centile in 160 fetuses and both markers were observed in 41 fetuses. Chromosomal defects were diagnosed in 22 fetuses. The sensitivity, specificity and positive and negative predictive values for an abnormal karyotype were 86.4%, 86.9%, 11.9% and 99.7%, respectively, for an increased NT. These values were 68.2%, 96.9%, 31.3% and 99.3%, respectively, for DV‐FVW abnormalities and 68.2%, 97.6%, 36.6% and 99.3%, respectively, when both markers were found simultaneously. Regarding structural defects, these values were 43.8%, 92.9%, 8.3% and 99.1% for an abnormal NT, 25.0%, 92.6%, 4.8% and 98.8% for DV‐FVW abnormalities and 25.0%, 97.9%, 15.4% and 98.9% for both together. Considering those cases of unexplained fetal demise, the values were 44.4%, 85.9%, 5.0% and 98.9% for NT abnormalities, 22.2%, 92.6%, 4.8% and 98.6% for an abnormal DV‐FVW and 22.2%, 98%, 15.4% and 98.7% for both. In cases with increased NT, the percentage of live births with normal karyotype and no major fetal structural defects decreased from 93.8% in normal DV‐FVW fetuses to 77.3% in abnormal ones.

Conclusion

DV assessment at 11–14 weeks' gestation is useful in screening for fetal chromosomal abnormalities and may help to reduce the false‐positive rate when combined with NT measurement. Abnormal DV‐FVW is also associated with an increase in adverse perinatal outcome in fetuses with enlarged NT. However, the value of DV‐FVW assessment in cases with normal NT is unclear. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Surface‐to‐tunnel seismic tomography studies at Yucca Mountain, Nevada
Authors: Gritto Roland , Korneev Valeri A. , Daley Thomas M. , Feighner Mark A. , Majer Ernest L. , Peterson John E.
Published: March 2004

A surface‐to‐tunnel seismic survey was conducted to estimate fracture intensity and distribution in the proposed nuclear waste repository area at Yucca Mountain, Nevada. A 5‐km‐long source line and a 3‐km‐long receiver line were located on top of Yucca Mountain ridge and inside the Exploratory Study Facility (ESF) tunnel, respectively. Numerical modeling showed that the first arrival P waves are mainly propagated in the repository horizon at depth. Therefore two‐dimensional travel time inversions were performed after the actual source locations on the ridge were projected onto the layer of interest at depth. Static corrections were applied to absorb the scatter in the new source locations and to correct for variations in source and receiver coupling and travel time shifts. Zero‐offset amplitude variations of the first arrivals across the receiver line inside the tunnel showed strong correlation with the fracture density determined by measurements along the tunnel wall. Wave guidance by subhorizontal fractures is suggested as a possible source for this phenomenon. Tomographic inversion of the travel time data revealed a low‐velocity zone in the south central area of the repository horizon. Conversion of the velocity tomography results to fracture‐density tomograms showed good correlation with fracture intensity mapped along tunnel walls. The fractured zone extends over a large area in the southern region of the potential repository, in particular, southwest of the intensely fractured zone encountered in the ESF tunnel. The rock in the northern section of the repository appears more competent compared to the highly fractured areas in the south.
A depth‐derived Pleistocene age model: Uncertainty estimates, sedimentation variability, and nonlinear climate change
Authors: Huybers Peter , Wunsch Carl
Published: March 2004

A new chronology of glaciation, spanning the last 780,000 years, is estimated from 21 marine sediment cores using depth as a proxy for time. To avoid biasing this “depth‐derived” age estimate, the depth scale is first corrected for the effects of sediment compaction. To provide age uncertainty estimates, the spatial and temporal variability of marine sediment accumulation rates are estimated and modeled as an autocorrelated stochastic process. Depth‐derived ages are estimated to be accurate to within ±9000 years, and within this uncertainty are consistent with the orbitally tuned age estimates. Nonetheless, the remaining differences between the depth and orbitally tuned chronologies produce important differences in the spectral domain. From the δ18O record, using the depth‐derived ages, we infer that there are weak nonlinearities involving the 100 kyr and obliquity frequency bands which generate interaction bands at sum and difference frequencies. If an orbitally tuned age model is instead applied, these interactions are suppressed, with the system appearing more nearly linear.
A detailed study of the polarity reversal mechanism in a numerical dynamo model
Authors: Wicht Johannes , Olson Peter
Published: March 2004

We analyze the mechanism of magnetic polarity reversals in a three‐ dimensional numerical dynamo model. A dynamo driven by compositional convection in a rotating spherical fluid shell with a solid, electrically conducting inner core exhibits regular reversals of its dominantly axial dipole magnetic field at Rayleigh number Ra = 300, Ekman number E = 0.01, Prandtl number Pr = 1 and Roberts number q = 20. The fluid motions that sustain the field include (1) azimuthal jets which generate toroidal magnetic field; (2) high‐latitude, helical convective plumes which generate poloidal magnetic field; and (3) meridional circulation which transports the magnetic field. Inverse poloidal field is produced locally in the convective plumes. Outcrops of reversed field create inverse magnetic flux spots on the core‐mantle boundary above the plumes that are precursors to the reversal. The dipole polarity change as seen from the surface occurs when the reversed magnetic flux is distributed over the core‐mantle boundary by the meridional circulation. In our model, the reversed flux is transported from south to north and the transitional field has a strong quadrupole component. The duration of the dipole transition is the meridional transport time, and corresponds to a few thousand years in the Earth's core. The duration of the stable polarity epochs depends on several effects, including the strengths of the sources of normal and reversed poloidal field in the plumes, flux transport, and flux diffusion. Comparable reversal periods are found in an equivalent kinematic dynamo model with steady velocities and without Lorentz forces, confirming that these reversals are not triggered by changes in the flow and are primarily magnetic induction effects.
Transient airglow enhancements observed from the space shuttle Columbia during the MEIDEX sprite campaign
Authors: Israelevich P. L. , Yair Y. , Devir A. D. , Joseph J. H. , Levin Z. , Mayo I. , Moalem M. , Price C. , Ziv B. , Sternlieb A.
Published: March 2004

First results of observations of ELVES during the last mission of the space shuttle Columbia by the MEIDEX (Mediterranean Israeli Dust Experiment) instrument are reported. During the eclipse parts of 25 orbits, there were observations toward the Earth's limb above the areas of active thunderstorms. Strong enhancements of the brightness of the airglow layer above lightning flashes were observed, with lateral dimensions exceeding 400 km. This phenomenon, known as ELVES, is a clear manifestation of the interaction between the electromagnetic pulse from the lightning stroke and the lower ionosphere. The observed ELVES have been produced both by vertical and horizontal discharges.
Tropospheric fate of Tunguska generated nitrogen oxides
Authors: Curci G. , Visconti G. , Jacob D. J. , Evans M. J.
Published: March 2004

We report on the production and transport of the 0.4 Tg of nitric oxide generated in the Siberian upper troposphere by the 1908 Tunguska object. The simulation uses a three‐dimensional chemistry and transport model of the global troposphere. We find that much of the nitric oxide forms nitric acid that deposits downwind of the blast site within the first month, with no severe damage to the ecosystem caused by acid rain. Ozone and OH are totally scavenged locally soon after the impact, then they increase respectively by up to 30% and 200% during the first weeks. The total deposition below the explosion is simulated within a factor of 2 of that indicated by an analysis of peat samples. Considering the details of the model this may be the first reasonable calculation on the acid deposition distribution, and could help in locating interesting sites for future peat samples collection.
Strong seismic reflections and melts in the mantle of a continental back‐arc basin
Authors: Stratford W. R. , Stern T. A.
Published: March 2004

A program of explosion seismology in central North Island, New Zealand, discovered a strong reflector within the upper mantle. Reflections from this (PmP2) are spatially confined to come from an interface 35 km deep and directly beneath a 40 km‐wide, back‐arc extension zone with active volcanism, high heat flow, low Pn wave‐speeds and thinned crust. On the basis of relative reflection amplitudes, the mantle reflections are most readily explained by an interface with a negative seismic impedance contrast. A satisfactory fit is obtained for a layer with a 40–90% drop in S‐wave speed (Vs) compared to the surrounding mantle. We interpret this layer to be a 40 km‐wide reservoir of partial melt pooled at a thermal boundary layer within the upper mantle.
Impact of short period, non‐tidal, temporal mass variability on GRACE gravity estimates
Authors: Thompson P. F. , Bettadpur S. V. , Tapley B. D.
Published: March 2004

Using orbital simulations of the Gravity Recovery and Climate Experiment (GRACE) spacecraft, we examined the effects on gravity recovery due to short period, non‐tidal temporal mass variability in the atmosphere, ocean, and continental hydrology. We found that the magnitude of the aliasing error was strongly correlated with the power of the high‐frequency variability of the models. Degree error relative to measurement error increased by a factor of ∼20 due to atmospheric aliasing (corresponding to geoid anomalies of approximately 1 mm at 500 km wavelengths), by a factor of ∼10 due to the ocean model, and by a factor of ∼3 due to the continental hydrology model. De‐aliasing done with approximate models gave the greatest reduction in aliasing error for the mid‐degrees and higher. For the atmosphere, the residual error was ∼1/5 times that of the aliasing error. A barotropic ocean model reduced the aliasing error due to a baroclinic model to nearly the level of measurement noise.
Space time distribution of afterslip following the 2003 Tokachi‐oki earthquake: Implications for variations in fault zone frictional properties
Authors: Miyazaki S. , Segall P. , Fukuda J. , Kato T.
Published: March 2004

GPS time series following the September 25, 2003 (UT) Tokachi‐oki earthquake (MW ∼ 8.0) reveal significant deformation. We use the Network Inversion Filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake. Afterslip is concentrated adjacent to the coseismic rupture zone, between the 2003 rupture and the inferred source regions of the 1968 Tokachi‐oki and the 1973 Nemuro‐oki earthquakes. The inversion shows a rapid decay of slip‐rate in the 2003 rupture zone, with slower deceleration in the surrounding regions. The stress‐velocity paths for the afterslip regions approximately follow dτ/d ln(v) ∼ 0.6 MPa, suggestive of steady‐state velocity strengthening friction. The complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties, although other interpretations can not be ruled out.
Large‐scale magnetic field inversions at sector boundaries
Authors: Crooker N. U. , Kahler S. W. , Larson D. E. , Lin R. P.
Published: March 2004

During the declining phase of the last solar cycle the Wind spacecraft observed a quasi‐recurrent pattern of mismatches between sector boundaries identified in suprathermal electron pitch angle spectrograms and in magnetic field data alone. Intervals of mismatch imply the presence of magnetic fields that are locally inverted or turned back on themselves in a way that is intrinsic to the sector boundary. We analyze eight cases of inversion during nine successive solar rotations in 1994–1995. These range in duration from 15 to 53 hours. In most the inversions are incomplete in a systematic way: Rather than pointing opposite to its true polarity along the Parker spiral, the magnetic field hovers at an orientation more nearly orthogonal to it, always in the sense of decreasing azimuth angle. The inversion pattern is consistent with passage through coronal streamer belt loops, in which the polarity of the two legs of each loop matches the sector structure and where one leg has been released from the Sun through interchange reconnection. There are four possible variations of this pattern, depending on the sense of polarity change across the sector boundary and on whether the leading or trailing leg has been released. The latter determines whether the sector boundary or the local field reversal passes first. Three of the four variations are represented in the eight cases. Plasma parameters in the inversions are typical of the slow wind. While some cases display signatures of interplanetary coronal mass ejections, many do not. Thus the inversions may represent the quiet, quasi‐steady end of a spectrum of large‐scale transient outflows.
Contribution of proton precipitation to space‐based auroral FUV observations
Authors: Galand M. , Lummerzheim D.
Published: March 2004

Imaging from space offers a unique way to access the global picture, and its temporal variability, of the particle energy input over the auroral ovals. Electron characteristics are inferred from the analysis of auroral images taken from space in two different spectral bands in UV or visible. Usually, only the electron component of the precipitation is considered, as most of the particle energy is carried by electrons. However, at some locations and certain times protons are a major energy source, that is, a major ionization and excitation source of the atmosphere. The response of POLAR/UVI, IMAGE/WIC and SI13, and TIMED/GUVI (used for retrieving the electron components) to proton precipitation is estimated. Secondary electrons produced within the proton beam also contribute to auroral emissions. Since they are less energetic than the secondary electrons produced in electron aurora, they have a different spectral signature. In addition, for a given energy flux, protons are usually more efficient at ionizing than electrons and yield larger values of the Pedersen ionospheric conductance. Therefore the difference between proton and electron aurora can lead to misinterpretation when brightness ratios are used to derive ionospheric conductances with parameterizations that are based on electron aurora. The validation and limitations of auroral analysis are discussed, especially at the equatorward edge of the afternoon oval, where protons are a significant energy source. In regions of >4 keV electron precipitation, the presence of proton precipitation, even modest (∼10%), yields a large underestimation of both the electron mean energy and the energy flux. Overall, the presence of proton precipitation yields a poor estimation of the electron mean energy. In proton‐dominated aurora, the Pedersen and Hall conductances are always underestimated with a large discrepancy for POLAR/UVI. However, in location where the protons are not dominant and the electron precipitation is not too hard, it is legitimate to estimate the particle characteristics and ionospheric conductances from the FUV brightnesses assuming pure electron precipitation. This is true in particular for the period around midnight (1900–0400 MLT), at a magnetic latitude of 65–67°.
Crust and upper mantle shear wave structure of the southwest United States: Implications for rifting and support for high elevation
Authors: West Michael , Ni James , Baldridge W. Scott , Wilson David , Aster Richard , Gao Wei , Grand Stephen
Published: March 2004

Surface wave phase velocities from 29 earthquakes are used to map the shear velocity structure to ∼350 km depth across the 950‐km‐long Rio Grande Rift Seismic Transect Experiment (LA RISTRA) seismic array in the southwest United States. Events from a range of back azimuths minimize the effects of multipathing. The resulting velocity model reveals a transition in lithospheric thickness from 200 km in the Great Plains to 45–55 km beneath the Rio Grande Rift, thickening beneath the Colorado Plateau to 120–150 km. The upper mantle low‐velocity signature of the rift is roughly twice the width of its surface morphology. An asthenospheric low‐velocity channel underlies the region west of the Great Plains and extends to 300 km depth. This channel is likely the result of warm mantle infill behind the sinking Farallon plate. Buoyant forces within this channel are sufficient to support much of the high elevation of the rift and plateau. No evidence for a deep mantle source is found beneath the rift, implying that present rifting is not driven by deep mantle upwelling. Velocities from 55 to 90 km beneath the rift axis are 10% slower than beneath the Great Plains, consistent with small amounts of partial melt. Low velocities extend to 200–300 km depth on either side of the rift but not directly beneath it, forming an inverted‐U shape. This feature may reflect mantle that has cooled through vertical advection in a subadiabatic environment. Upwelling may be reinforced by small‐scale convection caused by variations in lithospheric thickness and shallow mantle temperatures.
Effect of pressure on liquid‐liquid miscibility gaps: A case study of the systems CaO‐SiO2, MgO‐SiO2, and CaMgSi2O6‐SiO2
Authors: Hudon Pierre , Jung In‐Ho , Baker Don R.
Published: March 2004

In order to investigate the effects of liquid‐liquid phase separation on the igneous evolution of planetary bodies, we investigated immiscibility in the systems CaO‐SiO2, MgO‐SiO2, and CaMgSi2O6‐SiO2 at pressures to 1.5 GPa. Few changes are observed in the size of the miscibility gaps in these systems at 1.0 GPa. The decrease of the stable area of the gaps is mainly due to the increase of the monotectic temperature because the latter closely follows the melting temperature of SiO2 at high pressure. The pressure at which the whole CaO‐MgO‐SiO2 miscibility gap becomes metastable is estimated to be 1.81 GPa. The thermal and compositional extents of miscibility gaps associated with network‐modifier cations (such as Ca2+) do not change significantly with increasing pressure, but the extents are increased for amphoteric cations (such as Mg2+), and the change is more pronounced if the latter have small ionic radii and high ionic potentials. Cations possessing high crystal field stabilization energies produce the largest immiscibility fields at atmospheric pressure, and the passage from the high‐spin to the low‐spin state with increasing pressure is expected to yield even larger miscibility gaps. Magmas containing substantial amounts of amphoteric cations and cations with high crystal field stabilization energies are therefore potential candidates to develop immiscibility at high pressures.
Constitutive equations for ionic transport in porous shales
Authors: Revil A. , Leroy P.
Published: March 2004

The constitutive coupled equations describing ionic transport in a porous shale are obtained at the scale of a representative elementary volume by volume averaging the local Nernst‐Planck and Stokes equations. The final relationships check the Onsager reciprocity to the first order of perturbation of the state variables with respect to the thermostatic state. This state is characterized by a modified version of the Donnan equilibrium model, which accounts for the partition of the counterions between the Stern and diffuse Gouy‐Chapman layers. After upscaling the local equations the material properties entering the macroscopic constitutive equations are explicitly related to the porosity of the shale, its cation exchange capacity, and some textural properties such as the electrical cementation exponent entering Archie's law. This new model is then applied to predict the salt filtering and electrodiffusion efficiencies of a shale layer.
Electromagnetic field radiated by lightning to tall towers: Treatment of the discontinuity at the return stroke wave front
Authors: Pavanello D. , Rachidi F. , Rubinstein M. , Bermudez J. L. , Nucci C. A.
Published: March 2004

Recently, engineering return stroke models were extended to take into account the presence of an elevated strike object, which was modeled as an ideal uniform transmission line. We show in this paper that the current distribution associated with these extended models exhibits a discontinuity at the return stroke wave front, which cannot be considered to be physically plausible. This discontinuity arises from the fact that the current injected into the tower from its top is reflected back and forth at its ends and portions of it are transmitted into the channel; these transmitted pulses, which are supposed to travel at the speed of light, catch up with the return stroke wave front traveling at a lower speed, and no current is allowed to flow in the leader region above the front. This discontinuity needs to be carefully treated when calculating the radiated electromagnetic field through an additional term in the electromagnetic field equations, the so‐called “turn‐on” term. We additionally derive a general analytical formula describing the turn‐on term associated with this discontinuity for various engineering models. We present simulation results illustrating the effect of the turn‐on term on the radiated electric and magnetic fields for an elevated strike object of heighth= 168 m, corresponding to the Peissenberg tower in Germany. Finally, possible modifications to engineering models are suggested in order to eliminate this discontinuity.
Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Advanced Global Atmospheric Gases Experiment (AGAGE) observations at Cape Grim, Tasmania, and Mace Head, Ireland
Authors: O'Doherty S. , Cunnold D. M. , Manning A. , Miller B. R. , Wang R. H. J. , Krummel P. B. , Fraser P. J. , Simmonds P. G. , McCulloch A. , Weiss R. F. , Salameh P. , Porter L. W. , Prinn R. G. , Huang J. , Sturrock G. , Ryall D. , Derwent R. G. , Montzka S. A.
Published: March 2004

An update of in situ Advanced Global Atmospheric Gases Experiment (AGAGE) hydrofluorocarbon (HFC)/hydrochlorofluorocarbon (HCFC) measurements made at Mace Head, Ireland, and Cape Grim, Tasmania, from 1998 to 2002 are reported. HCFC‐142b, HCFC‐141b, HCFC‐22 and HFC‐134a show continued rapid growth in the atmosphere at mean rates of 1.1, 1.6, 6.0, and 3.4 ppt/year, respectively. Emissions inferred from measurements are compared to recent estimates from consumption data. Minor updates to the industry estimates of emissions are reported together with a discussion of how to best determine OH concentrations from these trace gas measurements. In addition, AGAGE measurements and derived emissions are compared to those deduced from NOAA‐Climate Monitoring and Diagnostics Laboratory flask measurements (which are mostly made at different locations). European emission estimates obtained from Mace Head pollution events using the Nuclear Accident Model (NAME) dispersion model and the best fit algorithm (known as simulated annealing) are presented as 3‐year rolling average emissions over Europe for the period 1999–2001. Finally, the measurements of HCFC‐141b, HCFC‐142b, and HCFC‐22 discussed in this paper have been combined with the Atmospheric Lifetime Experiment (ALE)/Global Atmospheric Gases Experiment (GAGE)/AGAGE measurements of CFC‐11, CFC‐12, CFC‐113, CCl4, and CH3CCl3 to produce the evolution of tropospheric chlorine loading.
A new 147–56 hPa water vapor product from the UARS Microwave Limb Sounder
Authors: Read W. G. , Wu D. L. , Waters J. W. , Pumphrey H. C.
Published: March 2004

Measurements of H2O in the tropopause region have been obtained by production of a new data set from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). A modified version of the retrieval scheme used to produce upper tropospheric humidity (UTH) from the MLS 203 GHz radiometer was applied to the MLS 183 GHz radiometer measurements to produce useful H2O data at 147, 121, 100, 83, 68, and 56 hPa. These new data, for the first 18 months of the UARS mission when the MLS 183 GHz radiometer was operational, fill an important “gap” around 100 hPa where previous MLS H2O data were generally not useful. Characteristics of the new data set are discussed and compared with National Oceanic and Atmospheric Administration (NOAA), Climate Monitoring and Diagnostics Laboratory (CMDL) frost‐point hygrometer, and UARS Halogen Occultation Experiment (HALOE) measurements.
Granular avalanches across irregular three‐dimensional terrain: 1. Theory and computation
Authors: Denlinger Roger P. , Iverson Richard M.
Published: March 2004

To establish a theoretical basis for predicting and interpreting the behavior of rapid mass movements on Earth's surface, we develop and test a new computational model for gravity‐driven motion of granular avalanches across irregular, three‐dimensional (3‐D) terrain. The principles embodied in the model are simple and few: continuum mass and momentum conservation and intergranular stress generation governed by Coulomb friction. However, significant challenges result from the necessity of satisfying these principles when deforming avalanches interact with steep and highly variable 3‐D terrain. We address these challenges in four ways. (1) We formulate depth‐averaged governing equations that are referenced to a rectangular Cartesian coordinate system (with z vertical) and that account explicitly for the effect of nonzero vertical accelerations on depth‐averaged mass and momentum fluxes and stress states. (2) We compute fluxes of mass and momentum across vertical cell boundaries using a high‐resolution finite volume method and Roe‐type Riemann solver. Our algorithm incorporates flux difference splitting, an entropy correction for the flux, and eigenvector decomposition to embed the effects of driving and resisting forces in Riemann solutions. (3) We use a finite element method and avalanche displacements predicted by Riemann solutions to compute Coulomb stresses conjugate to the displacements in 3‐D stress space. (4) We test the model output against analytical solutions, a sand cone conceptual experiment, and (in a companion paper) data from detailed laboratory experiments. Model results illustrate a complex interplay of basal traction and internal stress, and they successfully predict not only the gross behavior but also many details of avalanche motion from initiation to deposition.
EPA External Research Grants Program faces steep budget cuts
Authors: Showstack Randy
Published: March 2004

The Bush administration—s proposed budget cuts to the Environmental Protection Agency's research grants program, Science to Achieve Results (STAR),came under criticism at a hearing of the Science Subcommittee on Environment, Technology and Standards of the U.S. House of Representatives. The hearing was held 11 March.

Subcommittee members and several witnesses said that a proposed $36 million cut to the STAR'S fiscal year 2005 budget—compared to the FY2004 proposed budget—is too steep. They said the proposed $65‐million budget—which would be a cut of more than 30% from the previous fiscal year—would harm the program, as well as the agency's ability to receive outside research advice on a range of cutting‐edge environmental issues. Funding for STAR graduate fellowships also would be cut by $3.1 million, compared to the enacted level for FY2004.
Density‐Induced Plant Size Reduction and Size Inequalities in Ethylene‐Sensing and Ethylene‐Insensitive Tobacco
Authors: Pierik R. , Voesenek L. A. C. J. , de Kroon H. , Visser E. J. W.
Published: March 2004

Abstract: Plant competition for light is a commonly occurring phenomenon in natural and agricultural vegetations. It is typically size‐asymmetric, meaning that slightly larger individuals receive a disproportionate share of the light, leaving a limited amount of light for the initially smaller individuals. As a result, size inequalities of such stands increase with competition intensity. A plant's ability to respond morphologically to the presence of neighbour plants with enhanced shoot elongation, the so‐called shade avoidance response, acts against the development of size inequalities. This has been shown experimentally with transgenic plants that cannot sense neighbours and, therefore, show no shade avoidance responses. Stands of such transgenic plants showed a much stronger development of size inequalities at high plant densities than did wild type (WT) stands. However, the transgenic plants used in these experiments displayed severely hampered growth rates and virtually no response to neighbours. In order to more precisely study the impact of this phenotypic plasticity on size inequality development, experiments required plants that have normal growth rates and reduced, but not absent, shade avoidance responses. We made use of an ethylene‐insensitive, transgenic tobacco genotype (Tetr) that has wild type growth rates and moderately reduced shade avoidance responses to neighbours. Here, we show that the development of size inequalities in monocultures of these plants is not affected unambiguously different from wild type monocultures. Plots of Tetr plants developed higher inequalities for stem length than did WT, but monocultures of the two genotypes had identical CV (Coefficient of Variance) values for shoot biomass that increased with plant density. Therefore, even though reduced shade avoidance capacities led to the expected higher size inequalities for stem length, this does not necessarily lead to increased size inequalities for shoot biomass.
Senescence‐Related Gene Expression Profiles of Rosette Leaves of Arabidopsis thaliana: Leaf Age Versus Plant Age
Authors: Zentgraf U. , Jobst J. , Kolb D. , Rentsch D.
Published: March 2004

Abstract: Senescence is a form of programmed cell death (PCD) which leads to the death of whole organs, e.g., leaves or flowers, and eventually to the death of entire plants. Like all forms of PCD, senescence is a highly regulated and energy consuming process. Senescence parameters, like protein content, chlorophyll content, expression of photosynthesis‐associated genes or senescence‐associated genes (SAGs), reveal that senescence occurs in old leaves derived from young plants (6 week old) as well as in young leaves derived from older plants (8 week old), indicating that it is governed by the actual age of the leaves. In order to analyse the differential gene expression profiles during leaf senescence, hybridizations of high‐density genome arrays were performed with: i) individual leaves within the rosette of a 6‐week‐old plant and ii) leaves of the same position within the rosette but harvested from plants of different ages, ranging from 5 to 8 weeks. Cluster and genetree analyses, according to the expression pattern revealed that genes which are up‐regulated with respect to the age of the entire plant, showed completely different expression profiles with respect to the age of the individual leaves within one rosette. This was observed even though the actual difference in leaf age was approximately the same. This indicates that gene expression appears to be governed by different parameters: i) the age of the individual leaf and ii) the age and developmental stage of the entire plant.
The Effect of Seed Mass and Gap Size on Seed Fate of Tropical Rain Forest Tree Species in Guyana
Authors: van Ulft L. H.
Published: March 2004

Abstract: For eleven tree species, differing in seed mass, germination success (emergence success for two small‐seeded species) and the causes of failure to germinate were studied in the forest understorey and in logging gaps in the tropical rain forests of Guyana. In the forest understorey, germination success increased with seed mass. However, as gap size increased the difference between smaller and larger seeded species diminished because germination success of smaller‐seeded species increased slightly, while that of larger‐seeded species decreased dramatically. The negative effect of gap size on germination success of larger‐seeded species was caused by an increased risk of desiccation with gap size, which was a far more important seed mortality agent for larger than for smaller‐seeded species. Generally, seeds of smaller‐seeded species suffered more from insect predation and were removed at higher rates than larger‐seeded species. On the other hand, larger‐seeded species were eaten more by mammals than smaller‐seeded species. It is concluded that logging can result in shifts in the species composition in the tropical rain forests of Guyana which are dominated by species with large seeds, since germination success of larger‐seeded species is dramatically reduced in large logging gaps.
Calystegines inCalystegia sepiumdo not Inhibit Fungal Growth and Invertase Activity but Interact with Plant Invertase
Authors: Höke D. , Dräger B.
Published: March 2004

Abstract:Calystegines are alkaloidal glycosidase inhibitors. They accumulate predominantly in young and meristemic parts ofCalystegia sepium(Convolvulaceae).C. sepium,bindweed, infests meadows and cereal fields and is difficult to control chemically. Fungal pathogens againstC. sepiumare established as mycoherbicides.Stagonospora convolvuliLA39 attacksC. sepiumand does not affect crop plants, but young plants ofC. sepiumare less susceptible to the fungus. The interaction ofStagonospora convolvuliwith calystegines was investigated. Further, endophytic fungi of several classes were isolated from wild‐grownCalystegia sepiumleaves, and selected strains were tested for interaction with calystegines. Fungal growth on agar containing calystegines was not affected considerably. Plants in climate chambers were infected with an endophyte,Phomopsis,and with the fungal pathogen,Stagonospora convolvuli.Calystegine levels were measured in infected and non‐infected plant tissues. Accumulation depended on developmental stage of the plant tissue and was not influenced by infection. Acid invertase was measured from fungal mycelia and from infected and non‐infected plant tissues. Fungal acid invertase activity was not inhibited by 10 mM calystegine B2, while invertase fromC. sepiumleaves was inhibited. It is concluded that calystegines do not inhibit fungal development and sucrose consumption under the conditions of the present investigation, but may act by redirection of plant carbohydrate metabolism.
Gene Expression Analysis in Cucumber Leaves Primed by Root Colonization with Pseudomonas chlororaphis O6 upon Challenge‐Inoculation with Corynespora cassiicola
Authors: Kim M. S. , Kim Y. C. , Cho B. H.
Published: March 2004

Abstract: Root colonization by Pseudomonas chlororaphis O6, a non‐pathogenic rhizobacterium, induced systemic resistance in cucumber against target leaf spot caused by Corynespora cassiicola. A cDNA library was constructed using mRNA extracted from cucumber leaves 12 h after inoculation with C. cassiicola, using plants colonized by O6. To identify genes involved in O6‐mediated induced systemic resistance (ISR), we employed a subtractive hybridization method using mRNAs extracted from pathogen‐challenged cucumber leaves of plants lacking colonization. Differential screening of the cDNA library led to the isolation of six distinct genes encoding a GTP binding protein, a 60S ribosomal protein, a hypersensitive‐induced reaction protein, a ubiquitin extension protein, a pyridine nucleotide‐disulfide oxidoreductase, and a signal recognition particle receptor. Expression of these genes was not induced by O6 colonization alone. Rather, transcript accumulation of these genes increased significantly faster and stronger in the O6 colonized than in non‐colonized plants after challenge infection. Therefore, O6‐mediated ISR may be associated with an enhanced capacity for the rapid and effective activation of cellular defence responses after challenge inoculation.
Molecular Evolution of the S Locus Controlling Mating in the Brassicaceae
Authors: Fobis‐Loisy I. , Miege C. , Gaude T.
Published: March 2004

Abstract: Flowering plants possess self‐incompatibility (SI) mechanisms that promote outbreeding and thereby increase their genetic diversity. In the self‐incompatible Brassicaceae, recognition and rejection of self‐pollen is based on a receptor‐ligand interaction between male and female SI determinants. A transmembrane receptor kinase (S locus Receptor Kinase, SRK) determines the SI specificity in stigmatic cells, whereas a pollen coat‐localized ligand (S locus Cysteine‐Rich, SCR) determines the SI specificity in pollen. During recent years, major advances have been made in the understanding of the molecular basis of self‐pollen recognition by stigmatic cells. In this review, we will focus on evolutionary aspects of the SI system in Brassicaceae. We will describe how the study of the molecular aspect of SI, not only in the historical Brassica model but also in Arabidopsis species, has contributed to highlight certain aspects of evolution of SI in the Brassicaceae.
Changes in Activity of Energy Dissipating Mechanisms in Wheat Flag Leaves During Senescence
Authors: Dai J. , Gao H. , Dai Y. , Zou Q.
Published: March 2004

Abstract: Excitation energy dissipation, including the xanthophyll cycle, during senescence in wheat flag leaves grown in the field was investigated at midday and in the morning. With progress of senescence, photosynthesis (Pn) and actual PSII photochemical efficiency (ΦPSII) decreased markedly at midday. The decrease in extent of Pn was greater than that of ΦPSII. However, there was no significant decline in Pn and ΦPSII observed in the morning, except in leaves 60 days after anthesis. The kinetics of xanthophyll cycle activity, thermal dissipation (NPQ), and qf observed at midday during senescence exhibited two distinct phases. The first phase was characterized by an increase of xanthophyll cycle activity, NPQ, and qf during the first 45 days after anthesis. The second phase took place 45 days after anthesis, characterized by a dramatic decline in the above parameters. However, the qI, observed both at midday and in the morning, always increased along with senescence. A larger proportion of NPQ insensitive to DTT (an inhibitor of the de‐epoxidation of V to Z) was also observed in severely senescent leaves. In the morning, only severely senescent leaves showed higher xanthophyll cycle activity, NPQ, qf, and qI. It was demonstrated that, at the beginning of senescence or under low light, wheat leaves were able to dissipate excess light energy via NPQ, depending on the xanthophyll cycle. However, the xanthophyll cycle was insufficient to protect leaves against photodamage under high light, when leaves became severely senescent. The ratio of (Fj ‐ Fo)/(Fp ‐ Fo) increased gradually during the first 45 days after anthesis, but dramatically increased 45 days after anthesis. We propose that another photoprotection mechanism might exist around reaction centres, activated in severely senescent leaves to protect leaves from photodamage.
Molecular Cytogenetics of Xeranthemum L. and Related Genera (Asteraceae, Cardueae)
Authors: Garnatje T. , Vallès J. , Vilatersana R. , Garcia‐Jacas N. , Susanna A. , Siljak‐Yakovlev S.
Published: March 2004

Abstract: Seven representatives of the genera Amphoricarpus, Chardinia, Siebera, and Xeranthemum, all of them closely related as demonstraded by molecular phylogeny, have been studied from a cytogenetic perspective. Morphometrical karyotype parameters were calculated and idiograms obtained. Fluorochrome banding was performed with chromomycin A3 to identify GC‐rich regions in the chromosomes. Fluorescence in situ hybridization allowed us to locate the sites of 18S‐5.8S‐26S and 5S rDNA. Silver nitrate staining was used to count the number of nucleoli and to detect the active nucleolar organizing regions. Systematic and evolutionary issues are addressed in the light of these data.