bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting iterative time reversal processing: Application to detection of multiple targets
Authors: Montaldo Gabriel , Tanter Mickaël , Fink Mathias
Published: February 2004

The iterative time reversal processing represents a high speed and easy way to self-focus on the strongest scatterer in a multitarget medium. However, finding weaker scatterers is a more difficult task that can be solved by computing the eigenvalue and eigenvector decomposition of the time reversal operator, the so-called DORT method. Nevertheless, as it requires the measurement of the complete interelements response matrix and time-consuming computation, the separation of multiple targets may not be achieved in real time. In this study, a new real time technique is proposed for multitarget selective focusing that does not require the experimental acquisition of the time reversal operator. This technique achieves the operator decomposition using a particular sequence of filtered waves propagation instead of computational power. Due to its simplicity of implementation, this iterative process can be achieved in real time. This high speed selective focusing is experimentally demonstrated by detecting targets through a heterogeneous medium and in a speckle environment. A theoretical analysis compares this technique to the DORT formalism.
A molecular description of profile analysis: Decision weights and internal noise
Authors: Berg Bruce G.
Published: February 2004

Systematic inefficiencies and internal noise in a spectral profile discrimination task were investigated. Listeners detected a 1000-Hz sinusoid added in-phase to the central component of a complex consisting of 11 equal-intensity sinusoids. Parameters for a channel model that employs decision weights and internal noise were estimated with molecular psychophysical techniques. Maximum likelihood predictions of the model were generally within a few decibels of observed thresholds. The degree to which an assumption of ideal weights leads to overestimation of internal noise was also assessed.
The effects of membrane metallization in capacitive microfabricated ultrasonic transducers
Authors: Caronti Alessandro , Carotenuto Riccardo , Caliano Giosuè , Pappalardo Massimo
Published: February 2004

The mechanical effects of the metal layer on the membranes of capacitive micromachined ultrasonic transducers (CMUTs) are analyzed in this paper by means of finite element simulations. The influence of electrode size and thickness on the electrostatic behavior of the single CMUT cell, including diaphragm displacement, cell capacitance, and collapse voltage, is explored. The effect on device sensitivity is investigated through the transformation factor of the cell, that is computed by FEM and compared with the parallel plate model prediction. It is found that for a non-negligible electrode thickness, as in the majority of fabricated devices, both the static and dynamic performance of the cell can be affected in a significant way. Thus, the effects of membrane metallization must be taken into account in CMUT design and optimization.
Beneficial effects of direct foliar water uptake on shoot water potential of five chasmophytes
Authors: Gouvra E , Grammatikopoulos G
Published: January 2004

Five chasmophytic species growing as wall-fissure plants on vertical retaining walls of a castle in the town of Patras, Greece, were examined for their ability to benefit from direct absorption of foliar surface water. Epifluore scence microscopy and application of an apoplastic tracer of water movement indicated that sprayed water on leaf surfaces penetrated into the mesophyll of all species, and in some cases was also detected within conducting tissues of the leaf. Water potential (Ψw) of sprayed detached shoots was improved compared with unsprayed controls when they were slowly losing water under laboratory conditions. The beneficial effect of leaf water absorption on Ψw was found either on leaves that were originally fully turgid or on leaves that had undergone a considerable water content reduction. Sprayed leaves maintained their Ψw above turgor loss point for a time period of 10-90 min depending on species and degree of water deficiency. The relevance of the results to the importance of dew uptake from chasmophytes growing under water shortage in wall fissures in inhabited areas is discussed.Key words: chasmophytes, leaf water absorption, wall vegetation, drought resistance.
Use of architectural and morphometric analysis to predict the flowering pattern of the invasiveRubuson Réunion island (Indian Ocean)
Authors: Baret Stéphane , Nicolini Eric , Humeau Laurence , Bourgeois Thomas Le , Strasberg Dominique
Published: January 2004

The inability to flower and produce fruit above 1100 m a.s.l. is an important characteristic of Rubus alcei folius Poiret (Rosaceae), an introduced bramble that has invaded large areas of tropical rain forest on Réunion island. Why does R. alceifolius not fruit in the highlands? It is known that a minimal morphological structure and structural maturity level is required for plants to reach the reproductive state. In this study, we explored the threshold of this minimal morphological structure by describing mesotonic and basitonic axes at two different altitudes. All measured axes remained vegetative, except those that fruited in the lowlands. The morphological factors noted in R. alceifolius enabled us to define the minimum structure required for fruiting in lowland areas. Mesotonic axes seem to achieve structural maturity in the highlands, but the reproductive state did not occur. Our results may be helpful for eradication and biocontrol programs that depend strongly on the reproductive strategy of the target invasive plant species.Key words: altitude, metamer, minimum structure, pith, reproductive state, Rubus alceifolius.
The ability of ectomycorrhizal fungi to utilize fatty acids and a lipid as a carbon source for mycelial growth
Authors: Hattori Takefumi , Ohta Akira , Itaya Masayuki , Shimada Mikio
Published: January 2004

We have investigated growth of ectomycorrhizal (ECM) fungi (i.e., 55 strains of 32 species in 15 genera) on saturated (palmitate), monounsaturated (oleate), diunsaturated (linoleate), triunsaturated (linolenate) fatty acids, and the triacylglyceride of oleate (triolein) lipid to elucidate an ability to utilize the fatty acids and lipid as a carbon source for growth. Relative utilization ratios (URs, %) based on mycelial growth on glucose suggest that ECM fungi belonging to the family Thelephoraceae have an ability to utilize palmitate. On the other hand, ECM fungi in the genus Laccaria can utilize at least either palmitate or oleate. Furthermore, Hygropharus russula grows on palmitate, oleate, and slightly on triolein. Lactarius chrysorrheus grows only on palmitate. These fatty-acid- and lipid-utilizing fungi may be promising as model fungi for further elucidation of the metabolic ability to utilize the fatty acids and lipid as a carbon source. On the contrary, the fungi in the genus Suillus were shown to scarcely utilize the fatty acids and lipid. Furthermore, most ECM fungi did not grow on either linoleate or linolenate.Key words: carbon source, ectomycorrhizal fungi, fatty acid, lipid, mycelial growth.
Cold-adapted rhizobia for nitrogen fixation in temperate regions
Authors: Prévost Danielle , Drouin Pascal , Laberge Serge , Bertrand Annick , Cloutier Jean , Lévesque Gabriel
Published: January 2004

Rhizobia from Canadian soils were selected for cold adaptation with the aim of improving productivity of legumes that are subjected to cool temperatures during the growing season. One approach was to use rhizobia associated with legume species indigenous to arctic and subarctic regions: (i) Mesorhizobium sp. isolated from Astragalus and Oxytropis spp. and (ii) Rhizobium leguminosarum from Lathryrus spp. The majority of these rhizobia are considered psychrotrophs because they can grow at 0 °C. The advantages of cold adaptation of arctic Mesorhizobium to improve legume symbiosis were demonstrated with the temperate forage legume sainfoin (Onobrychis viciifolia). In laboratory and field studies, arctic rhizobia were more efficient than temperate (commercial) rhizobia in improving growth of sainfoin and were more competitive in forming nodules. Biochemical studies on cold adaptation showed higher synthesis of cold shock proteins in cold-adapted than in nonadapted arctic rhizobia. Since arctic Mesorhizobium cannot nodulate agronomically important legumes, the nodulation genes and the bacterial signals (Nod factors) were characterized as a first step to modifying the host specificity of nodulation. Another valuable approach was to screen for cold adaptation, that is, rhizobia naturally associated with agronomic legumes cultivated in temperate areas. A superior strain of Sinorhizobium meliloti adapted for nodulation of alfalfa at low temperatures was selected and was the most efficient for improving growth of alfalfa in laboratory and field studies. This strain also performed well in improving regrowth of alfalfa after overwintering under cold and anaerobic (ice encasement) stresses, indicating a possible cross-adaptation of selected rhizobia for various abiotic stresses inherent to temperate climates.Key words: cold adaptation, legumes, symbiotic efficiency, cold shock protein, nodulation genes, anaerobiosis.
Genetic analysis of the expression of the cold-regulated gene cor14b: a way toward the identification of components of the cold response signal transduction in Triticeae
Authors: Crosatti C , Marè C , Mazzucotelli E , Belloni S , Barilli S , Bassi R , Dubcovskyi J , Galiba G , Stanca A M , Cattivelli L
Published: January 2004

Extensive molecular biological studies have led to the cloning of many cold-regulated genes (cor) whose expression is up-regulated in winter cereals during exposure to cold. Among them is cor14b, a nuclear gene coding for a chloroplast-localized protein whose expression level has been associated with frost resistance in Triticeae. Although frost tolerance is recognised as a complex quantitative character, members of homologous group 5 in Triticeae are known to carry major loci determining frost tolerance. In this work we summarize a number of recent experiments where the cold-regulated gene cor14b was used as a tool (i) to understand the genetic relationship between the expression of cor genes and the frost resistance loci and (ii) to identify barley mutants revealing a chloroplast role in the signal transduction pathway leading to the molecular cold response.Key words: Triticeae, cold hardening, frost resistance, cor genes.
Transcriptional responses to low temperature and their regulation in Arabidopsis
Authors: Zhu Tong , Provart Nicholas J
Published: January 2004

Recent studies have used a transcriptional profiling approach to identify genes in Arabidopsis that respond at the level of transcript abundance to cold (4 °C) or chilling (13 °C) temperatures. Results have shown that plants respond to low temperatures by altering mRNA levels of a large number of genes belonging to different independent pathways. Early transcriptional response to low temperatures frequently involves signaling pathways used to respond to other environmental stresses, indicating the existence and involvement of a complex genetic network. Genes with functions specific to low-temperature signaling pathways, and those with functions in multiple signaling pathways, especially those encoding transcription factors and other signaling molecules, have been identified based on their transcriptional responses to different environmental stresses. The qualitative and quantitative difference in transcriptional response to chilling and cold suggests that plants might have different molecular mechanisms to acclimate to different types of low-temperature stresses. The regulation and interactions of genes involved in low-temperature response at the transcriptional level has been further explored by computational methods, and preliminary results have identified motifs that are known to be important for cold response, raising the possibility of a better understanding of the processes involved.Key words: Arabidopsis, low-temperature stress, gene expression, transcriptional regulation, microarray.
Vegetative storage proteins in overwintering storage organs of forage legumes: roles and regulation
Authors: Avice J -C , Dily F Le , Goulas E , Noquet C , Meuriot F , Volenec J J , Cunningham S M , Sors T G , Dhont C , Castonguay Y. , Nadeau P , Bélanger G , Chalifour F -P , Ourry A
Published: January 2004

In perennial forage legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.), vegetative storage proteins are extensively mobilized to meet the nitrogen requirements of new shoot growth in spring or after cutting in summer. The 32-kDa alfalfa storage protein possesses high homology with class III chitinases, belonging to a group of pathogenesis-related proteins that possess antifreeze protein properties in some species and exhibit chitinolytic activity in vitro. This protein and the corresponding mRNA accumulate in taproots of cold-hardy culti vars during acclimation for winter, and in response to short-day conditions in controlled environments. The 17.3-kDa storage protein of white clover possesses high homology with pathogenesis-related proteins and abscisic- acid-responsive proteins from several legume species and has characteristics common to stress-responsive proteins. Low temperature enhances accumulation of this 17.3-kDa protein and its corresponding transcript. Exogenous abscisic acid stimulates the accumulation of vegetative storage proteins and their transcripts in both legume species. These observations suggest that vegetative storage proteins do not exclusively serve as nitrogen reserves during specific phases of legume development, but may play important adaptive roles in plant protection against abiotic (low temperature) and biotic (pathogen attack) stresses.Key words: nitrogen reserves, vegetative storage proteins, regulation, cold tolerance, chitinase, pathogenesis-related proteins.
Plasmodesmata at the crossroads between development, dormancy, and defense
Authors: Rinne Päivi LH , Schoot Christiaan van der
Published: January 2004

Plants are frequently exposed to environmental stress and organisms that seek to benefit from their autotrophic nature. To cope with these challenges plants have developed stress-resistance mechanisms, which involve sensing, activation of signal transduction cascades, changes in gene expression, and physiological adjustment. Exposure to one kind of stress often leads to cross-tolerance, that is, resistance to different kinds of stresses. The search for a common underlying mechanism concentrates mostly on changes in cellular physiology and gene expression. We focus on the cross-protective measures that are taken at the level above the single cell. We argue that the controlled alterations in symplasmic permeability that underlie development also play a role in survival and defense strategies. In development, most of the alterations are transient and dynamic, whereas the more persistent alterations function predominantly in dormancy and defense and are under the control of two key enzymes: 1,3-β-D-glucan synthase and 1,3-β-D-glucanase. 1,3-β-D-Glucan synthase functions in the narrowing or closing of plasmodesmata, whereas 1,3-β-D-glucanase counteracts this process. We propose that the closing of symplasmic paths constitutes an unspecific but effective early measure in adaptation and defense, which is accompanied by specific strategies tailored to the various challenges plants face.Key words: cross-adaptation, dormancy sphincter, 1,3-β-D-glucanase, 1,3-β-D-glucan synthase, meristem, overwintering, plasmodesmata, virus movement.
Freezing tolerance of plants: current understanding and selected emerging concepts
Authors: Guy Charles L
Published: January 2004

The formation of ice on and inside plant tissues represents a major challenge to survival. The resulting phase transition and spatial redistribution of liquid water from inside the cell to extracellular ice results in physical changes to cells and enormous physical stresses and strains. The ability of higher plants to acclimate and tolerate freezing stress is a complex quantitative trait and the product of the activities of not one, but a sizable suite of genes. Many of the known cold-regulated genes are under the control of a primary master regulator, CBF/DREB1, but it is not likely to be the sole master regulator. In considering the origin of freezing tolerance in higher plants, it has been suggested that freezing tolerance likely arose by adopting drought tolerance mechanisms. This may explain why many genes responsive to cold stress are also responsive to drought and (or) other osmotic stresses.Key words: abiotic, dehydration, gene expression, physiology, signal transduction, transcriptome.
Simulation of hybrid forest tree breeding strategies
Authors: Kerr R J , Dieters M J , Tier B , Dungey H S
Published: January 2004

Computer simulation is the only realistic method of evaluating alternative methods of breeding hybrid forest trees. Empirical tests would be very long term and expensive. This paper describes the development of a simulation program, called XSIM, which generates two different but closely related outcrossing tree species. The genetic correlation between performance in each parental species and performance in the resulting hybrid can be set, in addition to the amounts and types of variances in each parental species. The breeding strategies available for testing include conventional reciprocal recurrent selection, reciprocal recurrent selection with forward selection, recurrent selection within each pure species, and the creation of a synthetic species. XSIM allows the strategies to be compared using the same base populations, equivalent selection intensities, and comparable mating patterns. Innovative best linear unbiased prediction procedures allow all ancestral and current progeny generation data, from both parental species and the hybrid, to be analysed together. The theoretical basis for the simulation is given, and genetic and statistical models are described. In summary, XSIM allows rigorous comparisons of the strategies in terms of genetic gain per time and provides useful insight into hybrid forest tree breeding.
Development of an advanced one-dimensional stem heating model for application in surface fires
Authors: Jones Joshua L , Webb Brent W , Jimenez Dan , Reardon James , Butler Bret
Published: January 2004

A new one-dimensional heat conduction model for predicting stem heating during fires is presented. The model makes use of moisture- and temperature-dependent thermal properties for layers of bark and wood. The thermal aspects of the processes of bark swelling, desiccation, and devolatilization are treated in an approximate fashion. An energy balance reveals that simulation with a heat flux input boundary condition requires that these phenomena be accounted for. Previous models have used temperaturetime boundary conditions, which prevents them from being used in conjunction with fire behavior models. This model uses a fluxtime profile for its boundary condition, making it possible to eventually couple it to fire behavior models. The model was developed and validated with laboratory experiments on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) samples. It is intended that this model be used in conjunction with fire behavior and cell mortality models to make predictions of stem heating related mortality before prescribed burns.
Modelling the temporal variation in the seed production of North American trees
Authors: Greene D F , Johnson E A
Published: January 2004

Many aspects of temporal variation in tree seed production (e.g., the proability distribution, periodicity, uni modality) are poorly understood. In this paper, we used 32 annual seed production records from 22 species to show that there are no discernible endogenous cycles, and there is a modest (but seldom significant) tendency for a high seed production year to be followed by an unusually low production year. Finally, we found that all of the records conformed to a single lognormal probability distribution, although our ability to discriminate among species, given short and extremely variable records, is admittedly very limited. We used the lognormal to develop the distribution of the sums of local seed production events (summed across 4 years) as an aid in predicting postharvest or postfire tree regeneration success. Our conclusion is that reliable (defined as 90% of the time) adequate stocking at the edge of an area source requires that the species of interest must comprise a very large fraction of the total basal area per area. Indeed, if the species constitutes less than about 50% of the source, neither burns nor even very narrow strip cuts will be reliably stocked.
Preserving correlation while modelling diameter distributions
Authors: Robinson A
Published: January 2004

The construction of diameter-distribution models sometimes calls for the simultaneous prediction of population parameters from hierarchical data. Appropriate data for such models have characteristics that should be preserved or accommodated: clustering and contemporaneous correlations. Fitting techniques for such data must allow for these characteristics. Using a case study, I compare two techniques  seemingly-unrelated regression (SUR) and principal components analysis (PCA)  whilst using mixed-effects models. I adapt and apply a metric that focuses on volume prediction, which is a key application for diameter distributions. The results suggest that using mixed-effects models provides useful insights into environmental variation, and that SUR is more convenient and produces a slightly better fit than PCA. Both techniques are acceptable with regard to regression assumptions.
Saproxylic beetles (Coleoptera) usingPopulusin boreal aspen stands of western Canada: spatiotemporal variation and conservation of assemblages
Authors: Hammond HE James , Langor David W , Spence John R
Published: January 2004

Saproxylic beetles associated with Populus coarse woody material were sampled from two age classes of fire-origin aspen stands in north-central Alberta, Canada. A combination of rearings from wood bolts and window traps attached to snags yielded 9571 beetles representing 257 taxa over the 3-year period (19931995). We investigated faunal variation across regions, stand ages (mature, 6090 years; old, >100 years), decay classes, wood types, and years in terms of species richness, abundance, and trophic differences. Although trophic structure was similar, faunal composition differed between the two study regions. Species richness and abundance were similar across stand ages; however, many species were collected exclusively or in great majority from old stands and from snags of large diameter, which suggested that truncation of stand age structure through widespread industrial harvest could have serious consequences for saproxylic assemblages. Beetle species richness increased with the level of wood decay, whereas the total catch of beetles tended to be higher in early stages of decay. Wood borer abundance tended to be higher in snags; however, total species richness was higher in logs. Our analyses suggest that (i) many beetle species in the Canadian boreal forest depend directly upon standing and fallen large-diameter woody material from Populus trees, (ii) variation in stage of decay is critical to beetle diversity, and (iii) provision for retention of representative old stands is critical to conservation of saproxylic communities.
Establishment of a cryopreserved gene bank of European elms
Authors: Harvengt L , Meier-Dinkel A , Dumas E , Collin E
Published: January 2004

Cryopreservation of a core collection of 444 elm (Ulmus spp.) clones in liquid nitrogen was carried out by two laboratories participating in a European project of conservation of elm genetic resources. Plant material, collected in nine European countries, represented a large sample of the genetic diversity within three European elm species and their hybrids. The cryopreservation technique used in both laboratories involved the stepwise freezing of cryotubes containing dormant buds. Comparisons with fresh buds showed that the cryopreservation treatment had no negative effect on the viability and regrowth potential of frozen buds. Tests on a random sample of 26 clones showed that direct regrowth of cryopreserved buds (i.e., through propagation by microcuttings) of Ulmus minor and Ulmus laevis was possible; conversely, Ulmus glabra could only be regrown through micrografting. Most thawed explants from all 26 clones survived through the whole cultivation phase and were successfully transferred to the field. A calculation of costs indicates that cryopreservation of elm buds is economically competitive to field clonal archives.
The influence of red alder patches on light, litterfall, and soil nutrients in adjacent conifer stands
Authors: Lavery John M , Comeau Philip G , Prescott Cindy E
Published: January 2004

To evaluate the distance over which red alder patches influence adjacent conifer stands, we measured light transmission and nutrient contents of soil and litterfall along transects crossing the boundary between alder and conifer stands at three sites (1015, 2025, and [Formula: see text]40 years old) in coastal British Columbia. Light levels were higher in the understory of alder stands than in adjacent conifer stands. In simulated openings, light levels rapidly increased with distance from the alder edge, reaching 60% of full sunlight at south-facing edges, 5 m from north-facing edges, and 23 m from east- and west-facing edges. Soil N, NH4-N, NO3-N, and mineralizable N remained elevated for about 10 m from the alder boundary. Nitrogen contents of Douglas-fir seedlings grown in soil from the alder stand were elevated and correlated to soil N concentrations. Nutrient inputs in alder litterfall were positively related to concentrations of total C; total, extractable, and mineralizable N in soils; and the N, P, and B concentrations of seedlings. Alder litterfall drift extended 818 m into adjacent conifer stands. The optimal arrangement for alderconifer mixtures would be alder patches or strips at least 10 m wide and about 20 m apart oriented north to south.
Trends and periodicities in the Canadian Drought Code and their relationships with atmospheric circulation for the southern Canadian boreal forest
Authors: Girardin Martin-Philippe , Tardif Jacques , Flannigan Mike D , Wotton B Mike , Bergeron Yves
Published: January 2004

Trends and periodicities in summer drought severity are investigated on a network of Canadian Drought Code (CDC) monthly average indices extending from central Quebec to western Manitoba and covering the instrumental period 19131998. The relationship and coherency between CDC indices and oceanatmosphere circulation patterns are also examined. Trend analyses indicate that drought severity is unchanged in eastern and central Canada. Composite analyses indicate that for most of the corridor, severe drought seasons occur with a combination of positive 500-hPa geopotential height anomalies centered over the Gulf of Alaska and over the Baffin Bay. Additional severe drought seasons develop across the corridor in the presence of positive height anomalies located over or upstream of the affected regions. According to spectral analyses, the North Atlantic and the North Pacific circulation patterns modulate the drought variability at the decadal scale. Our results lead us to conclude that climate warming and the increases in the amount and frequency of precipitation in eastern Canada during the last century had no significant impact on summer drought severity. It is unlikely that linear climate change contributed to the change in the boreal forest dynamics observed over the past 150 years.
Dynamics of Norway spruce and silver fir natural regeneration in a mixed stand under uneven-aged management
Authors: Grassi Giacomo , Minotta Gianfranco , Tonon Giustino , Bagnaresi Umberto
Published: January 2004

In a 0.75-ha plot in a Norway spruce (Picea abies Karst.)  silver fir (Abies alba Miller) stand in Comelico (Italian eastern Alps), we analysed (i) the distribution and growth of natural regeneration of Norway spruce and silver fir as affected by stand structure and (ii) the age structure of all saplings between 0.2 and 10 m in height in a 30-year-old gap. In both species, most natural regeneration was clumped and located at the margin of the gaps; however, fir saplings were more represented in understorey environments and less represented in gaps as compared with spruce. Age structure of natural regeneration in the selected gap revealed that the majority (75%) of saplings appeared after the formation of the gap; however, for regeneration taller than 2 m (which has a better chance of reaching the uppermost canopy layer), saplings already present at gap formation predominated. We conclude that (i) gap edges represent a preferential regeneration niche in this forest and (ii) saplings established before gap formation can play an important role in gap refilling. These results provide useful information to ensure, through silvicultural practices, favourable conditions for the temporal and spatial continuity of the regeneration process.
Extreme cold temperatures and survival of overwintering and germinated Arceuthobium americanum seeds
Authors: Brandt J P , Hiratsuka Y , Pluth D J
Published: January 2004

Lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) is one of the most damaging pathogens of jack pine (Pinus banksiana Lamb.) in western Canada. Jack pine forests in the colder, more northerly areas, however, are free of dwarf mistletoe, suggesting that the pathogen is limited by low temperature. The effect of extreme cold temperatures on germination rates of overwintering dwarf mistletoe seeds and survival of dwarf mistletoe germinants was evaluated. Germinative ability of overwintering seeds increased with increasing temperatures between 39 and 35 °C, regardless of seed source. Exposure period also strongly influenced germination rates. Exposure to temperatures near 38, 46, or 53 °C for 96 or 144 h was almost always lethal. At 37 °C, germination was greater after 48 h than after 96 h, although it was still significantly lower than in the controls. Temperatures down to 6 °C in late spring did not reduce germinant survival. Overall, these results may explain the absence of dwarf mistletoe from northern areas commonly exposed to periods in winter with minimum temperatures below about 40 °C. These areas are potentially at risk from the pathogen if the climate of Canada's northern interior continues to warm as it has over the last several decades.
Importance of seasonal growth patterns in modelling interactions between radiata pine and some common weed species
Authors: Kimberley Mark O , Richardson Brian
Published: January 2004

Previously described weed competition models that use competition indices based on weed size relative to tree size (e.g., tree height divided by weed height) require models of weed growth and models of weed-free tree growth. A method is presented to model these using standard sigmoidal growth functions and to incorporate regular seasonal patterns of tree growth using Fourier series approximations. The method is tested against data from a field trial at Rotorua, New Zealand, in which Pinus radiata D. Don was grown both on its own and in competition with several common weed species. Weed and tree height were best modelled by a Weibull function, and tree ground line diameter by a Schumacher function. Seasonal fluctuations in both tree and weed growth were adequately modelled by a single-term Fourier series. All weed species showed very similar, strong seasonal fluctuations in height growth, peaking in February. Seasonal fluctuations in tree height growth, and especially diameter growth, were less marked and peaked earlier, in December. Simulations suggested that it is necessary to account for seasonal effects when modelling competition during the first year of growth, but that seasonal effects have less influence in subsequent years.
Random location of fuel treatments in wildland community interfaces: a percolation approach
Authors: Bevers Michael , Omi Philip N , Hof John
Published: January 2004

We explore the use of spatially correlated random treatments to reduce fuels in landscape patterns that appear somewhat natural while forming fully connected fuelbreaks between wildland forests and developed protection zones. From treatment zone maps partitioned into grids of hexagonal forest cells representing potential treatment sites, we selected cells to be treated at random using an algorithm that provides a varying degree of treatment clustering. One thousand or more such maps were used as sample replicates for parameter settings that included landscape size, fraction of area treated, and degree of clustering to test whether continuous fuelbreaks were formed in an acceptable proportion of cases. A shortest path network optimization model was solved for each sample landscape to determine the presence or absence of a continuous fuelbreak and to measure the length of the most direct fuelbreak when one or more were present. By varying the fraction of area treated in a bisection search, we were able to estimate the minimum amount of treatment needed. Results indicated that between 54% and 88% of a forest would need to be treated to form fuelbreaks in 60% or more of the landscapes we modeled.
Characterization of microsatellites revealed by genomic sequencing ofPopulus trichocarpa
Authors: Tuskan Gerald A , Gunter Lee E , Yang Zamin K , Yin TongMing , Sewell Mitchell M , DiFazio Stephen P
Published: January 2004

Microsatellites or simple sequence repeats (SSRs) are highly polymorphic, codominant markers that have great value for the construction of genetic maps, comparative mapping, population genetic surveys, and paternity analyses. Here, we report the development and testing of a set of SSR markers derived from shotgun sequencing from Populus trichocarpa Torr. & A. Gray, a nonenriched genomic DNA library, and bacterial artificial chromosomes. Approximately 23% of the 1536 genomic clones and 48% of the 768 bacterial artificial chromosome subclones contained an SSR. Of the sequences containing an SSR, 72.4% contained a dinucleotide, 19.5% a trinucleotide, and 8.1% a tetranucleotide repeat unit; 26.6% of the sequences contained multiple SSR motifs in a complex or compound repeat structures. A survey of the genome sequence database revealed very similar proportional distribution, indicating that our limited rapid, shallow sequencing effort is representative of genome-wide patterns. In total, 492 primer pairs were designed and these yielded 77 markers that were mapped in an F2pedigree, including 26 that were sufficiently informative to be included in a Populus framework map. SSRs with GC-rich motifs mapped at a significantly higher frequency than expected, although AT-rich SSRs accounted for the majority of mapped markers due to their higher representation in the genome. SSR markers developed from P. trichocarpa showed high utility throughout the genus, with amplification rates in excess of 70% for all Populus species tested. Finally, at least 30% of the markers amplified in several willow species, suggesting that some of these SSRs will be transferable across genera.
ON THE QUINTESSENCE WITH ABELIAN AND NON-ABELIAN SYMMETRY
Authors: LI XIN-ZHOU , HAO JIAN-GANG , LIU DAO-JUN , ZHAI XIANG-HUA
Published: January 2004

We study the perturbations on both "radial" and "angular" components of the quintessence with an internal Abelian and non-Abelian symmetry. The properties of the perturbation on the "radial" component depend on the specific potential of the model and is similiar for both Abelian and non-Abelian case. We show that the cosine-type potential is very interesting for the O (N) quintessence model and also give a critical condition of instability for the potential. While the properties of perturbations on "angular" components depend on whether the internal symmetry is Abelian or non-Abelian, which we have discussed respectively. In the non-Abelian case, the fluctuation of the "angular" component will increase rapidly with time while in the Abelian case it will not.
CREATION OPERATORS FOR TWO-BRANES AND DUALITY IN BF AND CHERN–SIMONS THEORIES IN D=5
Authors: MARINO E. C.
Published: January 2004

We explicitly construct the creation operators for the quantum field configurations associated to quantum membranes (two-branes) in BF and generalized Chern–Simons theories in a space–time of dimension D=5. The creation operators for quantum excitations carrying topological charge are also obtained in the same theories. For the case of D=5 generalized Chern–Simons theory, we show that this operator actually creates an open string with a topological charge at its tip. It is shown that a duality structure exists in general, relating the membrane and topological excitation operators and the corresponding dual algebra is derived. Composite topologically charged membranes are shown to possess generalized statistics that may, in particular, be fermionic. This is the first step for the bosonization procedure in these theories. Potential applications in the full quantization of two-branes is also briefly discussed.
ENERGY AND MOMENTUM DISTRIBUTIONS OF A (2+1)-DIMENSIONAL BLACK HOLE BACKGROUND
Authors: VAGENAS ELIAS C.
Published: January 2004

Using Einstein, Landau–Lifshitz, Papapetrou and Weinberg energy–momentum complexes, we explicitly evaluate the energy and momentum distributions associated with a nonstatic and circularly symmetric three-dimensional space–time. The gravitational background under study is an exact solution of Einstein's equations in the presence of a cosmological constant and a null fluid. It can be regarded as the three-dimensional analogue of the Vaidya metric and represents a nonstatic spinless (2+1)-dimensional black hole with an outflux of null radiation. All four above-mentioned prescriptions give exactly the same energy and momentum distributions for the specific black hole background. Therefore, the results obtained here provide evidence in support of the claim that for a given gravitational background, different energy–momentum complexes can give identical results in three dimensions. Furthermore, in the limit of zero cosmological constant, the results presented here reproduce those obtained by Virbhadra. He utilized the Landau–Lifshitz energy–momentum complex for the same (2+1)-dimensional black hole background in the absence of a cosmological constant.
GLUINO-CONDENSATE (CIV-DV) PREPOTENTIAL FROM ITS WHITHAM–TIME DERIVATIVES
Authors: ITOYAMA H. , MOROZOV A.
Published: January 2004

We describe an expedient way to derive the CIV-DV prepotential in power series expansion in Si. This is based on integrations of equations for its derivatives ∂ℱ/∂Tm with respect to additional (Whitham) moduli Tm. For illustrative purposes, we calculate explicitly the leading terms of the expansion and explicitly check some components of the WDVV equations to the leading order. Extension to any higher order is simple and algorithmic.
FUZZY NAMBU–GOLDSTONE PHYSICS
Authors: BALACHANDRAN A. P. , IMMIRZI G.
Published: January 2004

In space–time dimensions larger than 2, whenever a global symmetry G is spontaneously broken to a subgroup H, and G and H are Lie groups, there are Nambu–Goldstone modes described by fields with values in G/H. In two-dimensional space–times as well, models where fields take values in G/H are of considerable interest even though in that case there is no spontaneous breaking of continuous symmetries. We consider such models when the world sheet is a two-sphere and describe their fuzzy analogs for G = SU (N+1), H = S(U(N-1) ⊗ U (1)) ≃ U(N) and [Formula: see text]. More generally our methods give fuzzy versions of continuum models on S2when the target spaces are Grassmannians and flag manifolds described by (N+1) × (N+1) projectors of rank ≤ (N+1)/2. These fuzzy models are finite-dimensional matrix models which nevertheless retain all the essential continuum topological features like solitonic sectors. They seem well suited for numerical work.
Electric–Magnetic Duality and the Dualized Standard Model
Authors: TSOU Sheung Tsun
Published: January 2004

In these lectures I shall explain how a new-found nonabelian duality can be used to solve some outstanding questions in particle physics. The first lecture introduces the concept of electromagnetic duality and goes on to present its nonabelian generalization in terms of loop space variables. The second lecture discusses certain puzzles that remain with the Standard Model of particle physics, particularly aimed at nonexperts. The third lecture presents a solution to these problems in the form of the Dualized Standard Model, first proposed by Chan and the author, using nonabelian dual symmetry. The fundamental particles exist in three generations, and if this is a manifestation of dual colour symmetry, which by 't Hooft's theorem is necessarily broken, then we have a natural explanation of the generation puzzle, together with tested and testable consequences not only in particle physics, but also in astrophysics, nuclear and atomic physics.

Reported is mainly work done in collaboration with Chan Hong-Mo, and also various parts with Peter Scharbach, Jacqueline Faridani, José Bordes, Jakov Pfaudler, Ricardo Gallego severally.
INVARIANT TENSORS AND DIAGRAMS
Authors: WESTBURY BRUCE
Published: January 2004

In this paper we first give three known examples of strict pivotal categories defined by a finite presentation. Then in the final section we give some of the relations for a conjectural strict pivotal category. If this category can be constructed it gives a ribbon category which specialises to the category of representations of the quantised enveloping algebra of a simple Lie algebra for any simple Lie algebra. This is the quantum group version of the universal Lie algebra introduced in [52] (available on his home web page).
Geometrical measurements in three-dimensional quantum gravity
Authors: Barrett John W.
Published: January 2004

A set of observables is described for the topological quantum field theory which describes quantum gravity in three space-time dimensions with positive signature and positive cosmological constant. The simplest examples measure the distances between points, giving spectra and probabilities which have a geometrical interpretation. The observables are related to the evaluation of relativistic spin networks by a Fourier transform.
HOMOTOPY QUANTUM FIELD THEORIES AND RELATED IDEAS
Authors: BRIGHTWELL MARK , TURNER PAUL , WILLERTON SIMON
Published: January 2004

In this short note we provide a review of some developments in the area of homotopy quantum field theories, loosely based on a talk given by the second author at the Xth Oporto Meeting on Geometry, Topology and Physics.
REGIONAL FISHERIES MANAGEMENT ON THE HIGH SEAS: THE HIT-AND-RUN INTERLOPER MODEL
Authors: MCKELVEY ROBERT W. , SANDAL LEIF K. , STEINSHAMN STEIN I.
Published: January 2004

The 1993 U.N. Straddling Stock Agreement prescribes a multi-national organizational structure for management of an exploited marine fish stock, one whose range straddles both "Extended Economic Zones" (EEZs) and high seas waters. However, the Agreement provides to the Regional Organization no coercive enforcement powers. In this connections two problems in particular have been cited: The first, called the "interloper problem", concerns the difficulty of controlling the harvesting by non-member vessels. The second problem, called the "new-member problem", concerns the inherent difficulties of negotiating mutually acceptable terms of entry.

Here we explore the extent to which the coalition, by exerting economic power alone, might be able to attain effective leverage in these management-control controversies. Specifically, we will examine whether the coalition might successfully employ traditional monopolistic "entry barriers".

Game-theoretic economic analysis provides some helpful insights into this question, but the open-access character of resource exploitation on the high seas complicates its applicability here. On the other hand, the game is asymmetric, with the incumbent coalition enjoying certain advantages.

Our analysis lends support to the thesis that usually leverage to enforce regional management control must be sought elsewhere, other than through direct application of economic power within the harvesting sector.
A PSEUDO "FOLK" THEOREM IN THE STRATEGIC PROVISION OF STOCK EXTERNALITIES
Authors: YANG ZILI
Published: January 2004

The paper discusses the relationship between the efficient provision and the Nash equilibrium of stock externalities in a dynamic setting. The following proposition has been proved: under certain conditions, the maximal gains of an agent in the economy by deviating from the Pareto optimal provision of stock externalities is less ∊, an arbitrary small positive number, when the time discount rate of the agents are sufficiently close to 0. Namely, under the same conditions, a Pareto efficient path is an ∊-Nash equilibrium where ∊ could be smaller than any predetermined level. The propositions are different from the folk theorems in repeated games because supporting of the ∊-Nash equilibrium does not require the threat of retaliations from other agents. The policy implications of the above results are also discussed here.
A NOTE ON NTU CONVEXITY AND POPULATION MONOTONIC ALLOCATION SCHEMES
Authors: HENDRICKX RUUD
Published: January 2004

For cooperative games with transferable utility, convexity has turned out to be an important and widely applicable concept, mainly because it implies some very nice and handy properties. One of these is that every extended marginal vector constitutes a population monotonic allocation scheme. In this note, this well-known result is generalised to games with nontransferable utility.
Cell-specific expression of SERCA, the exogenous Ca2+ transport ATPase, in cardiac myocytes
Authors: Ma Hailun , Sumbilla Carlota M. , Farrance Iain K. G. , Klein Michael G. , Inesi Giuseppe
Published: February 2004

We evaluated various constructs to obtain cell-specific expression of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) gene in cardiac myocytes after cDNA transfer by means of transfections or infections with adenovirus vectors. Expression of exogenous enhanced green fluorescent protein (EGFP) and SERCA genes was studied in cultured chicken embryo and neonatal rat cardiac myocytes, skeletal and smooth muscle cells, fibroblasts, and hepatocytes. Whereas the cytomegalovirus (CMV) promoter yielded high levels of protein expression in all cells studied, cardiac troponin T (cTnT) promoter segments demonstrated high specificity for cardiac myocytes. Their efficiency for protein expression was lower than that of the CMV promoter, but higher than that of cardiac myosin light chain or β-myosin heavy chain promoter segments. A double virus system for Cre-dependent expression under control of the CMV promoter and Cre expression under control of a cardiac-specific promoter yielded high protein levels in cardiac myocytes, but only partial cell specificity due to significant Cre expression in hepatocytes. Specific intracellular targeting of gene products was demonstrated in situ by specific immunostaining of exogenous SERCA1 and endogenous SERCA2 and comparative fluorescence microscopy. The -374 cTnT promoter segment was the most advantageous of the promoters studied, producing cell-specific SERCA expression and a definite increase over endogenous Ca2+-ATPase activity as well as faster removal of cytosolic calcium after membrane excitation. We conclude that analysis of promoter efficiency and cell specificity is of definite advantage when cell-specific expression of exogenous SERCA is wanted in cardiac myocytes after cDNA delivery to mixed cell populations.