bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of glacitectonic fractures on wall failure in open excavations: Heath Steele Mines, New Brunswick, Canada
Authors: Park Adrian F , Broster Bruce E
Published: May 2008

Recognition and detailed mapping of glacigenic fractures and reactivated joints, along with such glacigenic features as striae and till fabrics, prove critical in predicting ground control hazards such as pit wall failure. Following a period of heavy rain in the autumn of 1991, a failure occured on part of the wall of an open-pit mining operation on the Heath Steel Mines property. The failure surfaces bounding the complex landslips of the pit wall were all either original glacigenic fractures or other joints reactivated during Late Wisconsinan glacier overriding. Apart from differential movement, such features include joints filled with coarse sand or clay. Comparaison of the geometry of glacigenic fractures in failed areas with the same features in areas just as densely fractured, but which did not fail, reveal a combination of circumstances where failure was predictable. In this case failure of an unstable rock mass resulted from unfavourable kinematic relationships involving the following: the low strength of clay- and sand-filled joints, the presence of highly permeable and weathered joint conduits, the unfavourable geometry between wall and joint orientation, and an occurrence of increased fluid pressure along the joints from high rainfall that triggered movement.

Key words: glacitectonics, geotechnical, wall failure, excavations, rock-quality data, instability.
Analysis of case histories from construction of the Central Expressway in Singapore
Authors: Wong I H , Poh T Y , Chuah H L
Published: May 2008

The construction of the cut-and-cover tunnels and depressed roadways of the Central Expressway (CTE) Phase II, Singapore, involved deep excavations. An extensive instrumentation program was carried out to monitor the behaviour of the excavations. The performance of three instrumented excavations from the construction of the CTE Phase II have been documented and analyzed using the finite element method (EXCAV) or finite difference method (FLAC). The results of the analyses show that the computed wall movements agree well with field measurements of wall movement and the computed wall bending moments generally agree quite well with those obtained from back-calculation.

Key words: deep excavation, stiff clay, numerical analysis, displacements.
Liquid limits and fall cones
Authors: Leroueil Serge , Le Bihan Jean-Pierre
Published: May 2008

The Bureau de normalisation du Québec and the Canadian Standards Association developed standards for the determination of the liquid limit using the fall cone method and the percussion method. This technical note compares the liquid limit values obtained with these two methods and also compares them with those obtained using methods and standards developed in other countries.

Key words: clays, liquid limits, fall cone, standards.
Anchor rod forces and maximum bending moments in sheet pile walls using the factored strength approach
Authors: Schriver A B , Valsangkar A J
Published: May 2008

Recently, the limit states approach using factored strength has been recommended in geotechnical design. Some recent research has indicated that the application of limit states design using recommended load and strength factors leads to conservative designs compared with the conventional methods. In this study the influence of sheet pile wall geometry, type of water pressure distribution, and different methods of analysis on the maximum bending moment and achor rod force are presented. Recommendations are made to make the factored strength design compatible with conventional design.

Key words: factored strength, working stress design, ultimate limit state design, anchored sheet pile wall, bending moment, anchor rod force.
Effect of intermediate principal stress on the deformation response of sand
Authors: Sãyao A , Vaid Y P
Published: May 2008

An experimental investigation of the relevance of the intermediate principal stress (σ2) on the deformation response of a sand is presented. The effects of σ2 are conveniently studied through the nondimensional stress parameter b = (σ2  σ3)/(σ1  σ3). A series of stress path tests was performed on Ottawa sand specimens in a hollow cylinder torsional shear device. The experimental program includes shear loading at different values of b, and special b tests, in which b was continuously varied at different stress directions. It is shown that the b value may have a significant influence on the stressstrain response of sand, depending on the loading conditions.

Key words: hollow cylinder tests, generalized stress paths, sand, stressstrain behaviour, intermediate principal stress.
Void redistribution in sand under post-earthquake loading
Authors: Boulanger Ross W , Truman Stephen P
Published: May 2008

A mechanism for void redistribution in an infinite slope under post-earthquake loading conditions is described by consideration of the in situ loading paths that can occur under post-earthquake conditions and the results of triaxial tests designed to represent specific in situ post-earthquake loading paths. The mechanism is illustrated by application to an example problem. Void redistribution is shown to be a phenomena that may be more pronounced at the field scale than at the laboratory scale.

Key words: liquefaction, earthquake, void redistribution, triaxial, sand.
The role of particle breakage in pile creep in sand
Authors: Leung C F , Lee F H , Yet N S
Published: May 2008

It has been reported in the literature that the settlement of pile foundations in sand under sustained service loads is time dependent. As this phenomenon is not well understood, an experimental study is conducted to investigate the mechanism of pile creep in sand. In the first part of the study involving centrifuge modelling of piles, the test results show that the pile settlement increases with the logarithm of time and the rate of settlement increase is dependent upon the magnitude of applied load and sand density. The changes in the soil and pile stresses observed from instruments installed in the soil and along the pile shaft reveal that under sustained loads, stress relaxation takes place at and around the pile tip area with consequent stress transfer to the shaft. Associated ground surface settlement shows that creep is related to volumetric compression rather than dilation of sand. The centrifuge test findings are then related to the creep behaviour of sand subjected to one-dimensional compression. Examination of sand particles before and after sustained compression loads reveals that sand grains have been broken with their angular protrusions gradually ground off with time. The phenomena of sand particle breakage and stress relaxation around the pile tip provide evidence for the hypothesis that the observed creep is due to the progressive breakdown of sand particules.

Key words: centrifuge models, creep, mechanism, one-dimensional compression, pile, sand.
Modelling of light nonaqueous phase liquid (LNAPL) releases into unsaturated sand
Authors: Knight M A , Mitchell R J
Published: May 2008

Centrifuge physical modelling of light nonaquaeous phase liquid (LNAPL) transport in an unsaturated sand is discussed with regard to the similitude of the resulting three-fluid flow. Three model series are reported: the first to establish a reproducible unsaturated moisturesuction profile; the second to examine the modelling of models methodology for evaluating similitude of an LNAPL release into an unsaturated fine sand; and the third to prototype-scale data sets for 1000 L surface LNAPL releases at two different rates. Results show that a slower release rate produces deeper LNAPL penetration, and the reasons for this behaviour are discussed. An inexpensive and readily available numerical code called SWANFLOW was used to independently simulate the prototype release rates, and the results are compared with the centrifuge data. The numerical simulations produced compatible predictions of short-term oil transport but did not predict the observed longer term fate of the LNAPL in this highly nonlinear imbibitiondrainage problem. A numerical code that incorporates hysteresis between the imbibition and drainage curves would be expected to produce more complete long-term predictions.

Key words: centrifuge modelling, numerical simulation, LNAPL fate, unsaturated sand.
Eighteenth Canadian Geotechnical Colloquium: Limit States Design For Foundations. Part I. An overview of the foundation design process
Authors: Becker Dennis E
Published: May 2008

This paper examines the foundation design process in terms of level of safety associated with current state-of-practice, sources of uncertainty and how they are handled, importance of engineering judgement and experience, and the role of codes of practice. Working stress, limit states, reliability-based design approcahes are described and discussed in terms of their historical development, fundamental bases and differences, advantages, and limitations. Limit states are conditions under which a structure no longer performs its intended function. Limit states design considers seperately the two classes of ultimate and serviceability limit states using partial factors of safety. The European factored strength approach and the North American factored overall resistance approach are compared and discussed. The factored resistance approach is a logical extension of working stress design and has the significant advantage that it reflects not only uncertainty in strength, but also in theoretical models, site conditions, construction tolerances, and failure mechanisms. The partial load and resistance factors are interrelated and are a function of characteristic values. A consistent, rational basis for the selection of the geotechnical characteristic value is required. The use of a conservatively assessed mean value is recommended, and an approach for its interpretation is presented.

Key words: limit states design, working stress design, characteristic value, partial factors, factored resistance, load and resistance factor design.
The pre-European settlement forest composition of the Miramichi River watershed, New Brunswick, as reconstructed using witness trees from original land surveys
Authors: Aubé Mélanie
Published: May 2008

The goal of this investigation was to characterize the pre-European settlement forest composition of the Miramichi River watershed using witness trees to contribute to the definition of a baseline for assessing changes over time in the Acadian forest. The witness tree data were stratified by ecoregion and by ecosite, for the portions of the watershed that are in the Northern Uplands, Continental Lowlands, and Eastern Lowlands ecoregions of New Brunswick, as well as by riparian and inland forest; and pre-settlement forest composition (1787–1847) was compared with current forest composition (1998–2000). The witness tree data constitute evidence that a distinctive riparian forest existed before European settlement and that the difference between riparian and inland forest has lessened. They show that the proportions of Betula spp., Tsuga canadensis (L.) Carrière, Ulmus americana L., and Thuja occidentalis L. have decreased; that the proportion of Acer spp. has increased and that Picea spp. and Abies balsamea (L.) Mill. var. balsamea have maintained their overall dominance of the forest in number of individuals, and have increased it on at least 50% of the watershed area.
Modeling percent stocking changes for lodgepole pine stands in Alberta
Authors: Yang Yuqing , Huang Shongming
Published: May 2008

A percent stocking change model was developed for lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) in Alberta based on spatially mapped permanent sample plot data. Percent stocking was defined as the percentage of 10 m2 subplots occupied by at least one tree with a minimum height of 1.3 m. The difference equation technique was employed to fit the model. Three model forms were examined and the logistic function was chosen as the final model. Site index was found to be a significant predictor and incorporated into the model. Analyses revealed that the model had correlated, but homoskedastic errors and the correlated errors were modeled by spherical covariance structure using NLINMIX macro in SAS. A percent stocking index, defined as the percent stocking at 50 years total age, was introduced and derived from the developed model. The percent stocking model had both forward and backward projection capabilities. It was demonstrated, both on model fitting and validation data, that the model adequately portrayed the percent stocking dynamics of lodgepole pine stands in Alberta. The model also provided an important basis for creating linkages between reforestation survey results and future yield, which is crucial for sustainable forest management.
Mycorrhizal fungal community relationship to root nitrogen concentration over a regional atmospheric nitrogen deposition gradient in the northeastern USA
Authors: Lilleskov Erik A. , Wargo Philip M. , Vogt Kristiina A. , Vogt Daniel J.
Published: May 2008

Increased nitrogen (N) input has been found to alter ectomycorrhizal fungal communities over short deposition gradients and in fertilization experiments; however, its effects over larger spatial scales have not been determined. To address this gap, we reanalyzed data from a study originally designed to examine the effects of soil aluminum/calcium (Al/Ca) ratios on the vitality of red spruce fine roots over a regional acid and N deposition gradient in the northeastern USA. We used root N as an indicator of stand N availability and examined its relationship with the abundance of ectomycorrhizal morphotypes. The dominant morphotypes changed in relative abundance as a function of stand N availability. As root N concentrations increased, Piloderma spp. - like, Cenococcum geophilum Fr., and other unidentified mycorrhizal morphotypes declined in abundance, while other smooth-mantled morphotypes increased. Root N concentration in the 1–2 mm diameter class was the best predictor of the abundance of multiple morphotypes. The morphotype responses were consistent with those found in experimental and small-scale studies, suggesting that N availability is altering ectomycorrhizal communities over broad spatial scales in this region. This finding provides an impetus to conduct a more detailed characterization of mycorrhizal community responses to N deposition across large-scale gradients.
Nitrogen limitation in a sweetgum plantation: implications for carbon allocation and storage
Authors: Iversen Colleen M. , Norby Richard J.
Published: May 2008

The N status of temperate forests is closely linked to their C fluxes, and altered C or N availability may affect ecosystem C storage through changes in forest production and C allocation. We proposed that increased fine-root production previously observed in a sweetgum ( Liquidambar styraciflua L.) forest in response to elevated [CO2] was a physiological response to N limitation. To examine this premise, we fertilized plots in the sweetgum plantation adjacent to the Oak Ridge National Laboratory free-air CO2-enrichment (FACE) experiment. We hypothesized that N fertilization would increase sweetgum net primary production, leaf [N], and the relative flux of C to wood production. Annual additions of 200 kg·ha–1 of N as urea increased soil N availability, which increased stand net primary production, stand N uptake, and N requirement by about one-third. Increased leaf [N] and leaf area production in the fertilized plots increased stem production and shifted relative flux of C to wood production. We conclude that sweetgum production on this site is limited by soil N availability and a decreased fraction of net primary production in fine-root production with N addition is consistent with the premise that increased fine-root production in the adjacent FACE experiment is in response to N limitation.
Genetic structures of common ash (Fraxinus excelsior) populations in Germany at sites differing in water regimes
Authors: Dacasa Rüdinger M. C. , Glaeser J. , Hebel I. , Dounavi A.
Published: May 2008

The genetic structure of the alcohol dehydrogenase (ADH) enzyme complex was studied by means of isozyme analysis among several common ash ( Fraxinus excelsior L.) provenances. We analysed if specific alloforms of locus ADH-B are selected under flooding stress caused by oxygen deprivation, since ADH is a fundamental enzyme of the plant metabolism under anoxia. This selection, if given, could therefore result in different ash ecotypes. Furthermore, genetic structures in the same provenances resulting from the analysis of four nuclear microsatellite markers are also discussed and compared with those resulting from the isozyme analyses to differentiate between adaptation and demographical processes. We found the highest value of genetic diversity at one of the two examined floodplains but did not find significant correlations between genotypes structures and flooding. The observed allele distributions can be mainly attributed to high human pressure and important seed transport events. These are regarded as the main forces shaping the actual genotype distributions rather than selection processes acting on locus ADH-B.
Differences in fibre properties in cloned Norway spruce (Picea abies)
Authors: Zubizarreta Gerendiain A. , Peltola H. , Pulkkinen P. , Jaatinen R. , Pappinen A.
Published: May 2008

In forest breeding programmes, growth has typically been used as a selection trait of prime importance in Norway spruce ( Picea abies (L.) Karst.), whereas less attention has been given to the wood and fibre characteristics. In the above context, we investigated phenotypic relationships between different fibre properties and growth and wood density traits in 20 cloned Norway spruce based on a clonal trial established in the 1970s in southeastern Finland. We found that fibre width showed, on average (2.9%), the lowest phenotypic variation followed by fibre wall thickness (3.4%), coarseness (5.5%), and fibre length (8.1%). All of the phenotypic correlations between the fibre properties were also positive (p < 0.05), ranging from moderate to strong, suggesting that selection for one trait could simultaneously affect the other traits. The phenotypic correlations, on average, were quite weak but positive between growth and fibre properties and slightly negative or weak positive between wood density and different fibre properties (p < 0.05). Individually, some of the clones showed negative correlation between growth traits and fibre length. As a result, selection for fibre properties alone could also reduce overall stem volume (or stem mass) and would not directly indicate wood density traits and vice versa.
Vegetation responses to stand structure and prescribed fire in an interior ponderosa pine ecosystemThis article is one of a selection of papers from the Special Forum on Ecological Studies in Interior Ponderosa Pine — First Findings from Blacks Mountain Interdisciplinary Research.
Authors: Zhang Jianwei , Ritchie Martin W. , Oliver William W.
Published: May 2008

A large-scale interior ponderosa pine ( Pinus ponderosa Dougl. ex P. & C. Laws.) study was conducted at the Blacks Mountain Experimental Forest in northeastern California. The primary purpose of the study was to determine the influence of structural diversity on the dynamics of interior pine forests at the landscape scale. High structural diversity (HiD) and low structural diversity (LoD) treatments were created with mechanical thinning on 12 main plots. Each plot was then split in half with one-half treated with prescribed fire. During the 5 year period after the treatments, the LoD treatments showed slightly higher periodic annual increments for basal area (BA) and significantly higher diameter increments than did the HiD treatments, although HiD carried twice as much BA as LoD did immediately after the treatments. Prescribed fire did not affect growth, but killed and (or) weakened some trees. No interaction between treatments was found for any variable. Stand density was reduced from the stands before treatments, but species composition did not change. Old dominant trees still grew and large snags were stable during the 5 year period. Treatments had minor impacts on shrub cover and numbers. These results suggest that ponderosa pine forest can be silviculturally treated to improve stand growth and health without sacrificing understory shrub diversity.
Bird occupancy and richness in ponderosa pine forests with contrasting forest structure and fire historyThis article is one of a selection of papers from the Special Forum on Ecological Studies in Interior Ponderosa Pine — First Findings from Blacks Mountain Interdisciplinary Research.
Authors: George T. Luke , Zack Steve
Published: May 2008

We compared the effects of two contrasting silvicultural treatments and prescribed fire on bird occupancy at Blacks Mountain Experimental Forest. Each silvicultural treatment was applied to two approximately 100 ha units within each of three blocks. Prescribed burning was applied to one-half of each silvicultural treatment in a split-plot design. Occupancy was estimated at eight points in each plot for 11 bird species and three foraging guilds (bark gleaners, woodpeckers, and foliage gleaners). The frequencies of species detections on the point counts were used to estimate species richness on each plot. Occupancy did not differ among treatments for any of the guilds. Four of the 11 bird species, the American robin ( Turdus migratorius L., 1766), the chipping sparrow ( Spizella passerina (Bechstein, 1798)), the white-breasted nuthatch ( Sitta carolinensis Latham, 1790), and the western tanager ( Piranga ludoviciana (A. Wilson, 1811)), showed responses to the treatments. Species richness did not differ between the silvicultural or the burn treatments. The general lack of response of the bird community to the silvicultural and burn treatments is likely a result of the relatively large size of the trees and snags retained on both silvicultural treatments, the low intensity of the prescribed burns, and the lack of a strong contrast in tree density between the silvicultural treatments.
Hypogeous fungal production in mature Douglas-fir forest fragments and surrounding plantations and its relation to coarse woody debris and animal mycophagy
Authors: Amaranthus Michael , Trappe James M. , Bednar Larry , Arthur David
Published: May 2008

Production of hypogeous fungi (truffles) in high-elevation, 180-year-old mature forest fragments of Pseudotsugamenziesii (Mirb.) Franco was compared with surrounding regenerated clearcuts ranging from 4 to 27 years since harvest at two study areas. Thirty pairs of plots, one of each pair in soil, the other in brown-cubical-rotted coarse woody debris (CWD), were searched for truffles in each stand during four periods; August and November 1990, and February and May 1991. Overall analysis of presence/absence of truffles using log-linear models revealed that CWD and mature forest status of stands each significantly influence truffle occurrence. Mature forest fragments had greater percent frequency of occurrence and truffle number and dry weight than did plantations. Truffle numbers and dry weight were 30 and 20 times greater, respectively, in mature forests than in plantations. The plantations did not differ significantly among each other for any parameter. CWD yielded higher numbers and biomass of truffles than soil in the mature forest, but production in plantations did not differ between substrates. The total dry weight of truffles in CWD exceeded that in soil by more than 10 times in mature forests. Of 21 truffle species found, 13 were only in the mature forest and 8 only under coarse woody debris. Forest practices that emphasize the retention of mature trees and coarse woody debris promote the abundance and diversity of truffles, which are integral and functionally important members of forest ecosystems.
Reduction of Douglas-fir beetle infestation of high-risk stands by antiaggregation and aggregation pheromones
Authors: Ross Darrell W. , Daterman Gary E.
Published: May 2008

A combination of antiaggregation and aggregation pheromones was tested for protecting stands of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) at high risk for infestation by the Douglas-fir beetle (Dendroctonuspseudotsugae Hopkins). The antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), was applied in a bubble capsule formulation to the perimeter of 1-ha circular plots at a rate of 60 g/plot. Treated plots also had three or four clusters of four Lindgren funnel traps baited with frontalin, seudenol, 1-methylcyclohex-2-en-1-ol, and ethanol located outside of the plot but within 160 m of the boundary. Mean (±SE) accumulated catches in all traps per plot were 73 658 ± 19 721 Douglas-fir beetles and 12 892 ± 2 513 Thanasimusundatulus (Say), a predator of the Douglas-fir beetle. The mean percentage of Douglas-fir trees ≥20 cm DBH that were mass attacked was reduced by 80% within the treated plots compared with the untreated plots. However, there was an eightfold increase in the percentage of trees mass attacked in the area outside the treated plots in the vicinity of the funnel traps. The net effect of the treatment was to concentrate mass-attacked trees within a limited area outside of the protected stand. Our results indicate that Douglas-fir beetle antiaggregation and aggregation pheromones can be used effectively to reduce the probability of infestation in small, high-value stands.
Differential tolerance of coniferous species to the microbially produced herbicide bialaphos. I. Morphological and growth effects
Authors: Sy Mlkaĭlou , Jobidon Robert , Margolis Hank
Published: May 2008

Four species of boreal conifer seedlings used for reforestation in eastern Canada were tested for their tolerance to the microbially produced herbicide bialaphos under controlled conditions. The tolerance levels of white spruce (Piceaglauca (Moench) Voss), black spruce (Piceamariana (Mill.) B.S.R), Norway spruce (Piceaabies (L.) Karst.), and red pine (Pinusresinosa Ait.) were studied over two consecutive growing seasons using different morphological and growth criteria. Application rates were the equivalent of 0, 1.0, 1.5, 2.0, 2.5, and 3.0 kg active ingredient (bialaphos) per hectare in a 1400-L solution and were applied in July, August, or September. Survival rates were a linear function of the dose of bialaphos, but were greater than 95% for all treatments. Results indicated that there was no significant correlation between visible foliar injury and the amount of epicuticular wax on needles. There was also no significant correlation between visible foliar injury and initial seedling height. However, a significant negative correlation was observed between the degree of foliar injury and the relative growth rate following treatment. No additional foliar injury occurred during the second growing season. Doses of bialaphos that did not exceed the equivalent of 2.0 kg active ingredient per hectare had no effect on subsequent growth. Tolerance was greatest when the herbicide was applied in August and least when applied in July. These results, combined with the lower tolerance previously demonstrated for several species that compete with planted conifers in eastern Canada, suggest that bialaphos has a strong potential as an alternative to chemically synthesized herbicides for vegetation management in conifer plantations.
The use of mitotic index in seedling assessments
Authors: Krasowski Marek J. , Owens John N.
Published: May 2008

The daytime pattern of mitotic index (MI) (percent of apical cells undergoing mitosis) in the shoot apex of Piceaglauca (Moench) Voss (white spruce) containerized seedlings was examined and compared for five cultural treatments. From sowing in March until mid-July, all seedlings were grown under an extended, 23-h photoperiod in a common nursery culture. In mid-July, an array of photoperiod treatments was created, ranging from ambient photoperiod and temperature to different levels of short day length and ambient or controlled, constant temperature. Consistency of MI comparisons among the treatments at different specimen collection times was emphasized rather than treatment effects on MI. Specimens were collected four times a day on two dates: when most seedlings in all treatments were initiating bud scales and when most seedlings were initiating leaf primordia. Patterns of MI were different on each of these dates. It is shown that conclusions about treatment effects on MI can be influenced by the sampling protocol and analytical approach. End of the growing season studies of white spruce and P. glauca × Piceasitchensis (Bong.) Carr. (white × Sitka spruce hybrid) seedlings grown in a greenhouse culture showed that MI below 1% was well correlated with low (<25%) foliage damage, reasonably correlated with stem tissue damage, and not correlated with bud damage resulting from controlled freezer tests to −18 °C. It is concluded that the MI technique could be useful in lifting-date determination, but different MI thresholds must be established for southern, northern, or coastal seed sources. Monitoring MI was not a good alternative to using days to bud break (testing under forcing conditions) to determine bud dormancy status. However, mitotic reactivation of the apical meristem in seedlings overwintering in a nursery bed occurred earlier in the spring than visible signs of growth reactivation (bud swelling and bud break). Studies of growth resumption of western red cedar (Thujaplicata Donn) seedlings in winter revealed that this species would be considered quiescent if tested under a long photoperiod, while under a short photoperiod growth resumption was much slower in early than in mid- and late winter.
Effect of drought stress and infestation by the balsam woolly adelgid (Homoptera: Adelgidae) on abnormal wood production in Fraser fir
Authors: Hollingsworth Robert G. , Hain Fred P.
Published: May 2008

Fraser fir (Abiesfraseri (Pursh) Poir.) seedlings were artificially infested with balsam woolly adelgid, Adelgespiceae (Ratz.), then subjected to drought-stress treatments. Infestation caused a distinct swelling in the main stem, caused by the accumulation of abnormal wood (i.e., "rotholz"). As expected, drought stress reduced diameter growth in the main stem. However, the reduction in wood increment caused by drought stress was relatively small for infested seedlings as compared with uninfested seedlings, owing to the production of rotholz. This implies that infested trees expend considerable energy and nutrients for the production of poorly functioning wood even during periods of stress. The implications of this research for interpreting patterns of tree mortality in the southern Appalachian Mountains are discussed.
Two hundred year variation of southern red spruce radial growth as estimated by spectral analysis: Comment
Authors: McLaughlin S.B. , Blasing T.J. , Downing D.J.
Published: May 2008

not available
Secondary ion mass spectroscopy (SIMS) in the analysis of elemental micropatterns in tree rings
Authors: Martin R.R. , Sylvester T. , Biesinger M.C.
Published: May 2008

Secondary ion mass spectroscopy (SIMS) has been used to examine elemental micropatterns in tree rings. Elevated potassium was detected in discrete rings, suggesting that this technique may have a wide application in dendrochronology.
THE DUAL EMBEDDING METHOD IN D = 3
Authors: ABREU E. M. C. , MENDES A. C. R. , NEVES C. , OLIVEIRA W. , TAKAKURA F. I. , XAVIER L. M. V.
Published: May 2008

Improving the beginning steps of a previous work, we settle the dual embedding method (DEM) as an alternative and efficient method for obtaining dual equivalent actions also in D = 3. We show that we can obtain dual equivalent actions which were previously obtained in the literature using the gauging iterative Noether dualization method (NDM). We believe that, with the arbitrariness property of the zero mode, the DEM is more profound since it can reveal a whole family of dual equivalent actions. The result confirms the one obtained previously which is important since it has the same structure that appears in the Abelian Higgs model with an anomalous magnetic interaction.
FROM GRAVITONS TO GRAVITY: MYTHS AND REALITY
Authors: PADMANABHAN T.
Published: May 2008

There is a general belief, reinforced by statements in standard textbooks, that: (i) one can obtain the full nonlinear Einstein theory of gravity by coupling a massless, spin 2 field hab self-consistently to the total energy–momentum tensor, including its own; (ii) this procedure is unique and leads to Einstein–Hilbert (EH) action; and (iii) it uses only standard concepts in Lorentz-invariant field theory and does not involve any geometrical assumptions. After providing several reasons why such beliefs are suspect — and critically re-examining several previous attempts — we provide a detailed analysis aimed at clarifying the situation. First, we prove that it is impossible to obtain the EH action, starting from the standard action for gravitons in linear theory and iterating repeatedly. This result follows from the fact that EH action has a part (viz. the surface term arising from second derivatives of the metric tensor) which is nonanalytic in the coupling constant, when expanded in terms of the graviton field. Thus, at best, one can only hope to obtain the remaining, quadratic, part of the EH Lagrangian (viz. the Γ2 Lagrangian) if no additional assumptions are made. Second, we use the Taylor series expansion of the action for Einstein's theory, to identify the tensor [Formula: see text], to which the graviton field hab couples to the lowest order (through a term of the form [Formula: see text] in the Lagrangian). We show that the second rank tensor [Formula: see text] is not the conventional energy–momentum tensor Tab of the graviton and provide an explanation for this feature. Third, we construct the full nonlinear Einstein theory with the source being a spin 0 field, a spin 1 field or relativistic particles by explicitly coupling the spin 2 field to this second rank tensor [Formula: see text] order by order and summing up the infinite series. Finally, we construct the theory obtained by self-consistently coupling hab to the conventional energy–momentum tensor Tab order by order and show that this does not lead to Einstein's theory. The implications are discussed.
POSSIBLE POLARIZATION AND SPIN-DEPENDENT ASPECTS OF QUANTUM GRAVITY
Authors: AHLUWALIA D. V. , GRESNIGT N. G. , NIELSEN ALEX B. , SCHRITT D. , WATSON T. F.
Published: May 2008

We argue that quantum gravity theories that carry a Lie-algebraic modification of the Poincaré and Heisenberg algebras inevitably provide inhomogeneities that may serve as seeds for cosmological structure formation. Furthermore, in this class of theories one must expect a strong polarization and spin dependence of various quantum gravity effects.
THE INEQUALITY BETWEEN MASS AND ANGULAR MOMENTUM FOR AXIALLY SYMMETRIC BLACK HOLES
Authors: DAIN SERGIO
Published: May 2008

In this essay I first discuss the physical relevance of the inequality [Formula: see text] for axially symmetric (nonstationary) black holes, where m is the mass and J the angular momentum of the space–time. Then, I present a proof of this inequality for the case of one spinning black hole. The proof involves a remarkable characterization of the extreme Kerr black hole as an absolute minimum of the total mass. Finally, I conjecture about the physical implications of this characterization for the nonlinear stability problem for black holes.
CHILD UNIVERSE UV REGULARIZATION?
Authors: GUENDELMAN E. I.
Published: May 2008

It is argued that high energy density excitations, responsible for UV divergences in quantum field theories, including quantum gravity, are likely to be the source of child universes which carry them out of the original space–time. This decoupling prevents the high UV excitations from having any influence on physical amplitudes. Child universe production could therefore be responsible for UV regularization in quantum field theories which take into account gravitational effects. Finally, we discuss child universe production in the last stages of black hole evaporation, the prediction of the absence of trans-Planckian primordial perturbations, the connection with the minimum length hypothesis, and in particular the connection with the maximal curvature hypothesis.
THE ISRAEL THEOREM: WHAT IS NATURE TRYING TO TELL US?
Authors: HERRERA L.
Published: May 2008

We explore the possible physical consequences derived from the fact that the only static and asymptotically flat vacuum space–time possessing a regular horizon is the Schwarzschild solution (Israel theorem). If small deviations from the Schwarzschild metric are described by means of exact solutions to Einstein equations (as should be the case), then for very compact configurations, at the time scale at which radiatable multipole moments are radiated away, important physical phenomena should occur, as illustrated by some results on different solutions belonging to the Weyl class of static, axially symmetric solutions to the Einstein equations.
A NEW SPIN ON QUANTUM GRAVITY
Authors: JACKSON MARK G. , HOGAN CRAIG J.
Published: May 2008

We suggest that the (small but nonvanishing) cosmological constant, and the holographic properties of gravitational entropy, may both reflect unconventional quantum spin statistics at a fundamental level. This conjecture is motivated by the nonlocality of quantum gravity and the fact that spin is an inherent property of space–time. As an illustration we consider the "quon" model, which interpolates between Fermi and Bose statistics, and show that this can naturally lead to an arbitrarily small cosmological constant. In addition to laboratory tests, we briefly discuss the possible observable imprint on cosmological fluctuations from inflation.
NON-LOCAL INFLATION AROUND A LOCAL MAXIMUM
Authors: LIDSEY JAMES E.
Published: May 2008

It is shown that non-local, higher-derivative operators, which arise generically in string field theory, can act as additional sources of friction on the inflaton field as it rolls away from a maximum in its potential. Moreover, the cosmic dynamics can be quantified in terms of a local field theory, where the curvature of an effective potential has been suppressed. A prolonged phase of quasi-exponential expansion can therefore be realised with steep potentials that typically arise in particle physics models. We illustrate this effect within the context of p-adic string theory.
FALLING INTO A BLACK HOLE
Authors: MATHUR SAMIR D.
Published: May 2008

String theory tells us that quantum gravity has a dual description as a field theory (without gravity). We use the field theory dual to ask what happens to an object as it falls into the simplest black hole: the two-charge extremal hole. In the field theory description the wave function of a particle is spread over a large number of "loops," and the particle has a well-defined position in space only if it has the same "position" on each loop. For the infalling particle we find one definition of "same position" on each loop, but there is a different definition for outgoing particles and no canonical definition in general in the horizon region. Thus the meaning of "position" becomes ill-defined inside the horizon.
GRAVITY AS AN EMERGENT PHENOMENON
Authors: PADMANABHAN T.
Published: May 2008

There are strong reasons to believe that the gravitational interaction — described in terms of a metric on a smooth space–time — is an emergent, long wavelength phenomenon, like elasticity. I describe a concrete framework for realizing this paradigm against the backdrop of several recent results. In this perspective, quantum fluctuations of the microscopic degrees of freedom of the space–time lead to residual random displacements of any null surface. The latter can be described in terms of an effective theory using an action associated with the normal displacements of the null surfaces. Extremizing this action leads to an equation determining the background geometry. The resulting theory is Einstein gravity at the lowest order with the Lanczos–Lovelock type quantum corrections. The metric is not a dynamical variable in this approach and gravity arises as a coarse-grained statistical feature of an underlying microscopic theory.
QUANTUM CONDENSATES IN EXTREME GRAVITY: IMPLICATIONS FOR COLD STARS AND DARK MATTER
Authors: SILVERMAN M. P.
Published: May 2008

Stable end-point stars currently fall into two distinct classes — white dwarfs and neutron stars — differing enormously in central density and radial size. No stable cold dead stars are thought to span the intervening densities or have masses beyond ~2–3 solar masses. I show, however, that the general-relativistic condition of hydrostatic equilibrium augmented by the equation of state of a neutron condensate at 0 K generates stable sequences of cold stars that span the density gap and can have masses well beyond prevailing limits. The radial sizes and mass limit of each sequence are determined by the mass and scattering length of the composite bosons. Solutions for hypothetical bosons of ultrasmall mass and large scattering length yield huge self-gravitating systems of low density, resembling galactic dark matter halos.
CELESTIAL OPTICAL INTERFEROMETRY: A NEW TOOL FOR ULTRAHIGH PRECISION STUDIES IN GRAVITY
Authors: UNNIKRISHNAN C. S. , GILLIES G. T.
Published: May 2008

The tremendous progress in the science and technology of timing devices and laser sources has reached a stage where their stability and coherence are sufficient for implementing unbalanced interferometers over a length scale exceeding the Earth–Moon distance. This opens up the possibility of optical homodyne interferometry over such distances, either to the Moon or to artificial satellites that are at large distances from the Earth. The precision of the measurement of changes in the orbital distance would increase by a factor of 104 or more, enabling new ultrahigh precision tests of the equivalence principle, study of gravitomagnetism, and of subtle gravitational phenomena, including the constancy of the gravitational constant and possible gravitational expansion of space. It would enable geodesy and tide studies with unprecedented precision. Such interferometers would also be useful for the detection and study of low frequency gravitational waves.
RESUMMED QUANTUM GRAVITY
Authors: WARD B. F. L.
Published: May 2008

We present the current status of the new approach to quantum general relativity based on the exact resummation of its perturbative series as this series was formulated by Feynman. We show that the resummed theory is UV-finite and we present some phenomenological applications as well.
GRAVITATIONAL ENERGY AND COSMIC ACCELERATION
Authors: WILTSHIRE DAVID L.
Published: May 2008

Cosmic acceleration is explained quantitatively, as an apparent effect due to gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. "Dark energy" is a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localized, namely gradients in the energy due to the expansion of space and spatial curvature variations in an inhomogeneous universe. A new scheme for cosmological averaging is proposed which solves the Sandage – de Vaucouleurs paradox. Concordance parameters fit supernova luminosity distances, the angular scale of the sound horizon in the CMB anisotropies, and the effective comoving baryon acoustic oscillation scale seen in galaxy clustering statistics. Key observational anomalies are potentially resolved, and unique predictions made, including a quantifiable variance in the Hubble flow below the scale of apparent homogeneity.
THE RETURN OF A STATIC UNIVERSE AND THE END OF COSMOLOGY
Authors: KRAUSS LAWRENCE M. , SCHERRER ROBERT J.
Published: May 2008

We demonstrate that as we extrapolate the current ΛCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.
TESTING MARSHALLIAN AND WALRASIAN INSTABILITY WITH AN AGENT-BASED MODEL
Authors: POSADA MARTA , HERNÁNDEZ CESÁREO , LÓPEZ-PAREDES ADOLFO
Published: May 2008

Do the Marshallian and Walrasian models have a firm foundation on micromotives, or are they just macroabstractions that we could dispense in microeconomics? Previous evidence from experimental economics with human subjects in continuous double auction markets shows that, if the supply is downward-sloping or the demand is upward-sloping, the Marshallian stability model captures the observed phenomena but the Walrasian does not. But, of course, in human subjects experiments the basic question of what the human agents' behavior is remains open. We build an artificial agent-based model to show that the path of convergence needs more intelligence than the zero-intelligence framework. Results from experimental economics with human agents reproduced with artificial agents at a low cost and with an increase in the reliability of the experiment. Not only the existence but also the computation of the stability is relevant. These results cast a shadow on the interest of both instability concepts in economic theory.
REPUTATION FOR INNOVATING SOCIAL NETWORKS
Authors: CONTE ROSARIA , PAOLUCCI MARIO , SABATER-MIR JORDI
Published: May 2008

Reputation is a fundamental instrument of partner selection. Developed within the domain of electronic auctions, reputation technology is being been imported by other applications, from social networks to institutional evaluation. Its impact on trust enforcement is uncontroversial and its management is of primary concern for entrepreneurs and other economic operators.

In this paper, we will briefly report on simulation-based studies of the role of reputation as a more tolerant form of social capital than familiarity networks. Whereas the latter exclude nontrustworthy partners, reputation is a more inclusive mechanism on which larger and more dynamic networks are constructed. After the presentation of the theory of reputation developed by the authors in the last decade, a computational system (REPAGE) for forming and exchanging reputation information will be presented and findings from experimental simulations recently run on this system will be resumed. Final remarks and ideas for future work will conclude the paper.
MEASURING SOLIDARITY IN AGENT-BASED MODELS OF RESOURCE SHARING SITUATIONS
Authors: BOTS PIETER W. G. , BARRETEAU OLIVIER , ABRAMI GERALDINE
Published: May 2008

In this paper we present a first attempt to represent the social behavior of actors in a resource sharing context in such a way that different forms of solidarity can be detected and measured. We expect that constructing agent-based models of water-related interactions at the interface of urban and rural areas, and running social simulations to study the occurrence and consequences of solidary behavior, will produce insights that may eventually contribute to water and land resource management practice. We propose a typology for solidary behavior, present the agent-based architecture that we are using, show some illustrative results, and formulate some questions that will guide our future work.
EDITORIAL
Authors: AMBLARD FRÉDÉRIC , JAGER WANDER
Published: May 2008

This special issue of Advances in Complex Systems presents a collection of selected papers of the 4th Conference of the European Social Simulation Association held in Tolulouse, France on 10–14 September 2007.