bluuebunny/crossref_metadata_2025 huggingface dataset:
Optoacoustic imaging using interferometric measurement of surface displacement
Authors: Carp Stefan A. , Guerra Arnold , Duque Samuel Q. , Venugopalan Vasan
Published: December 2004

We describe an optoacoustic imaging technique based on time-resolved measurements of laser-induced thermoelastic expansion. Tomographic images of tissue phantoms are formed using such measurements made at several locations following irradiation with a Q-switched Nd:YAG (λ=1064nm) laser pulse. Our system is based on a modified Mach–Zehnder interferometer that measures surface displacement with a temporal resolution of 4ns and a displacement sensitivity of 0.3nm. Images formed from data sets acquired from several highly scattering tissue phantoms provide better than 200μm resolution and show great promise for high-resolution noninvasive imaging of heterogeneous tissues at depths approaching 1cm.
Distributed feedback regime of photonic crystal waveguide lasers at 1.5μm
Authors: Checoury X. , Boucaud P. , Lourtioz J-M. , Pommereau F. , Cuisin C. , Derouin E. , Drisse O. , Legouezigou L. , Lelarge F. , Poingt F. , Duan G. H. , Mulin D. , Bonnefont S. , Gauthier-Lafaye O. , Valentin J. , Lozes F. , Talneau A.
Published: December 2004

Lasing of W3 and W2∕3 triangular lattice photonic crystal waveguides on InP substrate is investigated around 1.5μm by optical pumping. The lattice period of the fabricated structures is varied from 320 to 540nm by steps of 20nm, thereby leading to a detailed exploration of the lasing mechanism over a large frequency range. A distributed-feedback-laser- (DFB-) like-emission is observed above the gap (W3), while a genuine DFB laser emission is obtained in the gap (W2∕3). Side-mode suppression ratios can reach 40dB when an antireflecting coating is used on the cleaved output facet. Experimental results including light–light characteristics are analyzed in the framework of two-dimensional plane-wave calculations.
Patterned growth of pentacene
Authors: Steudel Soeren , Janssen Dimitri , Verlaak Stijn , Genoe Jan , Heremans Paul
Published: December 2004

We propose a way of patterning organic small molecule thin films without requiring a hardmask and therefore more compatible with printing technologies. Active and passive areas for transistors are predefined by different surface chemistries. The subsequent growth takes place under conditions that cause the formation of a high mobility two-dimensional film in the active area and a disconnected three-dimensional film or no film in the passive area. This concept is founded on the basic theory of nucleation of organic small molecules on inert substrates and applied to the growth of patterned pentacene layers.
Quantitative investigations of optical absorption in InAs∕InP(311)B quantum dots emitting at 1.55μm wavelength
Authors: Cornet C. , Labbé C. , Folliot H. , Bertru N. , Dehaese O. , Even J. , Le Corre A. , Paranthoen C. , Platz C. , Loualiche S.
Published: December 2004

We have measured the absorbance of InAs∕InP quantum dots emitting at 1.55μm wavelength with a Fourier transform infrared spectrometer. The sample is a 12-stack InAs quantum dots grown by molecular beam epitaxy on (311)BInP oriented substrate. The absorption coefficient is estimated at 4400cm−1 for 3nm height and 5×1010cm−2 surface density. The absorption of the quantum dot structures is found to be similar to quantum well structures when the number of atoms considered absorbing is equivalent. The Stokes shift between the absorbance and the photoluminescence spectra is also investigated at 4 and 293K.
Tunable optical switch using magnetic fluids
Authors: Horng H. E. , Chen C. S. , Fang K. L. , Yang S. Y. , Chieh J. J. , Hong Chin-Yih , Yang H. C.
Published: December 2004

With a tunable refractive index, magnetic fluid can be applied to the development of adjustable optical devices. In this work, a magnetic-fluid-based optical switch is designed and characterized. The optical switch is formed by sealing magnetic fluid between two glass prisms. When a light is incident to one side of one of the prisms, a reflected light from the magnetic fluid film comes out from the same prism, whereas a transmitted light through the film emits from the other prism. It was found that the intensity ratio of the reflected light to the transmitted light can be manipulated by varying the external magnetic field strength. This implies that the light intensity can be switched between two paths. The switching efficiency also depends on the incident angle of a light into the prism. We then theoretically derive the incident-angle dependent switching efficiency to clarify relevant physical mechanisms.
Magnetic-field-controllable avalanche breakdown and giant magnetoresistive effects in Gold∕semi-insulating-GaAs Schottky diode
Authors: Sun Z. G. , Mizuguchi M. , Manago T. , Akinaga H.
Published: December 2004

Gold (Au)∕semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current–voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2T, avalanche breakdown was totally quenched. When Au-SI-GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8T.
Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering
Authors: Chen Liang-Yih , Chen Wen-Hwa , Wang Jia-Jun , Hong Franklin Chau-Nan , Su Yan-Kuin
Published: December 2004

Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4Ωcm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorption increased with increasing H2 composition. The phenomenon is interpreted as the filling of conduction band by electrons in n-type semiconductor.
Planteose is a short-term storage carbohydrate in Actinidia leaves
Authors: Klages Karin U. , Boldingh Helen L. , Cooney Janine M. , MacRae Elspeth A.
Published: December 2004

The polyol myo-inositol constitutes 10–20% of soluble carbohydrates in mature leaves of Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson var. deliciosa ‘Hayward’ and A. arguta (Sieb. et Zucc.) Planch. ex Miq. var. arguta. In contrast with other non-structural carbohydrates, myo-inositol concentrations in A. deliciosa leaves increase only slightly during development from sink to source, and are not affected in source leaves by increased sink demand upon fruit set. In mature fruit-bearing leaves myo-inositol concentrations fluctuate diurnally, increasing during the night and declining towards morning, but in plants with less sink demand a diurnal pattern is not observed. In potted A. arguta seedlings subjected to extended dark periods, leaf concentrations of sugars and starch decline rapidly while myo-inositol concentrations are maintained. Labelling studies with 14CO2 revealed that myo-inositol in leaves is not a primary photosynthetic product and is turned over more slowly than other soluble carbohydrates. A suggested role of myo-inositol as a precursor in mucilage synthesis was not substantiated, as radioactivity was incorporated into mucilage more rapidly than into free myo-inositol. Planteose, a trisaccharide comprising sucrose and galactose, incorporated substantial amounts of radioactivity and accumulated to high levels, indicating a role in short-term storage of sucrose. Planteose was synthesised during the day and degraded during the night in a manner that was opposite to that of sucrose while starch and myo-inositol levels remained relatively constant. Planteose has been reported in Cyclamen persicum, ash and sesame seed. This is the first report of planteose in Actinidia, and the first time it has been identified as a major short-term storage carbohydrate in Actinidia leaves.
Effect of elevated CO2 concentration and vapour pressure deficit on isoprene emission from leaves of Populus deltoides during drought
Authors: Pegoraro Emiliano , Rey Ana , Bobich Edward G. , Barron-Gafford Greg , Grieve Katherine Ann , Malhi Yadvinder , Murthy Ramesh
Published: December 2004

To further our understanding of the influence of global climate change on isoprene production we studied the effect of elevated [CO2] and vapour pressure deficit (VPD) on isoprene emission rates from leaves of Populus deltoides Bartr. during drought stress. Trees, grown inside three large bays with atmospheres containing 430, 800, or 1200 μmol mol–1 CO2 at the Biosphere 2 facility, were subjected to a period of drought during which VPD was manipulated, switching between low VPD (approximately 1 kPa) and high VPD (approximately 3 kPa) for several days. When trees were not water-stressed, elevated [CO2] inhibited isoprene emission and stimulated photosynthesis. Isoprene emission was less responsive to drought than photosynthesis. As water-stress increased, the inhibition of isoprene emission disappeared, probably as a result of stomatal closure and the resulting decreases in intercellular [CO2] (Ci). This assumption was supported by increased isoprene emission under high VPD. Drought and high VPD dramatically increased the proportion of assimilated carbon lost as isoprene. When measured at the same [CO2], leaves from trees grown at ambient [CO2] always had higher isoprene emission rates than the leaves of trees grown at elevated [CO2], demonstrating that CO2 inhibition is a long-term effect.
Protein engineering of cytochrome
b
562
for quinone binding and light-induced electron transfer
Authors: Hay Sam , Wallace Brett B. , Smith Trevor A. , Ghiggino Kenneth P. , Wydrzynski Tom
Published: December 2004

The central photochemical reaction in photosystem II of green algae and plants and the reaction center of some photosynthetic bacteria involves a one-electron transfer from a light-activated chlorin complex to a bound quinone molecule. Through protein engineering, we have been able to modify a protein to mimic this reaction. A unique quinone-binding site was engineered into the
Escherichia coli
cytochrome
b
562
by introducing a cysteine within the hydrophobic interior of the protein. Various quinones, such as
p
-benzoquinone and 2,3-dimethoxy-5-methyl-1,4-benzoquinone, were then covalently attached to the protein through a cysteine sulfur addition reaction to the quinone ring. The cysteine placement was designed to bind the quinone ≈10 Å from the edge of the bound porphyrin. Fluorescence measurements confirmed that the bound hydroquinone is incorporated toward the protein's hydrophobic interior and is partially solvent-shielded. The bound quinones remain redox-active and can be oxidized and rereduced in a two-electron process at neutral pH. The semiquinone can be generated at high pH by a one-electron reduction, and the midpoint potential of this can be adjusted by ≈500 mV by binding different quinones to the protein. The heme-binding site of the modified cytochrome was then reconstituted with the chlorophyll analogue zinc chlorin e
6
. By using EPR and fast optical techniques, we show that, in the various chlorin–protein–quinone complexes, light-induced electron transfer can occur from the chlorin to the bound oxidized quinone but not the hydroquinone, with electron transfer rates in the order of 10
8
s
–1
.
Crystal structure of the human ATP-dependent splicing and export factor UAP56
Authors: Shi Hang , Cordin Olivier , Minder C. Michael , Linder Patrick , Xu Rui-Ming
Published: December 2004

Pre-mRNA splicing requires the function of a number of RNA-dependent ATPases/helicases, yet no three-dimensional structure of any spliceosomal ATPases/helicases is known. The highly conserved DECD-box protein UAP56/Sub2 is an essential splicing factor that is also important for mRNA export. The expected ATPase/helicase activity appears to be essential for the UAP56/Sub2 functions. Here, we show that purified human UAP56 is an active RNA-dependent ATPase, and we also report the crystal structures of UAP56 alone and in complex with ADP, as well as a DECD to DEAD mutant. The structures reveal a unique spatial arrangement of the two conserved helicase domains, and ADP-binding induces significant conformational changes of key residues in the ATP-binding pocket. Our structural analyses suggest a specific protein-RNA displacement model of UAP56/Sub2. The detailed structural information provides important mechanistic insights into the splicing function of UAP56/Sub2. The structures also will be useful for the analysis of other spliceosomal DExD-box ATPases/helicases.
Economic Growth and Medicare Funding Systems
Authors: Hau Arthur , Jiang Lily
Published: December 2004

This article compares the long‐run effects of changes in health conditions, population growth, price of medical care, and Medicare indemnity rate on capital formation and medical expenditures under fully funded and pay‐as‐you‐go Medicare. Surprisingly, it is found that population growth, rising medical prices, and increasingly adverse health conditions may or may not raise medical expenditures in the long run. Moreover, the directions of some of these effects under the pay‐as‐you‐go Medicare system are reversed under the fully funded system. Finally, it is shown that fully funded Medicare results in higher steady‐state capital than pay‐as‐you‐go Medicare; however, the welfare effect of the former may or may not be higher than that of the latter in general. (JEL H550, E620)
Welfare Payments and the Spread of HIV in the United States
Authors: Ressler Rand W. , Waters Melissa S. , Hill R. Carter , Watson John Keith
Published: December 2004

Clarke and Strauss (1998), among others, have determined that the magnitude of financial transfers to unwed mothers is positively related to out‐of‐wedlock fertility rates. Increases in fertility rates must be accompanied by increases in unprotected sex, and unprotected sex allows for the spread of sexually transmitted diseases. We hypothesize that states with relatively greater welfare payments under the old Aid to Families with Dependant Children (AFDC) program are associated with higher rates of heterosexually contracted human immunodeficiency virus (HIV). Using data for 26 reporting states from 1993 to 1996, our weighted instrumental variables estimates with clustered standard errors are consistent with our hypothesis. (JEL D1, I38)
Excessive Government Fee Collection in China
Authors: Lin Shuanglin
Published: December 2004

There are several thousand administrative and operating fees, compared to 23 taxes in China. Excessive fee collections are largely targeted at business enterprises and farmers. The growth of fee collection resulted from the increase in the gap between government expenditures and revenues, the self‐collection and self‐utilization policy, and weak law enforcement. Excessive fee collection tends to reduce businesses’investment incentive, aggravate income inequality, breed corruption, and distort the fiscal system. Fee reduction is not possible if the government size and revenue shortage problems of local governments persist. Policy options such as cutting government size are recommended. (JEL H20, H87, P35)
The Gender Pay Gap by Occupation: A Test of the Crowding Hypothesis
Authors: Solberg Eric J.
Published: December 2004

Identified, structural wage equations for seven occupations are estimated to test the crowding hypothesis—that the gender pay gap is due to females being crowded into low‐paying occupations—using data drawn from the 1996 wave of the National Longitudinal Study of Youth (NLSY79). Occupational preferences are used to estimate a logit probability model of occupational assignment to create instruments to control for self‐selection. Wage equations are estimated for all workers and for full‐time, year‐round workers. Identical specifications are estimated for private‐sector workers. The results are not consistent with a crowding explanation as the sole source of the gender pay gap unless crowding occurs at less aggregated levels of occupations than those used for this study. (JEL J16, J31, J71)
Diffraction, crystallography and microscopy beyond three dimensions: structural dynamics in space and time
Authors: Zewail Ahmed H.
Published: December 2004

In this article we highlight recent developments of ultrafast electron diffraction and crystallography at Caltech. These developments have made it possible to resolve transient structures, both spatially (0.01 Å) and temporally (picosecond and now femtosecond), in the gas phase and condensed media—surfaces, interfaces, and crystals—with wide-ranging applications. With the extension to ultrafast electron microscopy, discussed here and elsewhere, we present an overview of one major research area at our centre, the Laboratory for Molecular Sciences.
Tropical forest tree mortality, recruitment and turnover rates: calculation, interpretation and comparison when census intervals vary
Authors: LEWIS SIMON L. , PHILLIPS OLIVER L. , SHEIL DOUGLAS , VINCETI BARBARA , BAKER TIMOTHY R. , BROWN SANDRA , GRAHAM ANDREW W. , HIGUCHI NIRO , HILBERT DAVID W. , LAURANCE WILLIAM F. , LEJOLY JEAN , MALHI YADVINDER , MONTEAGUDO ABEL , NÚÑEZ VARGAS PERCY , SONKÉ BONAVENTURE ,   NUR SUPARDI, M.N.  , TERBORGH JOHN W. , VÁSQUEZ MARTÍNEZ RODOLFO
Published: December 2004

Mathematical proofs show that rate estimates, for example of mortality and recruitment, will decrease with increasing census interval when obtained from censuses of non‐homogeneous populations. This census interval effect could be confounding or perhaps even driving conclusions from comparative studies involving such rate estimates.

We quantify this artefact for tropical forest trees, develop correction methods and re‐assess some previously published conclusions about forest dynamics.

Mortality rates of > 50 species at each of seven sites in Africa, Latin America, Asia and Australia were used as subpopulations to simulate stand‐level mortality rates in a heterogeneous population when census intervals varied: all sites showed decreasing stand mortality rates with increasing census interval length.

Stand‐level mortality rates from 14 multicensus long‐term forest plots from Africa, Latin America, Asia and Australia also showed that, on average, mortality rates decreased with increasing census interval length.

Mortality, recruitment or turnover rates with differing census interval lengths can be compared using the mean rate of decline from the 14 long‐term plots to standardize estimates to a common census length using λcorr = λ × t0.08, where λ is the rate and t is time between censuses in years. This simple general correction should reduce the bias associated with census interval variation, where it is unavoidable.

Re‐analysis of published results shows that the pan‐tropical increase in stem turnover rates over the late 20th century cannot be attributed to combining data with differing census intervals. In addition, after correction, Old World tropical forests do not have significantly lower turnover rates than New World sites, as previously reported. Our pan‐tropical best estimate adjusted stem turnover rate is 1.81 ± 0.16% a−1 (mean ± 95% CI, n = 65).

As differing census intervals affect comparisons of mortality, recruitment and turnover rates, and can lead to erroneous conclusions, standardized field methods, the calculation of local correction factors at sites where adequate data are available, or the use of our general standardizing formula to take account of sample intervals, are to be recommended.
Nutrient limitation of plant growth and forage quality in Arctic coastal marshes
Authors: NGAI JACQUELINE T. , JEFFERIES ROBERT L.
Published: December 2004

Foraging by geese has led to vegetation loss in salt marshes along the Hudson Bay coast and lesser snow geese are increasingly grazing inland freshwater marshes. We determined whether different nutrients limit the growth of forage plants in the two habitats, and whether these differences affect the nutritional quality of vegetation available to geese at La Pérouse Bay, Manitoba.

Results from fertilization experiments indicate that primary productivity in the salt marsh is both nitrogen and phosphorus limited, whereas the freshwater marsh is phosphorus limited. Total amounts of calcium, magnesium and potassium in above‐ground biomass per unit area showed similar differences in limitation.

Leaves of preferred forage species have higher nutrient concentrations (nitrogen, phosphorus, calcium, potassium, magnesium, sodium) and lower C : N and C : P ratios than alternative forage. The main forage species in the salt marsh (Puccinellia phryganodes) has higher nutrient content per unit mass, for nitrogen, magnesium, calcium and sodium, than the major freshwater marsh species(Carex aquatilis). The difference in nutritional quality of forage between the marshes is likely to have had consequences for goose fitness, and may have contributed to the reported declines in gosling survivorship and size.

At moderate grazing intensities, seasonal growth of salt‐marsh forage is maintained by addition of nitrogen and, to a lesser extent, phosphorus from high numbers of goose faeces to swards. In contrast, the low densities and low phosphorus content of goose faeces in the phosphorus‐limited freshwater marsh mean that plants are unlikely to recover rapidly from the effects of grazing. As a consequence, the freshwater marsh is likely to become increasingly less productive as foraging intensifies.

Nutrient gradients in vegetation across an ecotone and changes in foraging behaviour have resulted in adverse effects on both the growth rates of individuals and the population structure of a herbivore.
Regulation of anti‐herbivore defence by Fucus vesiculosus in response to various cues
Authors: ROHDE SVEN , MOLIS MARKUS , WAHL MARTIN
Published: December 2004

We examined whether the marine macroalga Fucus vesiculosus induces defences against herbivory and, if so, which factors trigger this induction. In addition, we assessed whether induced defences are reduced after consumption stops.

Induced effects were measured as changes in palatability rather than changes in the chemistry of the algae. We also tested for reductions in growth rate to determine whether induced defence incurs metabolic costs.

We tested whether direct grazing, feeding on neighbouring plants, clipping and presence of a non‐grazing herbivore could trigger induction. The isopod Idotea baltica and the gastropod Littorina littorea were used as herbivores.

Both direct feeding of I. baltica and feeding on neighbouring plants induced chemical defence in F. vesiculosus, whereas the snail L. littorea only induced defence by direct grazing. Simulated herbivory (clipping), or the presence of herbivores without grazing, did not lead to defence induction. All induced defences were reversed within 2 weeks of consumption ending.

Thus, F. vesiculosus differentiates between physical damage and natural herbivory. Furthermore, feeding by I. baltica on F. vesiculosus releases signals that trigger neighbouring Fucus individuals to induce defence.

We found no evidence that metabolic costs incurred as a consequence of induced defence were sufficient to lead to growth reduction.

This algal species demonstrates defence plasticity (i.e. induction and reduction of anti‐herbivore defences ‘on demand’), with the response depending on both grazer identity and grazing pattern matter.
Leaf area and growth of juvenile temperate evergreens in low light: species of contrasting shade tolerance change rank during ontogeny
Authors: LUSK C. H.
Published: December 2004

Interspecific variation in leaf life span of woody plants should have important consequences for ontogenetic variation in biomass distribution, and hence carbon balance, in low light. This proposal was examined by measuring foliage turnover, growth, biomass allocation and biomass distribution of juveniles (25–1180 mm tall) of four evergreens differing in shade tolerance, growing in low light (2–5% canopy openness) in temperate rainforest understoreys in south‐central Chile.

As predicted, ontogenetic trends in leaf area ratio (LAR) of two very shade‐tolerant species with long‐lived leaves (Aextoxicon punctatum and Myrceugenia planipes) contrasted strongly with those of mid‐tolerant Eucryphia cordifolia and intolerant Aristotelia chilensis. Low‐light LAR fell rapidly with increasing plant size in Eucryphia and Aristotelia, but was size‐invariant in the two shade‐tolerant taxa. As a result, although small seedlings of Eucryphia and Aristotelia displayed more leaf area than shade‐tolerant seedlings of similar size (largely because of differences in specific leaf area), this relationship was reversed for plants over ≈500 mm tall.

Although the slower foliage turnover of the shade‐tolerant species at least partly explains this reversal, allocational differences may also be involved. Root mass fraction of both shade‐tolerant species was significantly negatively correlated with size, possibly reflecting declining allocation to roots in larger plants. In contrast, root mass fraction was not correlated with size in Eucryphia or Aristotelia.

Above‐ground relative growth rate in low light followed similar ontogenetic trends to LAR, declining more quickly in light‐demanding species than in shade‐tolerant associates. As a result, large seedlings (>400 mm tall) of shade‐tolerant Myrceugenia and Aextoxicon grew more quickly than their light‐demanding associates at the same height. The steeply declining LAR and growth of Eucryphia and Aristotelia suggest that these taxa will eventually die of energy starvation in low light.

Results are consistent with the idea that accumulation of an extensive leaf area eventually gives juvenile shade‐tolerant evergreens a net carbon gain advantage over their light‐demanding associates in low light. Awareness of long‐term ontogenetic trends will enhance understanding of relationships of shade‐tolerance variation with morphology and growth of woody evergreens.
Sprouting by plants: the effects of modular organization
Authors: VESK P. A. , WESTOBY M.
Published: December 2004

Plant survival following disturbance was modelled simply as the probability that at least one of n stems sprouts, each stem having an independent probability of sprouting, s. This first‐order model with any stem on any plant in any species having probability s = 0·18 of sprouting after clipping (s = 0·09 after burning) explained nearly half of the deviance associated with species’ mortality in a field experiment on 43 species from a range of growth forms.

Allowing species to take either a low or high per‐stem sprouting probability (SSP) improved statistical explanation substantially. Fitting growth form SSP was less effective, showing that much of the apparent among‐species variation in SSP was within growth forms.

Allowing each species to have a different SSP essentially provided a saturated model. The estimated species‐specific probabilities were positively related to the depth from which sprouts could emerge after disturbance. Predicting species’ bud depth from some simply measured morphological trait would be a considerable advance. Limited evidence suggested that sprout depth was associated with thick or dense leaves (low specific leaf area and leaf water content).

Depicting plants as a collection of independent stems with equal probability of sprouting appears a reasonable first‐order model for whole‐plant sprouting, despite being morphologically simplified.
Leaf digestibility and litter decomposability are related in a wide range of subarctic plant species and types
Authors: CORNELISSEN J. H. C. , QUESTED H. M. , GWYNN‐JONES D. , VAN LOGTESTIJN R. S. P. , DE BEUS M. A. H. , KONDRATCHUK A. , CALLAGHAN T. V. , AERTS R.
Published: December 2004

Herbivory and litter decomposition are key controllers of ecosystem carbon and nutrient cycling. We hypothesized that foliar defences of plant species against vertebrate herbivores would reduce leaf digestibility and would subsequently, through ‘afterlife effects’, reduce litter decomposability.

We tested this hypothesis by screening 32 subarctic plant species, belonging to eight types in terms of life form and nutrient economy strategy, for (1) leaf digestibility in cow rumen juice; (2) biochemical and structural traits that might explain variation in digestibility; and (3) litter mass loss during simultaneous incubation in an outdoor subarctic litter bed.

Interspecific variation in green‐leaf digestibility corresponded significantly with that in litter decomposability; this relationship was strongly driven by overall variation among the eight plant types (r = 0·92). The same relationship was not detectable within plant types in taxonomic relatedness tests.

Several biochemical and structural parameters (phenol‐to‐N ratio, lignin‐to‐N ratio) explained a significant part of the variation in leaf digestibility, but again only between and not within plant types.

Our results provide further support for the role played by foliar defence in the link between plant and soil via the decomposition pathway. They are also a new example of the potential control of plant functional types over carbon and nutrient dynamics in ecosystems.
Environmental severity and variation in the reproductive traits of Impatiens glandulifera
Authors: WILLIS S. G. , HULME P. E.
Published: December 2004

Seed mass is widely regarded as a key plant trait, yet is notoriously variable within an individual species. This study reports the first field experiments to disentangle the relative importance of four major correlates of seed mass variation: resource limitation; plant height; seed number; and seasonality.

Variation in reproductive traits in Impatiens glandulifera Royle was partitioned among six populations established across an elevation gradient, among plants at each elevation and within individual plants.

Seed mass was the least variable trait both at the individual and population levels, while the number of pods per plant varied most. Seed mass variation was greatest among individual plants (42%) and was least among populations (28%).

Taller plants produced proportionally more seed pods and more seeds per pod. Seed mass was not related to the number of pods per plant, or the number of seeds per pod. Thus with increasing resources, I. glandulifera allocated resources to produce more seeds rather than larger seeds.

Seed mass was negatively correlated with the heat sum over the period of seed maturation, explaining increased seed mass at higher elevations and increasing seed mass over time at most elevations. This may indicate that environmental condition pre‐ and post‐fertilization determines the relationship between seed mass and elevation, thereby limiting the potential for evolutionary selection for seed‐size optima.

The study warns against correlative studies of seed mass variation that select arbitrary populations or ignore the temporal dynamics in seed mass, as these may generate spurious correlations among life‐history traits.

The success of I. glandulifera as an invasive species may reflect the extended period of seed release, considerable seed mass variation and large seed size under conditions of environmental severity. These traits will facilitate the exploitation of spatially and temporally heterogeneous natural environments commonly found in riparian ecosystems.
Body size and mating strategies in the simultaneous hermaphroditeOxynoe olivacea(Mollusca, Opisthobranchia, Sacoglossa)
Authors: GIANGUZZA P. , BADALAMENTI F. , JENSEN K. R. , CHEMELLO R. , CANNICCI S. , RIGGIO S.
Published: December 2004

To better understand the role and importance of body size in hermaphroditic mating system theory, the mating behaviour of the shelled sacoglossanOxynoe olivaceawas studied. This simultaneous hermaphrodite exhibits bilateral and unilateral sperm transfer and thus it is particularly suitable for studies on hermaphrodite sexual conflict.

In this study three hypotheses on body size were tested: thatO. olivaceapartner size has an effect on (i) mating mode choice, (ii) duration of mating modes, and (iii) choice of sexual role. Furthermore, we tested Charnov's hypothesis that inO. olivacea, like many simultaneous hermaphrodites, a sexual conflict exists and the male role is preferred.

A laboratory experiment was done to test the aforementioned hypothesis and to observe the general mating behaviour ofO. olivacea. Pairs of similar (S) and different (D) sizes were considered for a total of five different treatments (S1, S2, S3, D1, D2).

During the five copulatory treatmentsO. olivaceamated up to 93 times. Specifically, pairs of the same size mated with bilateral sperm transfer while unilateral copulation was common in pairs of slightly differing size. Contrary to predictions, animals of small body size started mating in the female role.O. olivaceashowed an active alternation of sexual roles and thus did not specialize in one particular sexual role.

This study produced evidence of a relationship between mating mode and body size inO. olivaceaand highlighted the need for new studies on this simultaneously hermaphroditic species.
Aerodynamics of wind pollination in a zoophilous flower, Brassica napus
Authors: CRESSWELL J. E. , DAVIES T. W. , PATRICK M. A. , RUSSELL F. , PENNEL C. , VICOT M. , LAHOUBI M.
Published: December 2004

The flower of Brassica napus L. appears to be typically zoophilous (suited to animal pollination) because of its visually attractive petals, robust stigma and nectaries. Pollination by wind is feasible, however, and its likely effectiveness is not immediately foreseeable because of the complexity of interactions between objects and windborne particles.

Computational fluid dynamics (CFD) and wind‐tunnel experiments were used to investigate the aerodynamic interactions between the flower and a windborne suspension of its pollen.

The flower's petals handicapped wind pollination by reducing the target efficiency of the upwind‐facing stigma. For downwind‐facing flowers, pollen reception was negligible.

Several aspects of the plant's architecture (floral structure, pollen cohesiveness, inflorescence structure) are uncompromisingly zoophilous. Estimates of the amount of wind pollination suggest that it is unlikely to be important for the long‐distance dispersal of B. napus genes such as those from genetically modified varieties.

This study illustrates how CFD may become a powerful tool in future analyses of wind pollination.
Respiration and thermogenesis by cones of the Australian cycad Macrozamia machinii
Authors: SEYMOUR R. S. , TERRY I. , ROEMER R. B.
Published: December 2004

While cycads are often considered to be wind‐pollinated, it is now clear that insects are pollen vectors in many species. This study addresses the role of thermogenesis in pollination biology of the dioecious cycad Macrozamia machinii P.I. Forster & D.L. Jones.

The patterns of thermogenesis in intact male and female cones were assessed with thermometry and respirometry throughout the pollination period in the field.

Thermogenic episodes in male cones occurred from about 17.00–00.00 h on successive evenings, in association with dehiscence of sporangia and presence of their pollinating weevils (Tranes sp.).

Temperatures of the 167 g male cones rose ≈6 °C above ambient, and mean rate of oxygen consumption peaked at 7·7 µmol s−1 (3·6 W). Regulation of male cone temperature was not evident, and thermogenesis of female cones was insignificant.

Male cones probably heat to augment scent production and enhance weevil activity, including mating and egg‐laying, but female cones may benefit from reduced visitation and freedom from damage by weevil larvae. Male cones may be sacrificial in providing the reward to the pollinators while the female cones are safeguarded.
Comparing foraging behaviour of small and large honey‐bee colonies by decoding waggle dances made by foragers
Authors: BEEKMAN M. , SUMPTER D. J. T. , SERAPHIDES N. , RATNIEKS F. L. W.
Published: December 2004

We compared the foraging behaviour of two small (approximately 6000 bees) and two large (approximately 20 000 bees) honey‐bee colonies over 6 days. We determined where the bees of each colony foraged, whether they collected nectar or pollen, the number of patches foraged at, the number of bees engaged in foraging, and the concentration of the nectar collected.

Even though the colonies were located in the same environment and had the same genetic background, foragers from different colonies used different forage patches.

Small and large colonies foraged at a similar distance in July when forage was abundant (mean foraging distance for small and large colonies was 0·67 and 0·62 km, respectively) whereas the large colonies foraged significantly further in August when forage was scarce (mean foraging distance for small and large colonies was 1·43 and 2·85 km, respectively).

Small colonies foraged at approximately the same number of patches as large colonies. The total number of foragers returning to the small colonies per minute was significantly lower than the number of foragers returning to the large colonies. This means that, relative to their size, small colonies foraged at more patches than large colonies.

The quality of the nectar collected by foragers of the small and large colonies did not differ. However, small colonies did collect more pollen than large colonies.
Long‐term canopy dynamics in a large area of temperate old‐growth beech (Fagus crenata) forest: analysis by aerial photographs and digital elevation models
Authors: HENBO YUKO , ITAYA AKEMI , NISHIMURA NAOYUKI , YAMAMOTO SHIN‐ICHI
Published: December 2004

Long‐term canopy dynamics in a large area of temperate old‐growth beech forest in the Daisen Forest Reserve, south‐western Japan (11.56 ha studied over 43 years), were investigated using digital elevation models (DEMs) of the canopy surface, constructed from aerial photographs taken in the growing season (i.e. with foliage) in 1958, 1978, 1992 and 2001. A ground surface DEM at the same resolution (a 2.5 × 2.5 m grid) was constructed using aerial photographs taken when foliage was absent (winter 2002). Canopy height data were obtained by calculating differences in elevation between the canopy and the ground surface, and a canopy height profile was constructed.

Topographic data for a 4‐ha plot, located within the 11.56‐ha area, were obtained via a ground survey and used to validate the ground surface DEM derived from aerial photographs.

Canopy height class distributions changed significantly over the 43 years. The total number of gaps, defined as areas where canopy height was ≤ 15 m, decreased but total gap area increased over time. Total gap area in 2001 was twice that of 1958. The density of gaps decreased as gap size increased.

Gap formation rates increased from 0.47% year−1 (1958–78) to 1.30% year−1 (1992–2001), with a mean of 0.77% year−1, and substantially exceeded closure rates, which fluctuated from 0.28% year−1 (1958–78) to 0.54% year−1 (1978–92), with a mean of 0.39% year−1. Gaps generally expanded and became connected to each other.

Temporal variation in gap formation and closure might be correlated with the frequency and severity of typhoon disturbances but, if the observed trends continue, this old‐growth beech stand may become an open stand. The long‐term dynamics of this forest type appear to be far from equilibrium.
Novel phenotypes among early generation hybrids of two Louisiana iris species: flooding experiments
Authors: JOHNSTON JILL A. , DONOVAN LISA A. , ARNOLD MICHAEL L.
Published: December 2004

Recent studies of hybridization have shown that extreme (e.g. transgressive) phenotypes can be generated during massive genetic recombination events such as interspecific hybridization. Extreme hybrid phenotypes appear to have the potential to create new lineages and lead to evolutionary divergence.

Hybrid genotypes of some salt marsh species have proven capable of reengineering their ecosystems, while in other cases, hybridization has transformed plant communities by facilitating species invasion.

Using the Louisiana irises, a naturally hybridizing group of species, we assessed the potential for hybrids ofIris brevicaulisandI. fulvato possess extreme physiological and growth traits. Our glasshouse experiment used two soil water environments (wet and flood) to measure hybrid trait expression at both the genotypic class and individual genotype level.

At the genotypic class level, two of the three hybrid classes (F1s, and backcrosses towards each parental species) were transgressive for at least one physiological trait (F1s for root mass proportion, specific leaf area and final leaf area; backcrosses toI. brevicaulisfor leaf area ratio). Three fitness components (total biomass, ramet production and flower production) were measured on each plant in the experiment. All three hybrid classes had greater clonal fitness (total biomass) but not greater sexual fitness (flower number) than parent species.

At the individual genotype level, two F1hybrids showed extreme physiological trait expression: one for specific leaf area, and the other for shallow root allocation. Flower production was the only fitness component that showed some degree of environment‐dependence at the individual genotype level.

Although early generation hybrid classes can contain rare genotypes with extreme phenotypic trait expression, and hybrid fitness components were equal or superior to both parental species in most cases, there was not a strong association between transgressive traits and elevated hybrid fitness.
Factors predisposing episodic drought‐induced tree mortality in Nothofagus– site, climatic sensitivity and growth trends
Authors: SUAREZ MARIA LAURA , GHERMANDI LUCIANA , KITZBERGER THOMAS
Published: December 2004

Although climatic variability is a strong driving force for forest dynamics, drought‐induced mortality has generally received much less attention than other types of disturbance.

In 1998–99 northern Patagonia was affected by one of the most severe droughts of the 20th century, coinciding with a strong La Nina event, and this caused high mortality of Nothofagus dombeyi (coihue), the dominant tree species in Nahuel Huapi National Park.

Factors involved in determining this mortality of N. dombeyi were examined at both patch and tree level. Radial growth characteristics of killed trees and survivors were compared by dendrochronological analyses. Relationships between growth and climate were investigated using response function analysis.

At the tree scale, individuals with variable growth were more prone to die from drought than trees with more regular growth. Juveniles whose growth patterns showed sensitivity to climate were particularly likely to die. However, among both killed trees and survivors, older trees were less sensitive to climate.

Mean growth rate was a good predictor of mortality in adult trees, showing that trees with slower growth rate were more susceptible to drought. Susceptible trees may have been negatively affected by the drought that affected northern Patagonia in 1956–57.

These results underscore the importance of considering drought‐induced tree mortality as a non‐random mechanism influenced by site, previous stress/disturbance history, ontogeny, vigour, climatic sensitivity and physiology. Spatial patterns of extensive full and partial crown dieback, which are evident in many temperate forests worldwide, may reflect the superposition of these predisposing factors on strong/repeated interannual fluctuations of climate.
Plasma terminal half‐life
Authors: TOUTAIN P. L. , BOUSQUET‐MÉLOU A.
Published: December 2004

Terminal plasma half‐life is the time required to divide the plasma concentration by two after reaching pseudo‐equilibrium, and not the time required to eliminate half the administered dose. When the process of absorption is not a limiting factor, half‐life is a hybrid parameter controlled by plasma clearance and extent of distribution. In contrast, when the process of absorption is a limiting factor, the terminal half‐life reflects rate and extent of absorption and not the elimination process (flip‐flop pharmacokinetics). The terminal half‐life is especially relevant to multiple dosing regimens, because it controls the degree of drug accumulation, concentration fluctuations and the time taken to reach equilibrium.
Pharmacokinetics and pharmacokinetic/pharmacodynamic relationships for angiotensin‐converting enzyme inhibitors
Authors: TOUTAIN P. L. , LEFÈBVRE H. P.
Published: December 2004

The pharmacokinetic (PK) properties and the pharmacokinetic/pharmacodynamic (PK/PD) relationships for the angiotensin‐converting enzyme (ACE) inhibitors (ACEIs), such as enalaprilat, benazeprilat, imidaprilat and ramiprilat, differ from those of conventional drugs. This is because of their immediate and saturable binding to an ACE pool which is partly circulating (and contributing to the measured plasma concentration), and partly noncirculating (tissular), being anchored to the endothelium of vessels and not measurable by the analytical technique. A physiologically based model is required to allow appropriate interpretation of the different phases of the disposition curve of ACEI. The protracted terminal phase observed for all ACEIs is not a conventional elimination phase but a phase dependent on ACEI dissociation from ACE. In contrast, the phase which reflects ACEI elimination (and which is interpreted as a distribution phase for a conventional drug) has a short half‐life, thus explaining the absence of drug accumulation during repeated dosing and mild kidney failure. ACE inhibition is the surrogate endpoint generally selected for establishing a PK/PD relationship and for simulating dosage regimen scenarios in order to decide on the appropriate dosage regimen for ACEIs.
Volumes of distribution
Authors: TOUTAIN P. L. , BOUSQUET‐MÉLOU A.
Published: December 2004

Volumes of distribution are proportionality constants between total amount of drug in the body and plasma concentrations. As snapshot plasma drug concentrations may be measured in different conditions (at equilibrium, under pseudo‐equilibrium condition,…), several volumes of distribution have been defined. The two most relevant are the volume of distribution at equilibrium (Vss), and the volume of distribution during pseudo‐equilibrium (Varea). Volumes of distribution are used to compute a loading dose (Vss) or the residual amount of drug in the body knowing plasma concentrations (Varea). Volume of distribution may be interpreted in terms of drug distribution having recourse to physiological models involving drug binding to plasma and tissues. Volumes of distribution should be determined early in drug development programmes and those having a large volume of distribution may be selected to obtain a long terminal half‐life even for drugs having a relatively high clearance.