bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal balance and vertical pattern of photosynthetically active radiation within canopies of a tropical dry deciduous forest ecosystem in Mexico
Authors: Parker Geoffrey , Tinoco-Ojanguren Clara , Martínez-Yrízar Angelina , Maass Manuel
Published: May 2005

Major components of the flux density of global photosynthetically active radiation (PAR) were measured above and within canopies in a tropical deciduous forest on the Pacific coast of Mexico. At each of 69 locations grouped along a topographic sequence the PAR reflected from the top of the canopy, the vertical profile of transmittance, and the reflectance from the ground, were measured as many as four times in the year, including the extremes of the wet and dry seasons. With these observations an annual balance of the portion of PAR radiation reflected and absorbed by the canopy and ground was assembled and the detailed spatial and temporal dynamics of PAR within canopy layers were estimated. Canopy stature declined along the topographic sequence and the shape of the transmittance profiles reflected this. In locations of declining moisture availability the fraction of PAR absorbed by the ground increased and the fraction absorbed by non-foliar tissues decreased. Seasonal variation in canopy structure was the dominant influence on the partitioning of radiation – spatial variation was less important. Of a total annual PAR input of 15 200 mol m−2, about 95% of incident PAR was absorbed, 50% by leaves, 25% by non-foliar tissues and 20% by the ground. The remaining 5% was reflected by the top of the canopy.
Reproductive size thresholds in tropical trees: variation among individuals, species and forests
Authors: Wright S. Joseph , Jaramillo M. Alejandra , Pavon Javier , Condit Richard , Hubbell Stephen P. , Foster Robin B.
Published: May 2005

Relative size at onset of maturity (RSOM) is defined as size at first reproduction divided by asymptotic maximal size. RSOM is remarkably constant among species within many higher clades of animals, but varies widely among tree species from the Pasoh Forest Reserve, Malaysia according to the work of S. C. Thomas. RSOM was examined for 16 mid-storey and canopy tree species from a second tropical forest at Barro Colorado Island (BCI), Panama. Interspecific variation in RSOM was equally large for BCI and Pasoh and was unrelated to gap dependence or life form for BCI species. The shape of the relationship between size and the proportion of individuals that were reproductive differed between forests, with an abrupt increase over a narrow range of sizes at Pasoh and a more gradual increase over a wider range of sizes at BCI. Both overtopping trees and heavy liana infestation reduced the probability that BCI trees were reproductive. This presumably reflects reduced availability of carbon for reproduction. We speculate that greater liana loads and a greater abundance of large, shade-casting trees at BCI may increase variation among individuals and contribute to the relatively wide range of sizes characterized by a mixture of sterile and fertile individuals observed for most BCI species.
Vertical stratification of leaf-beetle assemblages (Coleoptera: Chrysomelidae) in two forest types in Panama
Authors: Charles Elroy , Basset Yves
Published: May 2005

To study vertical gradients of arthropod species richness in tropical forests, adult chrysomelids were surveyed with similar sampling effort by beating in four plots of 0.8 ha, representative of the canopy and understorey of one wet and one dry forest in Panama. Samples included in total 4615 individuals representing 253 species, and were of similar species richness at the two study sites. At both sites, chrysomelids were significantly more species-rich in the canopy than in the understorey. The proportion of species shared between the two study sites was 24%, whereas 16% and 28% of species were shared between the canopy and understorey of the wet and dry sites, respectively. Mature trees supported more and different chrysomelid species than conspecific saplings. A higher proportion of liana feeders vs. tree feeders occurred at the dry site than at the wet site. Multivariate analyses confirmed the faunal differences between the wet and dry sites and that stratification was more marked at the wet site than at the dry site. The latter observation may relate to differences in forest physiognomy (a tall and closed canopy at the wet site) and to the high interconnectivity via lianas between the understorey and canopy at the dry site.
A comparison of methods for determining soil water availability in two sites in Panama with similar rainfall but distinct tree communities
Authors: Kursar Thomas A. , Engelbrecht Bettina M. J. , Tyree Melvin T.
Published: May 2005

Plant productivity, distribution and diversity in tropical rain forests correlate with water availability. Water availability is determined by rainfall and also by the available water capacity of the soil. However, while rainfall is recognized as important, linkages between plant distribution and differences among soils in available water capacity have not been demonstrated. One reason for this may be that measurements of soil moisture, such as gravimetric water content, may be overly simplistic. To investigate this, we compared two sites in Panama, Allee and Rio Paja, which have similar rainfall but different plant communities. Soil water release curves were obtained from about −0.1 MPa to −9 MPa, permitting us to calculate available water capacity. The Rio Paja site had 17% greater available water capacity (between −0.1 MPa to −3 MPa), whereas the gravimetric water content at Rio Paja was lower by 16% in rainy season and by 41% at the end of the dry season. Hence soil gravimetric water content and soil available water capacity did not correspond. The results suggest that available water capacity may better predict plant distributions. Hence, whenever possible, available water capacity should be determined in addition to gravimetric water content.
Ocelot (Felis pardalis) population densities, activity, and ranging behaviour in the dry forests of eastern Bolivia: data from camera trapping
Authors: Maffei Leonardo , Noss Andrew J. , Cuéllar Erika , Rumiz Damián I.
Published: May 2005

In comparison with the Neotropical big cats, jaguar (Panthera onca L.) and puma (Felis concolor L.), medium and small felids are poorly studied. Furthermore, studying wild felids in forest habitats is extremely difficult using direct methods given that most species are principally nocturnal and secretive (Gittleman 1996). Indirect methods are therefore particularly important, e.g. radio-telemetry (Emmons 1987, 1988; Konecny 1989, Ludlow & Sunquist 1987) or camera trapping (Maffei et al. 2002, Trolle & Kéry 2003). Using systematic camera trap surveys, we compare the population density of ocelots (Felis pardalis L.) across five Bolivian dry-forest sites with different habitat types and/or annual rainfall regimes (Table 1). We hypothesize that ocelot densities will decline as rainfall declines. In addition, we estimate the population of ocelots in the 34 400-km2 Kaa-Iya del Gran Chaco National Park. Finally, we describe and evaluate additional ecological information provided by camera trapping: activity patterns relative to seasonality and moon phase, sex ratios, ranging patterns and relative abundance compared with sympatric felids.
Rapid evolution of magnetic decreases (MDs) and discontinuities in the solar wind: ACE and Cluster
Authors: Tsurutani Bruce T. , Guarnieri Fernando L. , Lakhina Gurbax S. , Hada Tohru
Published: May 2005

An experiment was conducted to identify and measure the same magnetic decreases (MDs) and interplanetary discontinuities at two different points in space separated by ∼0.01 AU along the radial distance from the sun. The ACE and Cluster satellite data were used in this study. Solar wind speeds measured at Cluster were used to calculate the approximate (earlier) times of arrival at ACE. The field component changes at both spacecraft were intercompared to ensure that the same discontinuities were detected. Out of 7 MDs/discontinuities selected, 6 were identified at ACE. The MDs/discontinuities were identified within 7 s to 35 s of the convection times. The MD thicknesses at Cluster were substantially smaller than at ACE. The ratio of thicknesses varied from 0.21 to 0.045. One possible interpretation of this observation is that the Alfvén wave front (rotational discontinuity) is steepening by a factor of greater than 15 per wavelength propagated. This may have important consequences for the generation of high frequency turbulence in interplanetary space. It is noted that the 6 discontinuities transited the ∼0.01 AU distance from ACE to Cluster with essentially the solar wind convection speed. A possible mechanism contributing to this feature is discussed.
Stagnant exterior cusp region as viewed by energetic electrons and ions: A statistical study using Cluster Research with Adaptive Particle Imaging Detectors (RAPID) data
Authors: Zhang H. , Fritz T. A. , Zong Q.‐G. , Daly P. W.
Published: May 2005

We present statistical results based on the data set obtained by Cluster when these spacecraft were in the dayside cusp and magnetopause. Forty clearest stagnant exterior cusp (SEC) events have been selected from ∼150 cusp crossings from 1 January to 30 April 2001 and from 1 March to 30 April 2002. The identification of the SECs was made on the basis of the following criteria: high‐density plasma (comparable to the sheath level) and small or stagnant plasma flow (Vx < 60 km s−1). We found that energetic ions are observed in the high‐latitude magnetospheric region for 32 SEC crossings (80%) and energetic electrons are observed on 9 of 40 events (22.5%). The SEC is found to lie predominantly within 1000–1300 magnetic local time (MLT); however, there are some cases where this region extends to both earlier and later MLTs. Twenty‐nine SEC events (72.5%) have been found in association with depressed magnetic field. The angular difference between the interplanetary magnetic field (IMF) and local clock angles is a good criterion for 29 SEC events (72.5%). The particle spectra are characterized by a power law, and the power law index is found to be closely related to solar wind velocity. The spectra seem to be harder for higher solar wind velocity. We also found that the higher the solar wind velocity, the higher the ion flux in the SEC region. The magnetic shear angle is the difference between local B vector and IMF clock angle projected on the plane perpendicular to the shock normal. The larger the magnetic shear angle, the more turbulent the magnetic field in the SEC. The turbulence in the SEC region does not affect the power law index, but it is one of the factors controlling of the SEC region. Further, there is no clear relationship found between the power law index and IMF Bz, Dst, or the magnetic shear angle.
Numerical modeling of electron energy‐time dispersions in the high‐latitude part of the cusp region
Authors: Tanaka H. , Saito Y. , Asamura K. , Mukai T.
Published: May 2005

We have constructed a one‐dimensional numerical model of electron acceleration with dispersive Alfvén waves using realistic parameters based on a rocket observation in the high‐latitude part of the cusp region. This paper demonstrates that our model could quantitatively reproduce important characteristics of observed electron energy‐time dispersions, such as their fluxes, energy range, pitch angle distribution, and source altitudes. The energy‐time dispersion at the rocket altitude is produced by a time‐of‐flight effect of magnetosheath‐originated electrons accelerated by the resonant interaction with inertial Alfvén waves (IAWs) at altitudes of 2000 ∼ 6000 km. The higher‐energy electrons are generated at higher altitudes. The energy‐time dispersion changes according to three key parameters: wave power, perpendicular wavelength, and wave frequency. The wave power affects the flux and the maximum electron energy, and the perpendicular wavelength affects the source altitude calculated by the time‐of‐flight analysis, while the wave frequency (time period) affects the time width of the energy‐time dispersion. We summarize a reasonable set of these parameters for a typical energy‐time dispersion observed in the cusp/cleft region. Finally, we suggest that the IAWs are generated at the dayside magnetopause in association with magnetic reconnection and then propagate toward the ionosphere along the open field line connected to the magnetosheath. Their resonant acceleration of local electrons injected from the magnetosheath at altitudes of several thousand kilometers is the cause for multiple electron energy‐time dispersions observed in the high‐latitude part of the cusp region.
Enhanced solar wind geoeffectiveness after a sudden increase in dynamic pressure during southward IMF orientation
Authors: Boudouridis A. , Zesta E. , Lyons L. R. , Anderson P. C. , Lummerzheim D.
Published: May 2005

It is well known that a persistent southward Interplanetary Magnetic Field (IMF) produces increased geomagnetic activity. It has recently been shown that a sudden increase in solar wind pressure results in poleward expansion of the auroral oval and closing of the polar cap over a wide range of MLTs, and this effect is more pronounced under southward IMF orientation. We show that southward IMF conditions combined with high solar wind dynamic pressure immediately after a pressure front impact lead to enhanced coupling between the solar wind and the terrestrial magnetosphere, significantly increasing the geoeffectiveness of the solar wind. We evaluate geoeffectiveness by the coupling efficiency, defined as the ratio of the cross‐polar‐cap potential measured by Defense Meteorological Satellite Program (DMSP) spacecraft to the cross‐magnetospheric potential calculated using solar wind parameters. We examine changes in the size of the polar cap and the coupling efficiency for a number of solar wind pressure enhancements under southward IMF configuration. We confirm the previously observed closing of the polar cap and show that there is a simultaneous increase of the coupling efficiency. This increase is measured for all cases, despite the fact that the magnetosphere is greatly compressed, and the increase is measured even when the solar wind electric field is reduced.
A numerical model of the dayside aurora
Authors: Yamamoto T. , Ozaki M.
Published: May 2005

A time‐independent model of the dayside auroras is presented within the framework of the pressure‐gradient‐driven mechanism for the generation of the region 1 field‐aligned current (FAC) in the low‐latitude boundary layer (LLBL). Either of two types of the dayside aurora, the bright spots (BSs) or the radially aligned arcs (RAs), arises from spatial modulation of the inner boundary of an LLBL particle population, but the respective source populations have different contents. BSs are produced when the boundary of a majority of the LLBL particle population is modulated. RAs are produced by large‐amplitude modulation occurring on a sharp boundary of a small fraction of the LLBL particle population. The required flux tube content, δN, of the source population of RAs is roughly 10% of that of the ambient population, if the scale length for ∇δN at the inner boundary is comparable to the magnetopause thickness. Using the 1989 Tsyganenko model, the FAC densities from the perturbed inner boundary of the particle population are evaluated and the energy fluxes of electrons precipitating to the ionosphere are then calculated on the basis of the Knight current‐voltage relation. This model can demonstrate the characteristic patterns of the RAs as well as the BSs. It also predicts that (1) both types of aurora with high luminosity as well as inverted‐V structures appear more frequently in the afternoon than in the morning, (2) this morning‐afternoon asymmetry is more pronounced for the case of BSs than RAs, and (3) during periods of northward interplanetary magnetic field, RAs can be distributed over a large area of the polar cap. Now the MLT‐dependent features of the dayside auroras, the appearances of “hot spot” and “warm spot,” and the large‐scale region 1 FAC generation can be understood systematically in view of the distortion of the (average) inner boundary of an LLBL particle population (i.e., nonalignment of the boundary with the average magnetic drift direction).
Artificial disturbances of the ionosphere over the Millstone Hill Incoherent Scatter Radar from dedicated burns of the space shuttle orbital maneuver subsystem engines
Authors: Bernhardt Paul A. , Erickson Philip J. , Lind Frank D. , Foster John C. , Reinisch Bodo W.
Published: May 2005

Two ionospheric modification experiments were carried out over the incoherent scatter radar (ISR) located at Millstone Hill, Massachusetts. These experiments are part of the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) program at the Naval Research Laboratory. The experiments use 10‐s burns of the dual orbital maneuver subsystem (OMS) engines to produce the injection of high‐speed molecules in the ionosphere near 380 km altitude. Charge exchange between the high‐speed exhaust molecules and the ambient oxygen ions yields molecular ion beams that disturb the natural state of the ionosphere. Radar scatter provides measurements of the ion velocity distributions and plasma turbulence that result from the ion beam interactions. Ground‐based observations with the University of Massachusetts Digisonde record the ionospheric density depressions resulting from recombination of the molecular ions with electrons. Prompt signatures of nonequilibrium ion distributions in the OMS engine plume are seen in the data taken during the SIMPLEX III and IV experiments for the space shuttle flights STS‐108 and STS‐110, respectively. The SIMPLEX III observations are much weaker than those during SIMPLEX IV. These differences are primarily attributed to the changes in the viewing directions for the radar beam. During SIMPLEX IV, the radar is looking more downstream from the exhaust injection and the stimulation of plasma turbulence is seen with the ISR for over 30 s at distances up to 200 km from the burn altitude along the radar beam. Strong backscatter in the radar spectra is attributed to ion acoustic waves driven by the pickup ion beams. Both experiments provide large‐scale cavities detected by the Digisonde for up to 20 min after the engine burn. These cavities are the result of ion‐electron recombination of the pickup ions.
Theoretical effects of geomagnetic activity on low‐latitude ionospheric electric fields
Authors: Huang C.‐M. , Richmond A. D. , Chen M.‐Q.
Published: May 2005

The influence of geomagnetic activity on middle‐ and low‐latitude thermospheric winds and ionospheric electric fields is investigated using model results from the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. Model runs are made for different levels of geomagnetic activity. Model results show that the equatorward ionospheric currents produced by disturbance winds develop positive charge accumulation at low latitudes that maximizes in the premidnight sector. The local time of maximum electric potential perturbation depends significantly on universal time so that the local time of reversal of the equatorial zonal perturbation electric field varies with longitude by 2 to 3 hours, depending on the intensity of geomagnetic activity. The westward perturbation electric field in the postsunset period indicates that stronger geomagnetic activity will produce a lower driven height of the evening F region. After geomagnetic activity ceases, model results show that the zonal disturbance winds can last for many days in the postrecovery period, while the meridional disturbance winds decay more rapidly. The long‐lasting zonal winds, through the Pedersen currents they drive, help maintain meridional disturbance potential drops that decay much more slowly than the zonal disturbance potential drops after the activity ceases.
Model‐data comparisons of shear waves in the nearshore
Authors: Noyes T. James , Guza R. T. , Feddersen Falk , Elgar Steve , Herbers T. H. C.
Published: May 2005

Observations of shear waves, alongshore propagating meanders of the mean alongshore current with periods of a few minutes and alongshore wavelengths of a few hundred meters, are compared with model predictions based on numerical solutions of the nonlinear shallow water equations. The model (after Özkan‐Haller and Kirby (1999)) assumes alongshore homogeneity and temporally steady wave forcing and neglects wave‐current interactions, eddy mixing, and spatial variation of the (nonlinear) bottom drag coefficient. Although the shapes of observed and modeled shear wave velocity spectra differ, and root‐mean‐square velocity fluctuations agree only to within a factor of about 3, aspects of the cross‐shore structure of the observed (∼0.5–1.0 m above the seafloor) and modeled (vertically integrated) shear waves are qualitatively similar. Within the surf zone, where the mean alongshore current (V) is strong and shear waves are energetic, observed and modeled shear wave alongshore phase speeds agree and are close to both V and Clin (the phase speed of linearly unstable modes) consistent with previous results. Farther offshore, where V is weak and observed and modeled shear wave energy levels decay rapidly, modeled and observed C diverge from Clin and are close to the weak alongshore current V. The simulations suggest that the alongshore advection of eddies shed from the strong, sheared flow closer to shore may contribute to the offshore decrease in shear wave phase speeds. Similar to the observations, the modeled cross‐ and alongshore shear wave velocity fluctuations have approximately equal magnitude, and the modeled vorticity changes sign across the surf zone.
Interannual and decadal variability of the western Pacific sea surface condition for the years 1787–2000: Reconstruction based on stable isotope record from a Guam coral
Authors: Asami Ryuji , Yamada Tsutomu , Iryu Yasufumi , Quinn Terrence M. , Meyer Christopher P. , Paulay Gustav
Published: May 2005

We present a monthly resolved, 213‐year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (δ18Ocoral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The δ18Ocoral anomaly reflects sea surface temperature (SST) anomaly and sea surface salinity (SSS) anomaly with significant r values of −0.69 and 0.49, respectively, which are strongly linked to oceanographic changes that occur during El Niño–Southern Oscillation (ENSO) warm and cool phases. We identified 46 ENSO warm (El Niño) and 53 cool phases (La Niña) in the coral record, which are consistent with those phases reconstructed by Niño 3.4 SST anomaly. Spectral analyses of the δ18Ocoral anomaly record for the years 1790–1999 identified significant peaks around ∼3 to ∼7 years. These results indicate that the Guam coral has recorded ENSO periodicity. The δ18Ocoral anomaly shows decadal variability of ∼15‐ to ∼45‐year periodicity with significant shifts (<0.2‰) from warmer to cooler condition and vice versa. An accumulative decrease in δ18Ocoral time series may imply ∼0.75°C warming of SST and ∼0.23‰ freshening of seawater δ18O, corresponding to a decrease of SSS by ∼0.85, in the northwestern tropical Pacific over the last 2 centuries.
On the sedimentological origin of down‐core variations of bulk sedimentary nitrogen isotope ratios
Authors: Kienast M. , Higginson M. J. , Mollenhauer G. , Eglinton T. I. , Chen M.‐T. , Calvert S. E.
Published: May 2005

The bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the South China Sea (Site 17940 and Ocean Drilling Program (ODP) Site 1144) differs by up to >2‰ during the last glacial period. Given their close proximity, both core sites are located in the same biogeographic zone and nutrient regime, and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions. In an attempt to resolve this offset, we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary δ15N, namely, the variable contribution of inorganic N to bulk N in the sediment and the grain‐size dependence of bulk δ15N. We find that neither effect, singly or in combination, is sufficient to explain the significant δ15N offset between the two down‐core records. By elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site. This study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts, such as ODP Site 1144.
Diatom stable isotopes, sea ice presence and sea surface temperature records of the past 640 ka in the Atlantic sector of the Southern Ocean
Authors: Schneider‐Mor Aya , Yam Ruth , Bianchi Cristina , Kunz‐Pirrung Martina , Gersonde Rainer , Shemesh Aldo
Published: May 2005

High‐resolution δ13C and δ15N records of diatom‐bound organic matter (δ13CD, δ15ND) from ODP site 1094, South of the Polar Front, are combined with reconstructions of summer sea surface temperature and winter sea‐ice to establish changes in surface water characteristics associated with the main climatic events of the past 640 ka. The six glacial‐interglacial δ13CD cycles show excellent agreement with SPECMAP δ18O and Vostok CO2 content, suggesting that global physical processes rather than local biological factors were the main influences on δ13CD. By contrast, there is weak correspondence between the Vostok dust record and the δ13CD and δ15ND records. The data do not support the hypothesis that glacial iron fertilization of the Southern Ocean was the main factor lowering atmospheric CO2, if dust accumulation represents iron input. The records indicate that sea ice cover, water column stratification and iron addition from deep water mixing are more likely to explain our observations.
On sea ice concentration anomaly coherence in the southern Beaufort Sea
Authors: Lukovich Jennifer V. , Barber David G.
Published: May 2005

The circumpolar flaw lead polynya system is a region of enhanced biological productivity and for significant portions of the annual cycle, dominates the exchange of energy and mass across the ocean‐sea ice‐atmosphere (OSA) interface. We investigate the nature of sea ice concentration (SIC) anomalies for spatial and temporal statistical persistence within a portion of this flaw lead system. We find such a structure in the shelf break zone between Amundsen Gulf and the Canada Basin. NCEP/NCAR reanalysis data is used to determine the potential roles of oceanic and atmospheric forcing in creating and maintaining this observed coherence in the SIC anomalies. Results suggest that the coherence pattern is consistent over the instrumental record (1979 to 2000), although it changes in shape and extent between years. The forcing mechanisms creating this coherence in SIC anomalies appear to be tied to surface wind‐driven upwelling in the shelf‐break areas of the Southern Beaufort Sea (SBS).
Preliminary analysis of volcanoseismic signals recorded at the Tatun Volcano Group, northern Taiwan
Authors: Lin C. H. , Konstantinou K. I. , Liang W. T. , Pu H. C. , Lin Y. M. , You S. H. , Huang Y. P.
Published: May 2005

The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei. A seismic array consisting of 5 stations equipped with both broadband and short‐period sensors was installed in 2003 in order to monitor the seismic activity of the area. It recorded a variety of events including common volcano‐tectonic earthquakes and volcanoseismic signals like tornillos, short duration monochromatic events (10–15 s) and long duration spasmodic bursts (∼15 min). An analysis of the complex frequencies of the tornillo/monochromatic signals shows that Q‐values are of the order of several hundreds. Based on the model of a fluid‐filled crack, such Q‐values can result from the oscillations of a crack containing a misty or dusty gas. These observations put into doubt the long‐standing suggestion that the Tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area.
Atmospheric induced oceanic tides from ECMWF forecasts
Authors: Dobslaw Henryk , Thomas Maik
Published: May 2005

The usability of ECMWF's forecasts for the determination of diurnal and semidiurnal mass variations in the atmosphere‐ocean system due to atmospheric pressure tides is examined and contrasted to corresponding variabilities deduced from ECMWF's analyses. While the diurnal pressure tide and the oceanic response simulated with a baroclinic ocean model are well resolved from both analyses and forecasts, the semidiurnal tide can be recovered from 3 hourly forecasts only. In terms of rms values of geoid height anomalies, forecast errors cause 0.18 mm, different wind representations 0.09 mm, and the doubled temporal resolution 0.20 mm of deviations between forecasts and analyses. Since atmospheric tides are highly variable, a time‐invariant harmonic approach might not meet high precision requirements as for the GRACE mission and for high‐resolution Earth rotation parameters. Considering these forecast errors, forecasts allow to account for atmospheric variability and corresponding oceanic responses down to semidiurnal timescales, dispensing with any additional model of atmospheric tides.
High‐energy solar particles and human exploration
Authors: Lanzerotti Louis J.
Published: May 2005

An adequate understanding of solar activity, including its predictability for producing conditions that can give rise to high‐energy ions that can penetrate spacecraft and space suits, is woefully lacking if the United States intends to proceed with the vision that has now been articulated for the nation's civil, human‐flight space program: back to the Moon and on to Mars.
Seedling recruitment of the exotic grass Andropogon gayanus (Poaceae) in northern Australia
Authors: Flores Trish A. , Setterfield Samantha A. , Douglas Michael M.
Published: May 2005

Andropogon gayanus Kunth. (Gamba grass), a tall perennial grass from Africa, is invading savanna ecosystems in northern Australia. This study investigated A. gayanus recruitment to determine the habitats at risk of invasion and to provide recommendations for its management. A. gayanus is able to establish and spread into new areas because of its high seed production (averaging 70 000 seeds m–2) and ability to establish across a range of habitats: from open woodlands on relatively dry lateritic soils to the more closed forests on black soil of the floodplain margins. Seedling emergence occurred in the absence of soil cultivation, although soil cultivation did increase emergence in the wetter habitats (Melaleuca uplands and floodplain margins). Seedling survival was high in the savanna (~90%) but low in the wetter habitats owing to wet-season inundation. A seed longevity trial based on burying seed in the field and retrieving between 1 and 12 months after burial showed that less than 1% of seeds survived in the seedbank after 12 months. Effective control programs are needed immediately because of the vast area and range of habitats in northern Australia that could potentially be invaded by A. gayanus. Management that can limit site disturbance and seed production, and can incorporate follow-up control for one to two years, should be an important part of an A. gayanus control strategy.
Intra-specific variation in carbohydrate reserves and sprouting ability in Eucalyptus obliqua seedlings
Authors: Walters Judi R. , Bell Tina L. , Read Steve
Published: May 2005

Seedlings of 13 provenances of Eucalyptus obliqua L’Hér. grown under favourable moisture and nutrient conditions in a glasshouse for 9 months showed significant differences in seedling height, lignotuber size and carbohydrate reserve pools in roots and lignotubers. Lignotuber size was strongly and inversely correlated with mean annual rainfall of the source provenance, and larger E. obliqua lignotubers had higher concentrations and pools of carbohydrate reserves than smaller lignotubers. When seedling stems were clipped just above the lignotuber to simulate grazing or damage by fire, clipped seedlings showed significantly different responses to disturbance; seedlings with large carbohydrate reserve pools produced more sprouts of greater dry weight than seedlings with small carbohydrate reserve pools. The sprouting ability of lignotubers was related to carbohydrate reserves, such that plants with larger reserves in the lignotubers and roots supported production of a greater number of sprouts of greater total biomass than plants with smaller reserves. These results suggest that the sprouting mechanism provided by lignotubers is more important for seedling survival in areas of lower rainfall.
Zoosporic fungi from Australian and New Zealand tree-canopy detritus
Authors: Longcore Joyce E.
Published: May 2005

The canopy of rainforest trees is an example of a species-rich habitat; however, most of the species known are invertebrates. Zoosporic fungi live in water and soils throughout the world, but have not been reported from the organic detritus of the rainforest canopy. I added water and baits to samples of Australian and New Zealand canopy detritus, and recovered zoosporic fungi representing three major phylogenetic groups, the Chytridiomycota, Oomycota and Hyphochytriomycota. Queensland samples yielded seven chytrid species, a hyphochytrid species and two members of the Saprolegniales. New Zealand samples yielded five chytrids and one member of the Saprolegniales. Most of these fungi were species that have been reported from terrestrial soils or that belong to typically soil-inhabiting groups. Most of the chytrids were isolated into pure cultures and illustrations of their developmental stages are included.
The origin and anatomy of rhizophores in Vernonia herbacea and V. platensis (Asteraceae) from the Brazilian Cerrado
Authors: Hayashi Adriana Hissae , Appezzato-da-Glória Beatriz
Published: May 2005

The aim of this work is to study the origin and anatomy of rhizophores in two Asteraceae species from the Brazilian Cerrado: Vernonia herbacea (Vell.) Rusby and V. platensis (Spreng.) Less. In both species, axillary buds from the cotyledonary node give rise to the first rhizophores. As rhizophores develop, these organs branch to form new rhizophores from their axillary buds that constitute a sympodial system of underground branches. Nodes, internodes and axillary buds, protected by cataphylls, are evident in these underground organs. The primary root degenerates and all the root system arises adventitiously from the rhizophores. Under natural conditions, the axillary buds give rise to new rhizophores, but when exposed to the light, these buds develop into aerial stems. When rhizophores are fragmented, each of these structures, which accumulate fructans, are important organs for vegetative propagation mainly in areas subjected to environmental disturbances, such as the Cerrado, where fire and drought frequently occur.
Seedling recruitment, seed persistence and aspects of dispersal ecology of the invasive moth vine, Araujia sericifera (Asclepiadaceae)
Authors: Vivian-Smith Gabrielle , Panetta F. Dane
Published: May 2005

We investigated germination, seedling emergence and seed persistence of the invasive moth vine (Araujia sericifera Brot.) under controlled and field conditions in south-eastern Queensland. Fresh seed showed high viability (99.5%) and germinated readily, with 97.2% of all recorded germinations occurring within 14 days. Mean germination rates ranged from 74 to 100% across the range of temperature (10/20°C, 15/25°C and 20/30°C alternating 12-h thermoperiods) and light (0- and 12-h photoperiods) treatments. Germination was significantly reduced only under cool, dark conditions. In a 24-month field experiment, seedling emergence was greatest for seeds buried at 1 cm (mean = 96.3%), intermediate for seeds buried at 5 cm (mean = 62.7%) and least for surface-sown seeds (mean = 30.7%). Seed persistence under field conditions was low, declining rapidly to 3.9% at 6 months and to 0.67% at 24 months. Moth vine’s capacity to germinate readily and the rapid depletion of seeds under field conditions indicate that the species has a transient seed bank in south-eastern Queensland. In an additional experiment testing the capacity of seeds for secondary dispersal by water, the mean floating time of seeds was 15.4 days, suggesting that water could act as a secondary dispersal vector, contributing to long-distance dispersal. We recommend that surveillance methods for detecting moth-vine populations should consider both water-flow patterns and wind direction.
Diverted total synthesis: Preparation of a focused library of latrunculin analogues and evaluation of their actin-binding properties
Authors: Fürstner Alois , Kirk Douglas , Fenster Michaël D. B. , Aïssa Christophe , De Souza Dominic , Müller Oliver
Published: May 2005

Two largely catalysis-based and highly convergent total syntheses of latrunculin A (
1
) and B (
2
) were diverted to the preparation of a focused library of analogues of these potent actin-binding macrolides that enjoy widespread use in chemical biology. Because the chosen route allows for structural variations of all characteristic parts of the natural leads, it was possible to map the previously largely unknown structure/activity profile of this class of bioactive natural products. This led to the discovery that the removal of the methyl branches decorating the macrocycle in 2 engenders a significant increase in potency, while streamlining the synthesis to a considerable extent. Moreover, compelling evidence is provided that the conspicuous 2-thiazolidinone ring present in all naturally occurring latrunculins may be an optimal but not an essential structural motif for actin binding because it can be replaced by an oxazolidinone moiety with only slight loss in efficacy. Likewise, the inversion of the absolute configuration of the chiral center at C.16 is well accommodated. From the purely chemical perspective, this investigation attests to the maturity of alkyne metathesis, a method that has received attention as efficient means for the formation of macrocycles only recently.
Derivation of germ-line-competent embryonic stem cell lines from preblastocyst mouse embryos
Authors: Tesar Paul J.
Published: May 2005

The first differentiation event of the mammalian embryo is thought to occur during blastulation and results in two populations of cells, the inner cell mass (ICM) and the trophectoderm. Most embryonic stem (ES) cell lines have been derived from the ICM or a further subset of ICM cells known as the epiblast. There appears to be a limited period of embryonic development during which pluripotent ES cells can be adapted from the cells of the blastocyst to culture. A method is presented here that allows ES cell lines to be isolated from preblastocyst mouse embryos. These lines were derived from 129S2/SvHsd mouse morulae and earlier cleavage stages with high efficiency. The lines expressed genes and antigens characteristic of pluripotent ES cells. XY cell lines remained karyotypically stable through extensive passaging and produced germ-line-competent chimeras upon blastocyst injection. These results suggest that true ES cells can be derived from embryos explanted at any stage of preimplantation development in the mouse. This finding raises the interesting question of whether ES cell lines derived from embryos at different stages of preimplantation development possess the same potential.
Positively charged retinoids are potent and selective inhibitors of the trans-cis isomerization in the retinoid (visual) cycle
Authors: Golczak Marcin , Kuksa Vladimir , Maeda Tadao , Moise Alexander R. , Palczewski Krzysztof
Published: May 2005

In vertebrate retinal photoreceptors, photoisomerization of opsin-bound visual chromophore 11-
cis
-retinal to
all-trans
-retinal triggers phototransduction events. Regeneration of the chromophore is a critical step in restoring photoreceptors to their dark-adapted state. This regeneration process, called the retinoid cycle, takes place in the photoreceptor outer segments and in the retinal pigmented epithelium (RPE). We have suggested that the regeneration of the chromophore might occur through a retinyl carbocation intermediate. Here, we provide evidence that isomerization is inhibited by positively charged retinoids, which could act as transition state analogs of the isomerization process. We demonstrate that retinylamine (Ret-NH
2
) potently and selectively inhibits the isomerization step of the retinoid cycle
in vitro
and
in vivo
. Ret-NH
2
binds a protein(s) in the RPE microsomes, but it does not bind RPE65, a protein implicated in the isomerization reaction. Although Ret-NH
2
inhibits the regeneration of visual chromophore in rods and, in turn, severely attenuates rod responses, it has a much smaller effect on cone function in mice. Ret-NH
2
interacts only at micromolar concentrations with retinoic acid receptor, does not activate retinoid-X receptor, and is not a substrate for CYP26s, the retinoic acid-metabolizing cytochrome P450 enzymes. Ret-NH
2
can be a significant investigational tool to study the mechanism of regeneration of visual chromophore.
Effect of ammonia concentration on rumen microbial protein production in vitro
Authors: Satter L. D , Slyter L. L
Published: May 2005

1. The effect of ammonia concentration on microbial protein production was determined in continuous-culture fermentors charged with ruminal contents obtained from steers fed on either a protein-free purified diet, a maize-based all-concentrate diet, or a forage–concentrate (23:77) diet. Urea was infused into the fermentors to maintain various concentrations of ammonia in the incubating mixtures.

2. Under nitrogen-limiting conditions, microbial protein yield measured as tungstic acid-precipitable N (TAPN) increased linearly with supplementary urea until ammonia started to accumulate in the incubating ingesta. Increasing the ammonia concentration beyond 50 mg NH3-N/l had no effect on microbial protein production.

3. The molar proportions of volatile acids produced were not affected by the level of urea supplementation. Total acid production was decreased slightly under N-limiting conditions, but not to the same extent as microbial protein production.

4. Estimated yield of microbial dry matter/mol ATP produced averaged 15·6 when non-limiting N as urea was provided with the purified diet.

5. These results suggest that addition of non-protein N supplements to ruminant rations are warranted only if the prevailing concentration of ruminal ammonia is less than 50 mg NH3-N/l ruminal fluid.
Studies on the growth and changes in metabolism of rats fed on carbohydrate-deficient fatty acid based diets supplemented with graded levels of maize starch
Authors: Akrabawi S. S , Saegert Merry M. , Salji J. P
Published: May 2005

1. Experiments were conducted to determine the effects of the supplementation of carbohydrate-deficient fatty acid-based (FA) diets with 18·7, 37·5, 75, 150 and 300 g maize starch (MS)/kg on the growth and metabolism of the growing rat. Further, the effects of fasting on rats given the FA diet were compared with those given the high-carbohydrate (CHO) diet. Due to the significant decrease in food consumption of rats given the FA diet, the effects of pair-feeding the CHO and the FA diet were also investigated.

2. The isoenergetic replacement of fatty acids with increasing amounts of MS in the FA diet given to rats increased their weight gain and concentration of glucose in their plasma. These increases, however, tended to level off for weight gain and glucose concentration, respectively, at about 18·7 g and 75 g MS/kg diet. The same type of replacement decreased the concentration of ketones in the plasma but the decrease levelled off at the high concentration of 300 g MS/kg diet. Activities of liver glucose-6-phosphatase (EC3.1.3.9) and glucokinase (EC2.7.1.2) decreased and increased respectively with increasing concentration of maize starch in the diet. These changes tended to level off at concentrations of about 75–150 g MS/kg diet.

3. Fasting for 18 h decreased the concentration of glucose in plasma of both the FA- and the CHO-fed rats, while fasting of the CHO-fed rats depressed the concentration of glycogen in the liver but did not influence that of the FA-fed rats. Pair-feeding the CHO diet to the FA diet produced similar weight increases during the 8-week experimental period.
Force-feeding effects on growth, carcass and blood composition in the young chick
Authors: Nir I , Shapira Niva , Nitsan Zafrira , Dror Y
Published: May 2005

1. Excessive amounts of food (70% greater thanad lib. intake) introduced into the gastrointestinal tract of young chicks were efficiently digested and caused increased growth resulting mainly from lean body substance and partially from fat deposition, more efficient energy utilization than thead lib.-fed controls, increased relative weights of the crop, proventriculus, intestine, liver and abdominal adipose tissue. Pancreas relative weight was not changed and that of the gizzard was reduced.

2. The treatment also caused changes in blood plasma composition. Free fatty acid, trigly-ceride, α2-, β- and γ-globulin and pre-β-lipoprotein concentrations increased.

3. Fasting for 30 h caused higher body fat losses and lower body protein losses in the force-fed chicks than in thead lib.-fed chicks.

4. The effects of over-feeding on body and blood plasma composition and differences found in these measurements during starvation are discussed.
The effects of force-feeding on enzymes of the liver, kidney, pancreas and digestive tract of chicks
Authors: Nitsan Zafrira , Dror Y , Nir I. , Shapira Niva
Published: May 2005

1. Force-feeding of young chicks for 15 d increased kidney arginase (EC3·5·3·1) activity threefold. Fasting for 30 h decreased this activity by 50%.

2. Liver xanthine dehydrogenase was slightly increased after force-feeding and decreased following fasting.

3. The specific activities of two pentose-phosphate-cycle enzymes were not significantly affected by force-feeding, but glucose-6-phosphate dehydrogenase (EC1.1.1.49) decreased following fasting.

4. The over-all secretion of digestive enzymes increased parallel to the increase in food consumption. Therefore, despite an increased absolute weight of the pancreas and intestinal chyme, specific activities were the same in the force-fed andad lib.-fed groups, except for a higher activity in intestinal amylase.

5. Fasting did not affect the pancreatic enzymic activities.