bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel terpenoids from the Sea Hare Aplysia punctata
Authors: Findlay John A , Li Guoqiang
Published: January 2003

The structures of 23 compounds isolated from the sea hare Aplysia punctata have been determined by spectroscopic means. These include four new diterpenes (14): 1, neopargueroldione, is a tricyclic diterpene featuring a novel octane-1,5-dione A ring; 2 is deacetylparguerol; 3, punctatene acetate, shares the same [2:2:1] bicyclic system as dactylomelol from A. dactylomela; and 4, punctatol, has the same skeleton as laurencianol of algal origin. Diastereomeric sesquiterpenes 5 and 6 are similar to some compounds of algal origin, as is 7, perforatol, which shares the same carbon framework as perforatone from Laurentia perforata. In addition we have isolated 16 known compounds comprising 12 sesquiterpenes: perforenone, laurene, α-bromocuparane, α-isobromocuparane, laurinterol, debromoallolaurinterol, laurenisol, isofiliformin, obtusenol, β-snyderol, a dibromochamigrane, a friedosnyderane, two diterpenes: isoconncindiol and parguerol, and two C-15 acetogenins: laurenyne and laurencenyne. These known compounds have been reported previously either from other Aplysia species or from Laurencia species.Key words: Aplysia punctata, terpenoids, Sea Hare constituents.
Partial cuts in a trembling aspen  conifer stand: effects on microenvironmental conditions and regeneration dynamics
Authors: Prévost Marcel , Pothier David
Published: January 2003

We present the 5-year combined effects of different cutting intensities (removal of 0, 35, 50, 65, and 100% of basal area) and scarification on available light, soil temperature, and regeneration dynamics in a mixed aspen conifer stand in Quebec, Canada. Compared with the control, the 35% cut did not change transmitted light to the under story (<20% of full light), while the 50, 65, and 100% cuttings transmitted 30, 48, and 90% of full light, respectively, during the first summer. Trembling aspen (Populus tremuloides Michx.) suckering increased with percent basal area removal (p < 0.001). After 5 years, the 35 and 50% cuttings limited growth and survival of suckers (<1000 stems/ha, of which 5% are >1 m high), but the 65 and 100% cuttings favoured their development (8000 and 11 000 stems/ha, respectively, of which 29 and 38%, respectively, are >2 m high). Balsam fir (Abies balsamea (L.) Mill.) responded well to canopy opening alone with a maximal recruitment (31 000 seedlings/ha) in the 50% cut. Spruces (white spruce, Picea glauca (Moench) Voss, and red spruce, Picea rubens Sarg.) establish following scarification only, with a better response in the 65% cut (32 000 seedlings/ha) than in the 50 (15 000), 35 (10 000), and 0% (8000) cuttings.
Effects of contrasting light and soil moisture availability on the growth and biomass allocation of Douglas-fir and red alder
Authors: Chan Samuel S , Radosevich Steven R , Grotta Amy T
Published: January 2003

We examined growth and biomass allocation of individual Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) seedlings grown for 3 years under contrasting combinations of light and water. Alder growth was always greater than Douglas-fir. Full sunlight and soil moisture at field capacity caused large differences in size between the two species. With limited light and water, differences were smaller. Under full light and limited water, Douglas-fir allocated a high portion of its biomass to roots, whereas red alder allocated a high percentage to aboveground biomass components. Under light and water resource-limiting situations, red alder allocated more mass to stem, whereas Douglas-fir allocated more to roots. Red alder growth responded negatively to water limitation, whereas Douglas-fir did not. Red alder exhibited greater foliage plasticity to light. Species differences in size and allocation in response to resource availability may determine pathways by which Douglas-fir and red alder interact in a mixed community. Our findings support the hypothesis that the potential of species to use growth-limiting resources is an indicator of competitive ability. We suggest that red alder and Douglas-fir can co-exist under conditions of full light and limiting soil moisture availability. Furthermore, when contrasted with red alder, Douglas-fir's relatively greater tolerances to low light allow it to better persist in the understory. Red alder's rapid early growth and competitive ability will be superior under full light and nonlimiting soil moisture conditions.
Decomposition and element release from confined jack pine needle litter on and in the feathermoss layer
Authors: Morrison Ian K
Published: January 2003

An experiment was conducted in a mature boreal jack pine (Pinus banksiana Lamb.) stand comparing decomposition and element release rates of jack pine needle litter in mesh bags placed on the surface versus inserted into the feathermoss layer. There was a small but significant increase in decomposition rate of litter inserted into the feathermoss layer compared with litter placed on the surface, which persisted until at least the end of the fourth growing season of exposure. There were significantly lower N and P masses (reflecting more the loss of organic matter than change in element concentration) associated with inserted litter residues compared with residues of surface-placed litters. This result suggests a more rapid release of these elements. As feathermoss layers occupy the ground surface of many upland boreal conifer sites and most needle fall is quickly enveloped by this layer, insertion of litterbags into the feathermoss layer is a realistic representation of litterfall dynamics with implications for element cycling.
Community and population dynamics of sprucefir forests on Whiteface Mountain, New York: recent trends, 19852000
Authors: Battles John J , Fahey Timothy J , Siccama Thomas G , Johnson Arthur H
Published: January 2003

We remeasured two sets of permanent plots in old-growth, sprucefir forests on Whiteface Mountain to quantify ongoing vegetation dynamics at sites impacted by spruce decline. One set of plots was a stratified random sample of the vegetation in a subalpine watershed (Baldwin site). The other was selected to represent forest conditions in a high-elevation subset of the sprucefir forest (Esther site). Between 1987 and 1997, there was a significant increase in aboveground tree biomass at Baldwin with the majority of the increment due to the growth of canopy-sized trees. This growth occurred with little change in either species composition or size structure. The annual mortality rate of 1.2%·year1 for canopy-sized red spruce (Picea rubens Sarg.) in Baldwin almost matched the recruitment rate of 1.4 stems/ha per year. In addition, the relative growth rate of spruce was significantly faster than associated species. In contrast, spruce trees in Esther died at a rate of the 3.6%·year1 (19851995), and survivors grew more slowly than other species. The most obvious community-level trend at Esther (19852000) was an increase in overall tree density with most of this increase due to ingrowth of small trees. The demography of the spruce population at Baldwin suggests that the decline is over for at least this population.
Edge effects on epiphytic lichens in managed black spruce forests of eastern North America
Authors: Rheault Héloïse , Drapeau Pierre , Bergeron Yves , Esseen Per-Anders
Published: January 2003

We studied the spatial and temporal response of three epiphytic lichens (Bryoria spp., Evernia mesomorpha Nyl., and Usnea spp.) to edge effects in conifer forests of northwestern Quebec. Lichen abundance and substrate variables were sampled at four distances (5, 25, 50, and 100 m) from the edge in 15 edgeinterior transects in managed black spruce (Picea mariana (Mill.) BSP) forests. Responses to edge effects were assessed for short-term (13 years) and long-term (8 and 1623 years) periods. We also assessed the effect of forest fragment size on lichen abundance in 27 forest fragments ranging in size from 0.03 ha to >4 ha. We found a significant effect of distance to edge on mass of E. mesomorpha and Usnea spp. Lichen mass was lower in the first 50 m of edge compared with the forest interior (100 m). Size of forest fragments had no significant effect in any of the three lichens. However, mass of Usnea spp. was low in the seven smallest (<0.5 ha) fragments. Our results suggest that the response of epiphytic lichens to edge conditions could be used by forest managers as an indicator in determining the size of remnant stands that should be left to increase the proportion of interior forest habitat in harvested forest landscapes.
Pre-dispersal seed predation of white spruce cones in logged boreal mixedwood forest
Authors: Peters Susan , Boutin Stan , Macdonald Ellen
Published: January 2003

Predation of white spruce (Picea glauca (Moench) Voss) cones by red squirrels (Tamiasciurus hudsonicus Erxleben) was quantified in the mixedwood boreal forest of Alberta in cutblocks with seed tree retention and in adjacent uncut forest, during 3 years with varying levels of cone crop (1998, 1999, 2000). Percent cone loss was quantified by comparison of paired pre- and post-caching photographs of tree crowns. Cone loss from seed trees in cutblocks was significantly lower than from control trees in adjacent uncut forest (48.5 vs. 54.9%). Although the number of cones produced per tree declined by 42% and the percentage of trees producing cones declined by approximately 48% between 1998 and 2000, there was no corresponding increase in the percentage of cones harvested by squirrels. Percent cone loss was significantly lower from single seed trees in cutblocks, as compared with seed trees left in patches of more than 20 trees (33.4 vs. 50.5%). Cone predation significantly reduced the amount of seed available for natural regeneration using a seed tree system. Although blowdown may be reduced if seed trees are left in patches, leaving white spruce seed trees as singles in cutblocks may reduce the level of cone predation.
Refining tree recruitment models
Authors: Calogeropoulos C , Greene D F , Messier C , Brais S
Published: January 2003

We used a micrometeorological dispersal model to simulate seed and seedling distributions derived from subcanopy balsam fir (Abies balsamea (L.) Mill.) source trees in a trembling aspen (Populus tremuloides Michx.) dominated forest. Our first objective was to determine the effect of substituting basal area for cone production as a proxy for seed output. The results showed that the r2 from the regression of predicted versus observed densities increased by ~5% for seeds and ~15% for seedling simulations. Our second objective was to determine the effects of changing the median horizontal wind speed. The median speed in this forest environment varies according to the proportion of leaves abscised. For values of the median expected wind speed between the extremes of leafless and full-canopy forests, the r2 of predicted versus observed varied between 0.35 and 0.49 for seeds and between 0.33 and 0.62 for seedling simulations. We demonstrated that the simple one-dimensional model can have added precision if the dispersal parameters are chosen so as to allow more fine-scale variation.
Germination of pretreated Scots pine seeds after long-term storage
Authors: Hilli Anu , Tillman-Sutela Eila , Kauppi Anneli
Published: January 2003

Improvement of seed quality by pretreatments is indispensable in current mechanized plant production. Pretreated seeds are usually sown immediately, but in some cases they also have to be stored. The aim of our work was to study the changes in germination indices of pretreated Scots pine (Pinus sylvestris L.) seeds and the impact of the incubation temperature on germination after long-term storage. Pretreated and nontreated Scots pine seeds of three forest stands and a seed orchard were stored for about 10 years at the temperatures of 2°C and 18°C. The changes in germination indices were studied using germination tests and radiography. The germination indices of both pretreated and nontreated seeds were impaired during long-term storage. In general the changes were greater in cold than in frozen storage. Decline of the germination indices was more obvious in pretreated seed orchard than in forest stand seeds. The germination indices of forest stand seeds, whether pretreated or not, was preserved equally well in cold storage, while in orchard seeds germination indices prevailed better in nontreated seed batches. Forest stand seeds incubated at 10°C maintained their germination indices better than seeds incubated at 5°C, while in orchard seeds the effect was not as obvious.
Effectiveness of combinations of shelterwood, scarification, and feeding barriers to reduce pine weevil damage
Authors: Petersson Magnus , Örlander Göran
Published: January 2003

In a field experiment in southern Sweden we investigated the single and combined effects of shelterwood, soil scarification, and feeding barriers on pine weevil (Hylobius abietis L.) damage to Norway spruce (Picea abies (L.) Karst.) seedlings. The seedlings were planted on four different sites, each consisting of two plots, one clearcut and one with shelterwood (98148 stems/ha). These plots were each subdivided into two parts, one scarified and one left untreated. The seedlings were protected with insecticide or feeding barriers or left as unprotected controls. Three years after planting the mortality due to pine weevil damage was high (88%) for unprotected seedlings on clearcuts with no scarification. The damage-reducing effects of shelterwood, scarification, and physical protection were additive. Using all three methods in combination the mortality due to pine weevil feeding was less than 7% after 3 years. The order of effectiveness of the individual measures for reducing damage by pine weevils was insecticide, scarification, physical protection, and shelterwood. Scarification reduced pine weevil damage equally well on clearcuts as in shelterwoods. However, the effects of scarification were more long lasting in shelterwoods.
Promotion of flowering inEucalyptus nitensby paclobutrazol was enhanced by nitrogen fertilizer
Authors: Williams Dean R , Potts Brad M , Smethurst Philip J
Published: January 2003

We examined the effects of nitrogen and phosphorus fertilizer and paclobutrazol on flowering precocity and abundance in Eucalyptus nitens Deane & Maid. Trials to test these effects consisted of a factorial nitrogen by phosphorus experiment replicated on two sites and factorial nitrogen by paclobutrazol experiments conducted separately on reproductively immature and reproductively mature trees. The increase in tree size due to nitrogen fertilization increased the occurrence and abundance of precocious flower buds. However, the increase in tree size alone could not account for the nitrogen effect on flowering, indicating a secondary mechanism of flower induction by nitrogen. The application of both nitrogen fertilizer and paclobutrazol substantially increased the occurrence of precociously flowering trees over that of either treatment applied alone. The efficacy of both paclobutrazol and nitrogen in stimulating the flowering of the reproductively mature trees was affected by soil type, but this effect was overcome through the combination of nitrogen and paclobutrazol. The combination of nitrogen and paclobutrazol also restricted tree growth and combined applications on nitrogen deficient sites will be beneficial in commercial systems for producing eucalypt seed.
Foliage height influences specific leaf area of three conifer species
Authors: Marshall John D , Monserud Robert A
Published: January 2003

Specific leaf area (SLA), the ratio of projected leaf area to leaf dry mass, is a critical parameter in many forest process models. SLA describes the efficiency with which the leaf captures light relative to the biomass invested in the leaf. It increases from top to bottom of a canopy, but it is unclear why. We sampled stands with low and elevated canopies (young and old stands) to determine whether SLA is related to water potential, as inferred from branch height and length, or shade, as inferred from branch position relative to the rest of the canopy, or both. We studied western white pine (Pinus monticola Dougl. ex D. Don), ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.), and interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca) in northern Idaho. SLA decreased with branch height (P < 0.0001) at rates that varied among species (P < 0.0001). Branch length had no influence on SLA (P = 0.85). We detected no differences with canopy elevation (P = 0.90), but the slopes of lines relating SLA to branch height may have differed between the canopy elevation classes (P = 0.039). The results are consistent with predictions based on the hypothesis that SLA decreases as the gravitational component of water potential falls. The lack of a strong shading effect simplifies the estimation of canopy SLA for process models, requiring only species and branch heights.
Evaluation of sampling alternatives to quantify tree leaf area
Authors: Temesgen H
Published: January 2003

High within- and among-tree crown variation have contributed to the difficulty of tree-crown sampling and single-tree leaf area (area available for photosynthesis) estimation. Using reconstructed trees, simulations were used to compare five sampling designs for bias, mean square error (MSE), and distribution of the estimates. All sampling designs showed nearly zero bias. For most sample trees, stratified random sampling resulted in the lowest MSE values, followed by ellipsoidal, two-stage systematic, simple random, and then by two-stage unequal probability sampling. The poor performance of two-stage unequal probability sampling can be ascribed to the unequal probability of inclusion of first-order branches and twigs.
Development of Douglas-fir seedling root architecture in response to localized nutrient supply
Authors: Jacobs Douglass F , Rose Robin , Haase Diane L
Published: January 2003

Three months following sowing, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were transplanted into pots with controlled-release fertilizer (CRF) applied at rates of 0, 8, 16, and 24 g/2200 cm3 soil as a single uniform layer beneath the root system. Seedlings were destructively harvested periodically, and roots were divided into vertical segments above (S1), within (S2), and below (S3) the fertilizer layer. Two months following transplant, the number of active root tips was positively correlated with CRF rate in S1 and negatively correlated with rate in S2 and S3. At 6 months, root penetration into S3 was severely restricted at 16 and 24 g. This was attributed to detrimental changes in soil osmotic potential in S2. Fertilizer improved seedling growth at 8 g after 6 months compared with controls but was inhibitory at 24 g. Photochemical quantum yield was higher in all CRF treatments compared with controls 3 months following transplant, which corresponded with rapid initial CRF nutrient release. Despite improvements in nutrient release technology with CRF, high application rates may result in excessive concentrations of fertilizer nutrients in media, which can restrict root penetration and negatively affect seedling growth. Conservative application rates and improvements in CRF technology will help reduce the potential for adverse effects on seedling development.
Estimating impacts of resource management policies in the Foothills Model Forest
Authors: Patriquin Mike N , Alavalapati Janaki RR , Wellstead Adam M , Young Suzanne M , Adamowicz Wiktor L , White William A
Published: January 2003

This study examines the economic impact of policy changes in a forested region of the province of Alberta known as the Foothills Model Forest (FMF). The effects of policy changes in various sectors are analyzed in terms of all sectors of the regional economy with particular emphasis on the forestry sector. Unlike most analyses of regional policies, this study uses a computable general equilibrium (CGE) framework rather than a fixed-price framework to analyze economy-wide impacts of land use or forest policy changes. The application of this technique on a regional scale is rare in the scientific literature. Model results indicate that a decrease in forestry output somewhat offsets the positive economic impact generated by increased visitor activity. Failure to consider these trade-off impacts in the analysis will result in erroneous conclusions. The outcomes from three timely policy scenarios are examined in this paper. The results from the CGE framework suggest that policy makers face a greater degree of complexity than in current economic impact frameworks.
Belowground biomass dynamics in the Carbon Budget Model of the Canadian Forest Sector: recent improvements and implications for the estimation of NPP and NEP
Authors: Li Zhong , Kurz Werner A , Apps Michael J , Beukema Sarah J
Published: January 2003

In the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2), root biomass and dynamics are estimated using regression equations based on the literature. A recent analysis showed that some of these equations might overestimate belowground net primary production (NPPB). The objectives of this study were to update the compilation of root biomass and turnover data, to recalculate the regression equations and to evaluate the impact of the new equations on CBM-CFS2 estimates of net primary production (NPP) and net ecosystem production (NEP). We updated all equations based on 635 pairs of aboveground and belowground data compiled from published studies in the cold temperate and boreal forests. The new parameter for the equation to predict total root biomass for softwood species changed only slightly, but the changes for hardwood species were statistically significant. A new equation form, which improved the accuracy and biological interpretation, was used to predict fine root biomass as a proportion of total root biomass. The annual rate of fine root turnover was currently estimated to be 0.641 of fine root biomass. A comparison of NPP estimates from CBM-CFS2 with results from field measurements, empirical calculations and modeling indicated that the new root equations predicted reasonable NPPBvalues. The changes to the root equations had little effect on NEP estimates.
The use of multiple measurement techniques to refine estimates of conifer needle geometry
Authors: Bond-Lamberty B , Wang C , Gower S T
Published: January 2003

Knowledge of foliar surface area is important in many fields, but estimating the area of nonflat conifer needles is difficult. The primary goal of this study was to use optical scanning and immersion methods to test and refine the standard cross-sectional geometries assumed for black spruce (Picea mariana (Mill.) BSP) and jack pine (Pinus banksiana Lamb.) needles. Projected leaf area (PLA, measured using a flatbed scanner), and hemisurface leaf area (HSLA, estimated from water immersion) were compared for conifer samples from a 37-year-old even-aged stand in northern Manitoba, Canada. The HSLAPLA relationship was used to infer information about needle cross-sectional geometry after assuming a basic form (rhombus for black spruce and hemiellipse for jack pine). The cross section of black spruce needles was best approximated as a rhombus with a major/minor diagonal ratio of 1.35. Jack pine needles were best described by a hemiellipse with major/minor axis ratio of 1.30. Minor but incorrect assumptions of needle cross-sectional geometry resulted in foliar area errors of 68% using scanning methods and 12% using immersion methods. Simple equations are presented to calculate hemisurface needle area from volume or projected needle area based on these refined parameters.
Effects of a wide gradient of retained tree structure on understory light in coastal Douglas-fir forests
Authors: Drever C Ronnie , Lertzman Kenneth P
Published: January 2003

We characterize understory light of seven stands that varied along a gradient of tree retention. Using hemispherical canopy photographs and digital image, we estimated gap light or solar radiation reaching the understory through the canopy. Using nonlinear regressions, we related gap light to several structural attributes in the examined silvicultural treatments. The silvicultural treatments affected both the median and range of gap light in the understory. As overstory removal increased from uncut second growth to green-tree retention, the median value of light increased from 8 to 68% full sun, while the range of light increased from 322% to 2688% full sun. We found strong, significant, and negative nonlinear relationships between gap light at a particular microsite (0.04 ha) in the understory and the height, diameter at breast height, density, and volume of surrounding retained trees (ra2 = 0.770.94). These relationships can aid planning of treatments that retain forest structure, such as variable retention, by allowing predictions of understory light from commonly used field data. These predictions allow forest managers to understand some of the ecological consequences and tradeoffs associated with retaining structure during harvesting.
Stand density index in uneven-aged ponderosa pine stands
Authors: Woodall C W , Fiedler C E , Milner K S
Published: January 2003

Stand density index (SDI) was developed to quantify relative stand density in even-aged stands. Application of SDI in uneven-aged stands has been described mathematically but not justified biologically. Diameter-class trends in SDI and sapwood area across 14 uneven-aged ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) stands in eastern Montana were examined to elucidate the biological underpinnings of the SDI summation method. Results indicate that the SDI summation method is biased in its apportionment of relative stand density across diameter classes in uneven-aged ponderosa pine stands. SDI apportions greater relative density to small trees than to larger ones. Therefore, SDI may overpredict site occupancy for reverse J-shaped diameter distributions with more small trees than large ones, and it may underpredict occupancy with nonreverse J-shaped diameter distributions. Application of the SDI summation method in uneven-aged ponderosa pine stands may be biologically justified only if site occupancy  diameter-class trends are taken into account when interpreting SDI values. Replacing the self-thinning scaling factor of the SDI summation method with more biologically relevant scaling relationships may create improved relative density measures for uneven-aged stands.
Nitrogen uptake characteristics for roots of conifer seedlings and common boreal forest competitor species
Authors: Hangs Ryan D , Knight J Diane , Van Rees Ken CJ
Published: January 2003

Little is known about the N uptake abilities of competitor species and planted seedlings in the boreal forest. The objective of this study was to determine the MichaelisMenten kinetic parameters of NH4+and NO3for white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings, and three competitive common boreal forest early successional species: aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and cala magrostis (Calamagrostis canadensis (Michx.) Beauv.). Uptake kinetics were measured in hydroponic cultures and expressed as maximum uptake (Imax) and ion affinity (Km). The ranking of Imaxvalues (pmol·cm-2·s1) for NH4+uptake was calamagrostis (84.6), fireweed (58.1), white spruce (20.7), aspen (12.5), and jack pine (10.9), and for NO3uptake was calamagrostis (17.7), fireweed (12.5), aspen (5.8), white spruce (4.5), and jack pine (2.1). The ranking of Kmvalues (µM) for NH4+uptake was calamagrostis (125.9), fireweed (163.8), aspen (205.7), white spruce (217.1), and jack pine (270.5), and for NO3uptake was calamagrostis (229.9), fireweed (274.6), aspen (336.5), white spruce (344.5), and jack pine (350.5). Calamagrostis exhibited the greatest uptake rates and affinity for NH4+and NO3, suggesting that silviculture practices that specifically reduce establishment of this grass should benefit the growth of planted seedlings.
CASIMIR SCALING AND MODELS OF CONFINEMENT IN QCD
Authors: SHEVCHENKO V. I. , SIMONOV YU. A.
Published: January 2003

Recent lattice calculations have demonstrated that the QCD static potential for sources in different representations of the gauge group is proportional to the eigenvalue of the corresponding quadratic Casimir operator with an accuracy of a few percent. We discuss the present theoretical status of this "Casimir scaling" phenomenon and stress its importance for the analysis of nonperturbative QCD vacuum models and other field theories. It is argued that Casimir scaling strongly advocates the property of Gaussian dominance of nonperturbative QCD vacuum. We also briefly discuss possible future tests to improve our understanding of the phenomenon.
THE GENERAL COSET ORBIFOLD ACTION
Authors: HALPERN M. B. , WAGNER F.
Published: January 2003

Recently an action formulation, called the general WZW orbifold action, was given for each sector of every WZW orbifold. In this paper we gauge this action by general twisted gauge groups to find the action formulation of each sector of every coset orbifold. Connection with the known current-algebraic formulation of coset orbifolds is discussed as needed, and some large examples are worked out in further detail.
GENOMIC ORGANIZATION AND HOPFIELD'S MODEL OF ASSOCIATIVE MEMORY
Authors: TORRES JOSÉ-LEONEL , TRAINOR LYNN
Published: January 2003

We consider a description of genomic organization based on a neural network model of associative memory (Hopfield's model). This description is consonant with the view that the cell cycle involves transitions between successive phases, each entailing an assortment of metabolically distinct states. A picture emerges where a cell at a particular state in its life cycle fulfills its metabolic needs through a specific set of genetic patterns, comprising a characteristic, stable one, plus those belonging to its basin of attraction in the sense of the neural network metaphor. A gene may belong to more than one stable configuration, so its function will depend on its context as defined by the particular pattern playing a dominant role at any given moment. The model provides a conceptual framework in genomic analysis and yields quantitative results in some cases, that can be assessed using observable data. For example, it allows consideration of a genome's resilience under variation of its genetic interactions. It also suggests an upper bound on the number of stable genetic patterns in prokaryotes and archaeons, close to 14% of their total endowment of genes. We test this estimate against available information from sequenced genomes.
CLUSTERING PANEL DATA VIA PERTURBED ADAPTIVE SIMULATED ANNEALING AND GENETIC ALGORITHMS
Authors: BONZO DANIEL C. , HERMOSILLA AUGUSTO Y.
Published: January 2003

Non-hierarchical cluster analysis for panel data is known to be hampered by structural preservation, computational complexity and efficiency, and dependency problems. Resolving these issues becomes increasingly important as efficient collection and maintenance of panel data make application more conducive.

To address some computational issues and structural preservation, Bonzo [3] presented a stochastic version of Kosmelj and Batagelj's approach [16] to clustering panel data. The method used a probability link function (instead of the usual distance functions) in defining cluster inertias with the aim of preserving the clusters' probabilistic structure. Formulating clustering as an optimization problem, the objective function allows the application of heuristic and stochastic optimization techniques.

In this paper, we present a modified heuristic for adaptive simulated annealing (ASA) by perturbing the state vector's sampling distribution, specifically, by perturbing the drift of a diffusion process. Such an approach has been used to hasten convergence towards global optimum at equilibrium for diversely complex, combinatorial, and large-scale systems. The perturbed ASA (PASA) heuristic is then embedded in a genetic algorithm (GA) procedure to hasten and improve the stochastic local search process. The PASA-GA hybrid can be further modified and improved such as by explicit parallel implementation.
GENETIC REPRESENTATION AND GENETIC NEUTRALITY IN GENE EXPRESSION PROGRAMMING
Authors: FERREIRA CÂNDIDA
Published: January 2003

The neutral theory of molecular evolution states that the accumulation of neutral mutations in the genome is fundamental for evolution to occur. The genetic representation of gene expression programming, an artificial genotype/phenotype system, not only allows the existence of non-coding regions in the genome where neutral mutations can accumulate but also allows the controlled manipulation of both the number and the extent of these non-coding regions. Therefore, gene expression programming is an ideal artificial system where the neutral theory of evolution can be tested in order to gain some insights into the workings of artificial evolutionary systems. The results presented in this work show beyond any doubt that the existence of neutral regions in the genome is fundamental for evolution to occur efficiently.
SUM RULE FOR MULTISCALE REPRESENTATIONS OF KINEMATICALLY DESCRIBED SYSTEMS
Authors: BAR-YAM YANEER
Published: January 2003

We derive a sum rule that constrains the scale based decomposition of the trajectories of finite systems of particles. The sum rule reflects a tradeoff between the finer and larger scale collective degrees of freedom. For short duration trajectories, where acceleration is irrelevant, the sum rule can be related to the moment of inertia and the kinetic energy (times a characteristic time squared). Thus, two nonequilibrium systems that have the same kinetic energy and moment of inertia can, when compared to each other, have different scales of behavior, but if one of them has larger scales of behavior than the other, it must compensate by also having smaller scales of behavior. In the context of coherence or correlation, the larger scale of behavior corresponds to the collective motion, while the smaller scales of behavior correspond to the relative motion of correlated particles. For longer duration trajectories, the sum rule includes the full effective moment of inertia of the system in space-time with respect to an external frame of reference, providing the possibility of relating the class of systems that can exist in the same space-time domain.
DIFFUSION OF A POPULATION OF INTERACTING REPLICATORS IN SEQUENCE SPACE
Authors: STADLER BÄRBEL M. R.
Published: January 2003

We consider a simple model for catalyzed replication. Computer simulations show that a finite population moves in sequence space by diffusion analogous to the behavior of a quasispecies on a flat fitness landscape. The diffusion constant depends linearly on the per position mutation rate and the ratio of sequence length and population size.
Evaluating the competitive effects of mergers of internet backbone providers
Authors: Besen Stanley M. , Spigel Jeffrey S. , Srinagesh Padmanabhan
Published: January 2003

This article analyzes the usefulness of the traffic measurement methodologies used by the European Commission (EC) and the United States Department of Justice (DOJ) in assessing the competitive effects of mergers of Internet backbone providers. The analysis concludes that the traffic ratios used by the EC to estimate market shares when it reviewed the merger application of MCI and WorldCom, and by the EC and the DOJ when they reviewed the proposed merger of Sprint and MCI WorldCom, have significant limitations. In particular, the article shows that these measurements provide a potentially misleading picture of the effect of a merger of backbone providers, even under the assumption that the Internet is a rigid hierarchy, and that this problem is likely to become worse as the use of secondary peering, multihoming, and intelligent content distribution services become more widespread.
Self-similarity in the web
Authors: Dill Stephen , Kumar Ravi , Mccurley Kevin S. , Rajagopalan Sridhar , Sivakumar D. , Tomkins Andrew
Published: January 2003

Algorithmic tools for searching and mining the Web are becoming increasingly sophisticated and vital. In this context, algorithms that use and exploit structural information about the Web perform better than generic methods in both efficiency and reliability.We present an extensive characterization of the graph structure of the Web, with a view to enabling high-performance applications that make use of this structure. In particular, we show that the Web emerges as the outcome of a number of essentially independent stochastic processes that evolve at various scales. A striking consequence of this scale invariance is that the structure of the Web is "fractal"---cohesive subregions display the same characteristics as the Web at large. An understanding of this underlying fractal nature is therefore applicable to designing data services across multiple domains and scales.We describe potential applications of this line of research to optimized algorithm design for Web-scale data analysis.
Engineering web cache consistency
Authors: Yin Jian , Alvisi Lorenzo , Dahlin Mike , Iyengar Arun
Published: January 2003

Server-driven consistency protocols can reduce read latency and improve data freshness for a given network and server overhead, compared to the traditional consistency protocols that rely on client polling. Server-driven consistency protocols appear particularly attractive for large-scale dynamic Web workloads because dynamically generated data can change rapidly and unpredictably. However, there have been few reports on engineering server-driven consistency for such workloads. This article reports our experience in engineering server-driven consistency for a sporting and event Web site hosted by IBM, one of the most popular sites on the Internet for the duration of the event. We also examine an e-commerce site for a national retail store. Our study focuses on scalability and cachability of dynamic content. To assess scalability, we measure both the amount of state that a server needs to maintain to ensure consistency and the bursts of load in sending out invalidation messages when a popular object is modified. We find that server-driven protocols can cap the size of the server's state to a given amount without significant performance costs, and can smooth the bursts of load with minimal impact on the consistency guarantees. To improve performance, we systematically investigate several design issues for which prior research has suggested widely different solutions, including whether servers should send invalidations to idle clients. Finally, we quantify the performance impact of caching dynamic data with server-driven consistency protocols and the benefits of server-driven consistency protocols for large-scale dynamic Web services. We find that (i) caching dynamically generated data can increase cache hit rates by up to 10%, compared to the systems that do not cache dynamically generated data; and (ii) server-driven consistency protocols can increase cache hit rates by a factor of 1.5-3 for large-scale dynamic Web services, compared to client polling protocols. We have implemented a prototype of a server-driven consistency protocol based on our findings by augmenting the popular Squid cache.
User authentication through keystroke dynamics
Authors: Bergadano Francesco , Gunetti Daniele , Picardi Claudia
Published: January 2003

Unlike other access control systems based on biometric features, keystroke analysis has not led to techniques providing an acceptable level of accuracy. The reason is probably the intrinsic variability of typing dynamics, versus other---very stable---biometric characteristics, such as face or fingerprint patterns. In this paper we present an original measure for keystroke dynamics that limits the instability of this biometric feature. We have tested our approach on 154 individuals, achieving a False Alarm Rate of about 4% and an Impostor Pass Rate of less than 0.01%. This performance is reached using the same sampling text for all the individuals, allowing typing errors, without any specific tailoring of the authentication system with respect to the available set of typing samples and users, and collecting the samples over a 28.8-Kbaud remote modem connection.
Improving the granularity of access control for Windows 2000
Authors: Swift Michael M. , Hopkins Anne , Brundrett Peter , Van Dyke Cliff , Garg Praerit , Chan Shannon , Goertzel Mario , Jensenworth Gregory
Published: January 2003

This article presents the mechanisms in Windows 2000 that enable fine-grained and centrally managed access control for both operating system components and applications. These features were added during the transition from Windows NT 4.0 to support the Active Directory, a new feature in Windows 2000, and to protect computers connected to the Internet. While the access control mechanisms in Windows NT are suitable for file systems and applications with simple requirements, they fall short of the needs of applications with complex data objects. Our goal was to use operating system access control mechanisms to protect a large object hierarchy with many types of objects, each with many data properties. We also wanted to reduce the exposure of users to untrustworthy or exploited programs.We introduced three extensions to support these goals. First, we extended the entries in access control lists to provide an unlimited number of access rights for a single object and to allow grouping those rights for efficiency. Second, we extended the entries to specify precisely how access control lists are assigned to each distinct type of object, instead of treating all types identically. Finally, we extended the data structure identifying users' identity to the operating system to allow users to restrict the set of objects a program may access. These changes allow a single access control mechanism to be used to protect both system and application resources, as well as protect users from each other and users from their programs, simplifying both program development and system management.
The economics of information security investment
Authors: Gordon Lawrence A. , Loeb Martin P.
Published: January 2003

This article presents an economic model that determines the optimal amount to invest to protect a given set of information. The model takes into account the vulnerability of the information to a security breach and the potential loss should such a breach occur. It is shown that for a given potential loss, a firm should not necessarily focus its investments on information sets with the highest vulnerability. Since extremely vulnerable information sets may be inordinately expensive to protect, a firm may be better off concentrating its efforts on information sets with midrange vulnerabilities. The analysis further suggests that to maximize the expected benefit from investment to protect information, a firm should spend only a small fraction of the expected loss due to a security breach.
A methodology for analyzing the performance of authentication protocols
Authors: Harbitter Alan , Menascé Daniel A.
Published: January 2003

Performance, in terms of user response time and the consumption of processing and communications resources, is an important factor to be considered when designing authentication protocols. The mix of public key and secret key encryption algorithms typically included in these protocols makes it difficult to model performance using conventional analytical methods. In this article, we develop a validated modeling methodology to be used for analyzing authentication protocol features, and we use two examples to illustrate the methodology. In the first example, we analyze the environmental parameters that favor one proposed public-key-enabled Kerberos variant over another in the context of a large, multiple-realm network. In the second example, we propose a Kerberos variant for a mobile computing environment and analyze the performance benefits realized by introducing a proxy to offload processing and communications workload.
A model of OASIS role-based access control and its support for active security
Authors: Bacon Jean , Moody Ken , Yao Walt
Published: January 2003

OASIS is a role-based access control architecture for achieving secure interoperation of services in an open, distributed environment. The aim of OASIS is to allow autonomous management domains to specify their own access control policies and to interoperate subject to service level agreements (SLAs). Services define roles and implement formally specified policy to control role activation and service use; users must present the required credentials, in an appropriate context, in order to activate a role or invoke a service. All privileges are derived from roles, which are activated for the duration of a session only. In addition, a role is deactivated immediately if any of the conditions of the membership rule associated with its activation becomes false. These conditions can test the context, thus ensuring active monitoring of security.To support the management of privileges, OASIS introduces
appointment
. Users in certain roles are authorized to issue other users with
appointment certificates
, which may be a prerequisite for activating one or more roles. The conditions for activating a role at a service may include appointment certificates as well as prerequisite roles and constraints on the context. An appointment certificate does not therefore convey privileges directly but can be used as a credential for role activation. The lifetime of appointment certificates is not restricted to the issuing session, so they can be used as long-lived credentials to represent academic and professional qualification, or membership of an organization.Role-based access control (RBAC), in associating privileges with roles, provides a means of expressing access control that is scalable to large numbers of principals. However, pure RBAC associates privileges only with roles, whereas applications often require more fine-grained access control. Parametrized roles extend the functionality to meet this need.We motivate our approach and formalise OASIS. We first present the overall architecture through a basic model, followed by an extended model that includes parametrization.
The world-wide telescope
Authors: Gray Jim , Szalay Alex
Published: January 2003

Mining vast databases of astronomical data, this new online way to see the global structure of the universe promises to be not only a wonderful virtual telescope but an archetype for the evolution of computational science.
SETI@home
Authors: Anderson David P. , Cobb Jeff , Korpela Eric , Lebofsky Matt , Werthimer Dan
Published: January 2003

Millions of computer owners worldwide contribute computer time to the search for extraterrestrial intelligence, performing the largest computation ever.
Volume-rendered galactic animations
Authors: Genetti Jon
Published: January 2003

How a 40-billion-pixel Orion Nebula visualization was rendered for a 9.1-million-pixel display at the Hayden Planetarium of the American Museum of Natural History.
Ten unmyths of project estimation
Authors: Armour Phillip
Published: January 2003

Reconsidering some commonly accepted project management practices.
Sorting out software complexity
Authors: Glass Robert L.
Published: January 2003

Underlying complexity escalates exponentially: some little-known research findings.
New surveillance techniques raise privacy concerns
Authors: Gelbord Boaz , Roelofsen Gert
Published: January 2003

How much privacy are citizens willing to surrender in the interest of public safety?
A complex systems perspective on computer-supported collaborative design technology
Authors: Klein Mark , Sayama Hiroki , Faratin Peyman , Bar-Yam Yaneer
Published: January 2003

What can be done to better support collaborative innovation?
On-the-fly web content integrity check boosts users' confidence
Authors: Sedaghat Soroush , Pieprzyk Josef , Vossough Ehsan
Published: January 2003

Malicious attacks on Web servers by intruders and hackers are prime concerns of organizations, administrators of Web sites, as well as users who access them.