bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil moisture reduces belowground heat flux and soil temperatures under a burning fuel pile
Authors: Frandsen William H. , Ryan Kevin C.
Published: November 2007

A direct comparison of temperatures and heat loads was made between simulated duff-covered (~2 cm) and uncovered mineral soil beneath a burning fuel pile. Temperatures were recorded in the duff, at the duff – mineral soil interface, and at 1-cm intervals downward to a depth of 4 cm. Covering reduced the peak temperatures about 200 °C in dry mineral soil. Wet mineral soil covered with wet duff experienced a temperature reduction of over 500 °C. Temperatures in wet mineral soil did not exceed 90 °C and the heat load into the wet mineral soil was, on the average, 20% of the heat load into the dry mineral soil. Land managers wanting to minimize mortality of existing plants or loss of soil organics should strive to burn when mineral soils are approaching saturation near the surface.
Wood resources and availability as determinants of the supply of timber
Authors: Styrman Mattias , Wibe Sören
Published: November 2007

This paper presents a supply and demand model for the production of timber. Factors affecting supply for each country are (i) product price, (ii) wood density, and (iii) amount of forest resources. Demand (for each country) is modelled from per capita consumption and explaining variables are (i) product price and (ii) per capita income. The system is estimated in its reduced form with data from 35 countries. The study produced three main conclusions. (i) Production of timber is roughly proportional to each country's forest resource, (ii) The overall demand elasticity with respect to per capita income is negative, which implies that total demand for wood declines as income increase. This is explained by the fact that the demand for fuelwood declines faster than the demand for industrial roundwood increase when per capita income increase. (iii) The supply elasticity with respect to cost is around 2, which implies that an increase in cost by 1% might be expected to lead to decline in the supply of timber by 2%.
Larch litter and nitrogen availability in mixed larch–spruce stands. II. A comparison of larch and spruce litters as a nitrogen source for Sitka spruce seedlings
Authors: Carlyle J. C. , Malcolm D. C.
Published: November 2007

On deep peat sites where available N levels are low, the growth and N status of Sitka spruce are improved when the species is grown in mixed larch–spruce (75/25%) stands. It has been suggested that larch litter mineralizes more readily than other coniferous litters, thereby increasing N availability in mixed stands. However, while larch litter was demonstrated to release N more readily than spruce litter, the amount of N contained in larch litter fall seems too low to be of quantitative importance.
A growth model based on the self-thinning rule
Authors: Smith N. J. , Hann D. W.
Published: November 2007

A two-staged stand growth model is developed to describe the relationship between biomass or volume and numbers of stems in even-aged, monospecific plant populations undergoing self-thinning. The model is tested on red alder (Alnusrubra Bong.) seedlings and red pine (Pinusresinosa Ait.) stands grown over a range of site qualities and initial spacings. First, survival rate is modelled as a Weibull distribution. This is then fit to an analytical size–density model to give growth estimates. Crown closure is estimated to occur at a relative density of 0.09 for red alder, while initial mortality is estimated to occur at a relative density of 0.12 for red pine. Net stand growth rates peaked at a relative density of 0.54 for red alder biomass and from relative densities from 0.40 (widest initial spacing) to 0.55 (densest initial spacing) for red pine total stem volume. Site quality merely shifted the magnitude of these relationships. The model adds a dynamic component to the self-thinning rule and also generalizes and extends the rule to stand development between crown closure and the self-thinning asymptote.
A strategy for concurrently monitoring the plant water potentials of spatially separated forest ecosystems
Authors: Strong W. L , Roi G. H. La
Published: November 2007

A technique for estimating plant water potentials in plant communities was used in six forest stands representing a jack pine (Pinusbanksiana Lamb.) and a black spruce (Piceamariana (Mill.) B.S.P.) successional sequence. A set of 31 plants composed of 16 species were measured at 4-day intervals from early May to late August 1982. The six stands had similar patterns of summer plant water potentials with greatest differentiation among species occurring during periods of maximum water stress. Plant water potentials varied more in jack pine stands on sand than in black spruce stands on organic soil. Shallow-rooted ericaceous and (or) evergreen species (e.g., Vacciniummyrtilloides Michx., Vacciniumvitis-idaea L., and Pyrolaasarifolia Michx.) had the widest range of water potentials during summer, whereas deep-rooted Alnuscrispa (Ait.) Pursh had the narrowest range. Maximum morning (0700) water potentials reached−3.1 MPa. All species had fine roots (<2 mm) within the upper 20 cm of the soil, but some species of the Jack Pine Series had roots to 230 cm depth. Soil moisture was usually more available in the upper 20 cm and below 60 cm in mineral soils; the lower amount of soil moisture at middle depths resulted from depletion by plants and lack of downward percolation of precipitation in 1982.
Differential growth of individual components of trees and their interrelationships
Authors: Eis S.
Published: November 2007

The growth of six Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), eight western hemlock (Tsugaheterophylla (Raf.) Sarg.), and eight western red cedar (Thujaplicata Donn.) trees was studied using standard stem-analysis techniques. Trees standing side by side had similar height and diameter increment patterns, i.e., high and low increments in identical years. With increasing distance, this similarity rapidly decreased even on identical forest sites. On different sites, the patterns were different, often opposite. The length increment pattern on branches was similar to that shown by stem height increment only on four to five top whorls. On exposed branches the average decrease of both diameter and length increments was slow and fluctuated widely from one year to another. On shaded branches the decrease in increment was rapid and smooth. Growth of roots was very irregular and uncorrelated one with another; while some grew rapidly in length in some years, others in the same root system grew slowly or not at all. The radial increments and the increment patterns of structural roots were similar to the pattern in the stem, but long, ropelike lateral roots had their own independent growth patterns dissimilar to those of any other part of the tree.
Development and growth of even-aged stands of Douglas-fir and grand fir
Authors: Larson Bruce C.
Published: November 2007

Stand development patterns and growth rates of even-aged mixed stands of Douglas-fir (Pseudotsugamensiesii Mirb. Franco) and grand fir (Abiesgrandis Dougl. Lindl.) were investigated by stand reconstruction in eastern Washington. Although Douglas-fir dominated the stands early, grand fir of the same age eventually overtook the tallest Douglas-firs. Dominant trees of both species were found to have highly variable taper form (based on basal area to height ratios), although a linear relationship existed in other crown classes. Stem volume growth rates were determined by reconstructing past diameters and heights and were found comparable to site class IV Douglas-fir in western Washington. Intensive management, especially planting and thinning, could improve upon the observed mean annual increments of 800 board feet per acre at 80 years of age.
Relationships between shoot length and shoot length components in Douglas-fir and blue spruce
Authors: Bongarten Bruce
Published: November 2007

Number of stem units (NSU) and mean stem unit length (MSUL) were examined for their influence on first-order lateral shoot length in a 14-year-old, range-wide provenance test of interior Douglas-fir and an 8-year-old, range-wide provenance–progeny test of blue spruce. The degree to which each component influenced variation in shoot length depended on (i) the population, (ii) the level of population structure (between and within provenances), and (iii) whether phenotypic, genotypic, or environmental data were considered. In Douglas-fir, northern and southern trees were consistently different in MSUL. However, in northern and southern Douglas-fir considered separately and in blue spruce, provenance differences in shoot length were primarily due to variation in NSU. Within provenances, phenotypic variation in shoot length was caused equally by MSUL and NSU in both Douglas-fir and blue spruce. However, in blue spruce, genetic variation was mostly due to the MSUL component, while environmental variation was caused primarily by the NSU component. As a result, MSUL had a higher heritability than NSU. MSUL was also well correlated with tree height (within provenances) while NSU was not. MSUL and NSU were negatively correlated among provenance means, within provenances, on a phenotypic, genetic, or environmental basis. This limits the usefulness of these components as selection criteria and emphasizes the need for better understanding of shoot growth physiology to identify independent sources of variation in growth rate.
Biomass of tropical tree plantations and its implications for the global carbon budget
Authors: Brown Sandra , Lugo Ariel E. , Chapman Jonathan
Published: November 2007

To determine the present and future role of tropical tree plantations in the global carbon budget, data on rates of plantation establishment and their commercial volumes, by species groups and age-classes, were gathered and converted to biomass and ultimately to carbon fluxes. The rate of plantation establishment has increased dramatically since the 1940's, resulting in an area in 1980 of about 11 × 106 ha with more than 60% of this area planted during the last decade. Total biomass of plantations is estimated to range from 0.65 × 109 to 2.22 × 109 t or about 1% of the biomass of natural forests. Most of the biomass (79%) is in the 6- to 30-year-old plantations. We estimate that tropical plantations are a small sink of atmospheric carbon of 0.03–0.11 × 109 t C/year, most of which occurs in the two youngest age-classes. Although this flux is small, it may be sufficient to balance the small source of carbon from harvesting forests and other land-use changes in the temperate zone.
Artificial inoculation of Populus hybrids with Septoriamusiva
Authors: Long R. , Bowersox T. W. , Merrill W.
Published: November 2007

Cuttings of Populus hybrid clone NE-388 (Populusmaximowiczii Henry × Populustrichocarpa Torr & Gray) were inoculated with mycelium of Septoriamusiva Peck at three potential infection courts. Cankers resulting from inoculations at stipule – petiole excision wounds and bud excision wounds developed within 17–30 and 18–22 days, respectively. Only one canker resulted from 30 nonwound lenticel inoculations. Young trees (15 and 16 weeks from planting date) developed more cankers than older trees (18 weeks from planting date). Trees atomized with conidia of S. musiva did not develop cankers; however, leaf spots developed 18–23 days after inoculation.
Mansonone E and F accumulation in Ulmuspumila resistant to Dutch elm disease
Authors: Duchesne L. C. , Hubbes M. , Jeng R. S.
Published: November 2007

The presence of mansonones E and F in Ulmuspumila L. seedlings was determined 1, 2, 3, 5, 7, and 9 weeks after inoculation with aggressive and nonaggressive strains of Ophiostomaulmi (Buisman) Nannf. Mansonones E and F were accumulated in greater quantities by the seedlings inoculated with either strain than the seedlings inoculated with autoclaved distilled water or the control seedlings. No difference in mansonone induction was observed between the aggressive and the nonaggressive strain. Mansonones E and F accumulated until 2 weeks after inoculation and subsequently declined. Both aggressive and nonaggressive strains were recovered in the same frequencies from the inoculation wounds. The accumulation of mansonones E and F by U. pumila is discussed in regard to resistance to Dutch elm disease.
Biomass estimation equations for Norway spruce in New York
Authors: Jokela E. J. , Gurp K. P. Van , Briggs R. D. , White E. H.
Published: November 2007

Biomass estimation equations for plantation-grown Norway spruce (Piceaabies (L.) Karst.) were developed from data of 30 sample trees and expressed using the linear form of the following allometric equation: In Y = b0 + b1 ln X + ln ε, where Y is dry weight and X is dbh or D2H. The accuracy of the equations for biomass estimates were ranked as follows: total tree > stem wood > stem bark > foliage > live branches > dead branches. Diameter alone was a strong predictor of biomass and the addition of height to the model only slightly reduced the standard error of the estimate for the stem component equations. Comparison of results to equations developed in Sweden showed similarity in predictions for total biomass, but also showed disparity in predictions for individual tree components. Factors that influence tree morphology and distribution patterns of dry matter accumulation, such as stocking and site quality, may be responsible for these differences.
Somatic embryogenesis in tissue cultures of Liriodendrontulipifera
Authors: Merkle S. A. , Sommer H. E.
Published: November 2007

Tissue cultures of yellow poplar (Liriodendrontulipifera L.) were initiated from immature and mature zygotic embryos. Nodular embryogenic callus developed from a low percentage of the cultures initiated from immature embryos on solid media supplemented with 2,4-dichlorophenoxyacetic acid, 6-benzyladenine, and casein hydrolysate. Embryoids differentiated from these culture lines within 1 month following transfer of embryogenic callus to hormone-free solid media. Although most embryoids appeared abnormal, embryoids with well-formed cotyledons and radicles were capable of developing into normal plantlets.
The effect of water table depth on white spruce (Piceaglauca) seedling growth in association with the marsh reed grass (Calamagrostiscanadensis) on wet mineral soil
Authors: Rivard Paul G. , Woodard Paul M. , Rothwell Richard L.
Published: November 2007

The effect of water table depth (10, 20, and 40 cm) in association with marsh reed grass (CalamagrostisCanadensis (Michx.) Beauv.) on white spruce (Piceaglauca (Moench) Voss) 2 + 0 seedling survival and growth was tested over a 5-month period. All spruce seedlings grown alone survived, whereas, 16.7% of the trees died when grown with reed grass. The root weight and total weight of spruce seedlings and marsh reed grass were significantly affected by the water table depth. The weight of both components increased as the water table decreased. Over 80% of the roots by weight for both species were found in the upper 10 cm of the soil profile regardless of water table depth. The presence of marsh reed grass significantly affected the growth of spruce seedlings. The nutrient concentration of the white spruce foliage was significantly affected by water table depths and the presence of grass.
Landscape ecosystems of disturbed oak forests of southeastern Michigan, U.S.A.
Authors: Archambault Louis , Barnes Burton V. , Witter John A.
Published: November 2007

An ecological multifactor approach was used to identify and describe oak ecosystem types in highly disturbed landscapes and fragmented forests in an area of over 19 000 km2 in southeastern Michigan, United States. Eleven upland ecosystems and 1 wetland ecosystem were identified in the field using reconnaissance, plot sampling, and test mapping. Each ecosystem type was a characteristic combination of physiography, soil, and climax vegetation (overstory and ground-cover vegetation). The ecological approach emphasized physiographic and soil factors because of the disturbed state of the vegetation. Of 222 species of ground-cover vegetation, only 68 were used in forming the 13 ecological species groups. White oak (Quercusalba L.) exhibited the largest ecological amplitude of the three major oak species; it occurred on dry to mesic sites. Red oak (Q. rubra L.) occurred on dry-mesic to mesic sites, and black oak (Q. velutina Lam.) was restricted to dry sites. Discriminant analysis was used to examine the distinctness of the upland ecosystems and to compare the error rates of different ecosystem components. The misclassification rates obtained by using all ecosystem components (physiography, soil, ecological species groups, and overstory vegetation) were the lowest: 20% in highly dissected terrain and 34% in flat to gently rolling terrain. However, results obtained with physiography–soil and ecological species group variables were nearly as good as results that added the overstory vegetation. More overlap among ecosystem types and higher misclassification rates were found than in ecosystems of old-growth forests of northern Michigan and oak forests in southwestern Wisconsin where similar methods were used. Nevertheless, for the highly disturbed forests of southern Michigan, the ecological, multifactor landscape approach is a useful and effective method of identifying, describing, and mapping ecosystem types.
Modeling inputs of large woody debris to streams from falling trees
Authors: Sickle John Van , Gregory Stanley V.
Published: November 2007

A probabilistic model predicts means and variances of the total number and volume of large woody debris pieces falling into a stream reach per unit time. The estimates of debris input are based on the density (trees/area), tree size distribution, and tree-fall probability of the riparian stand adjacent to the reach. Distributions of volume, length, and orientation of delivered debris pieces are also predicted. The model is applied to an old-growth coniferous stand in Oregon's Cascade Mountains. Observed debris inputs from the riparian stand exceeded the inputs predicted from tree mortality rates typical of similar nonriparian stands. Debris pieces observed in the stream were generally shorter, with less volume per piece, than those predicted by the model, probably because of bole breakage during tree fall. As a second application, predicted debris inputs from riparian management zones of various widths are compared with the input expected from an unharvested stand.
Effects of winter injury on basal area and height growth of 30-year-old red spruce from 12 provenances growing in northern New Hampshire
Authors: Wilkinson Ronald C.
Published: November 2007

Basal-area increment and height growth of 30-year-old red spruce (Picearubens Sarg.) from 12 rangewide provenances growing in a plantation in northern New Hampshire were measured for a 3-year period (1986 through 1988) in which severe and (or) frequent winter damage to needles occurred. Growth of uninjured trees and injured trees were compared. Basal-area increments were successively smaller for groups of trees arranged in increasing order of average needle damage as a portion of the upper crown and number of years that the trees were injured. A similar pattern was observed for height growth, but the effect of winter damage was not as great on height growth as on basal-area increment. Growth losses following winter injury, especially height growth, were much greater for trees in provenances classed as pure red spruce than for trees in provenances where introgressive hybridization with black spruce (Piceamariana (Mill.) B.S.P.) has been demonstrated. For pure red spruce populations, repeated injury in 3 successive years or a sustained average of 30% or more needle damage resulted in losses in basal-area increment and height growth of up to 59 and 30%, respectively. Basal-area growth of the most severely injured trees in New England - New York provenances was 63% less than that of uninjured trees. These results support the contention of others that winter injury could be an initiating or perpetuating factor in red spruce decline.
The influence of espacement on the growth and development of a lodgepole pine plantation
Authors: Johnstone W. D. , Pollack J. C.
Published: November 2007

Seedlings from two lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) provenances were planted at four square espacements of 1.8, 2.4, 3.0, and 3.7 m in the Sub-Boreal Spruce Zone of central British Columbia. Data for the first 20 years after planting were analyzed in terms of the entire stand and portions of it. Plantation espacement had a major effect on early growth and development. Wide spacings resulted in greater diameter increments and produced trees of larger bole and crown dimensions. Close spacings resulted in larger per-hectare stand values and smaller branch diameters.
Mating system variation among individual ramets in a Douglas-fir seed orchard
Authors: Erickson V. J. , Adams W. T.
Published: November 2007

Proportions of outcrossed progeny (ti) in five ramets of five clones with variable floral phenology and pollen production were investigated in a Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco) seed orchard. Estimates of ti[Formula: see text] were significantly heterogeneous among the five ramets, ranging in value from 0.50 to 1.07. Variation in [Formula: see text] corresponded well with variation among ramets in floral biology. Ramets that flowered much earlier than other individuals in the orchard and (or) had a high degree of synchrony in timing of male and female flowering produced the lowest [Formula: see text].
Assessing components of competition indices for young boreal plantations
Authors: MacDonald G. Blake , Morris Dave M. , Marshall Peter L.
Published: November 2007

not available
THERMODYNAMICS OF MODIFIED BLACK HOLES FROM GRAVITY'S RAINBOW
Authors: LING YI , LI XIANG , ZHANG HONGBAO
Published: November 2007

We study the thermodynamics of modified black holes proposed in the context of gravity's rainbow. A notion of intrinsic temperature and entropy for these black holes is introduced. In particular for a specific class of modified Schwarzschild solutions, their temperature and entropy are obtained and compared with those previously obtained from modified dispersion relations in deformed special relativity. It turns out that the results of these two different strategies coincide, and this may be viewed as a support for the proposal of deformed equivalence principle.
THERMO MINIMUM UNCERTAINTY STATE FOR FERMIONIC TFD THEORY
Authors: XU XUE-FEN , FAN HONG-YI
Published: November 2007

By analyzing the characters of Thermo Field Dynamics (TFD) that every annihilation operator f acting on real Hilbert space has an image [Formula: see text] acting on fictitious space we should choose [Formula: see text] and [Formula: see text], or their linear combination [Formula: see text], and [Formula: see text] for measuring Fermi field's fluctuation at finite temperature. As a consequence, the corresponding minimum uncertainty states are derived, which resembles the form of fermionic squeezed state. This work is the fermionic counterpart of Ref. 8 in which bosonic TFD's minimum uncertainty states are obtained.
GAUGE DEPENDENCE AMBIGUITY AND CHEMICAL POTENTIAL IN THERMAL U(1) THEORY
Authors: LOEWE M. , MENDIZABAL S. , SANTOS R. A.
Published: November 2007

In this paper we explore the dependence on the gauge-fixing condition of several quantities in the U(1) Higgs model at finite temperature and chemical potential. We compute the effective potential at the one-loop level, using a gauge-fixing condition that depends on μ and which allows to decouple the contributions of the different fields in the model. In this way we get the mass spectrum and the characterization of the phase transition, pointing out in each case how these quantities depend on the gauge-fixing parameter ξ. When μ vanishes, we agree with previous results if ξ=0. The gauge dependence problem is also analyzed from the perspective of the Nielsen identities.
ON THE NONSYMMETRIC PURELY AFFINE GRAVITY
Authors: POPŁAWSKI NIKODEM J.
Published: November 2007

We review the vacuum purely affine gravity with the nonsymmetric connection and metric. We also examine dynamical effects of the second Ricci tensor and covariant second-rank tensors constructed from the torsion tensor in the gravitational Lagrangian.
GLUINO AXION, NEUTRINO SEESAW, DYNAMICAL GAUGINO MASS, AND A≃0 SUPERSYMMETRY
Authors: MA ERNEST
Published: November 2007

In the axionic solution of the strong CP problem, fermions which transform under quantum chromodynamics (QCD) are required. In supersymmetry, by equating U (1)PQ with U (1)R, the natural candidates are the gluinos, as pointed out some years ago. A new specific implementation of this idea is proposed, linking the gluino axion scale to that of the canonical seesaw mechanism for neutrinos. Gaugino masses are generated dynamically and the A term is predicted to be very small.
A uniform type structure for secure information flow
Authors: Honda Kohei , Yoshida Nobuko
Published: November 2007

The π-calculus, a calculus of mobile processes, can compositionally represent dynamics of major programming constructs by decomposing them into name passing. The present work reports our experience in using a linear/affine typed π-calculus for the analysis and development of type-based analyses for programming languages, focussing on secure information flow analysis. After presenting a basic typed calculus for secrecy, we demonstrate its usage by a sound embedding of the dependency core calculus (DCC) and the development of the call-by-value version of DCC. The secrecy analysis is then extended to stateful computation, for which we develop a novel type discipline for imperative programming language that extends a secure multi-threaded imperative language by Smith and Volpano with general references and higher-order procedures. In each analysis, the embedding gives a simple proof of noninterference.
A step towards unifying schedule and storage optimization
Authors: Thies William , Vivien Frédéric , Amarasinghe Saman
Published: November 2007

We present a unified mathematical framework for analyzing the tradeoffs between parallelism and storage allocation within a parallelizing compiler. Using this framework, we show how to find a good storage mapping for a given schedule, a good schedule for a given storage mapping, and a good storage mapping that is valid for all legal (one-dimensional affine) schedules. We consider storage mappings that collapse one dimension of a multidimensional array, and programs that are in a single assignment form and accept a one-dimensional affine schedule. Our method combines affine scheduling techniques with occupancy vector analysis and incorporates general affine dependences across statements and loop nests. We formulate the constraints imposed by the data dependences and storage mappings as a set of linear inequalities, and apply numerical programming techniques to solve for the shortest occupancy vector. We consider our method to be a first step towards automating a procedure that finds the optimal tradeoff between parallelism and storage space.
Ontology visualization methods—a survey
Authors: Katifori Akrivi , Halatsis Constantin , Lepouras George , Vassilakis Costas , Giannopoulou Eugenia
Published: November 2007

Ontologies, as sets of concepts and their interrelations in a specific domain, have proven to be a useful tool in the areas of digital libraries, the semantic web, and personalized information management. As a result, there is a growing need for effective ontology visualization for design, management and browsing. There exist several ontology visualization methods and also a number of techniques used in other contexts that could be adapted for ontology representation. The purpose of this article is to present these techniques and categorize their characteristics and features in order to assist method selection and promote future research in the area of ontology visualization.
Gaussian random number generators
Authors: Thomas David B. , Luk Wayne , Leong Philip H.W. , Villasenor John D.
Published: November 2007

Rapid generation of high quality Gaussian random numbers is a key capability for simulations across a wide range of disciplines. Advances in computing have brought the power to conduct simulations with very large numbers of random numbers and with it, the challenge of meeting increasingly stringent requirements on the quality of Gaussian random number generators (GRNG). This article describes the algorithms underlying various GRNGs, compares their computational requirements, and examines the quality of the random numbers with emphasis on the behaviour in the tail region of the Gaussian probability density function.
Strong accountability for network storage
Authors: Yumerefendi Aydan R. , Chase Jeffrey S.
Published: November 2007

This article presents the design, implementation, and evaluation of CATS, a network storage service with strong accountability properties. CATS offers a simple web services interface that allows clients to read and write opaque objects of variable size. This interface is similar to the one offered by existing commercial Internet storage services. CATS extends the functionality of commercial Internet storage services by offering support for strong accountability.

A CATS server annotates read and write responses with evidence of correct execution, and offers audit and challenge interfaces that enable clients to verify that the server is faithful. A faulty server cannot conceal its misbehavior, and evidence of misbehavior is independently verifiable by any participant. CATS clients are also accountable for their actions on the service. A client cannot deny its actions, and the server can prove the impact of those actions on the state views it presented to other clients.

Experiments with a CATS prototype evaluate the cost of accountability under a range of conditions and expose the primary factors influencing the level of assurance and the performance of a strongly accountable storage server. The results show that strong accountability is practical for network storage systems in settings with strong identity and modest degrees of write-sharing. We discuss how the accountability concepts and techniques used in CATS generalize to other classes of network services.
Contributing storage using the transparent file system
Authors: Cipar James , Corner Mark D. , Berger Emery D.
Published: November 2007

Contributory applications allow users to donate unused resources on their personal computers to a shared pool. Applications such as SETI@home, Folding@home, and Freenet are now in wide use and provide a variety of services, including data processing and content distribution. However, while several research projects have proposed contributory applications that support peer-to-peer storage systems, their adoption has been comparatively limited. We believe that a key barrier to the adoption of contributory storage systems is that contributing a large quantity of local storage interferes with the principal user of the machine.

To overcome this barrier, we introduce the Transparent File System (TFS). TFS provides background tasks with large amounts of unreliable storage—all of the currently available space—without impacting the performance of ordinary file access operations. We show that TFS allows a peer-to-peer contributory storage system to provide 40% more storage at twice the performance when compared to a user-space storage mechanism. We analyze the impact of TFS on replication in peer-to-peer storage systems and show that TFS does not appreciably increase the resources needed for file replication.
PARAID
Authors: Weddle Charles , Oldham Mathew , Qian Jin , Wang An-I Andy , Reiher Peter , Kuenning Geoff
Published: November 2007

Reducing power consumption for server-class computers is important, since increased energy usage causes more heat dissipation, greater cooling requirements, reduced computational density, and higher operating costs. For a typical data center, storage accounts for 27% of energy consumption. Conventional server-class RAIDs cannot easily reduce power because loads are balanced to use all disks, even for light loads.

We have built the power-aware RAID (PARAID), which reduces energy use of commodity server-class disks without specialized hardware. PARAID uses a skewed striping pattern to adapt to the system load by varying the number of powered disks. By spinning disks down during light loads, PARAID can reduce power consumption, while still meeting performance demands, by matching the number of powered disks to the system load. Reliability is achieved by limiting disk power cycles and using different RAID encoding schemes. Based on our five-disk prototype, PARAID uses up to 34% less power than conventional RAIDs while achieving similar performance and reliability.
Mesh Ensemble Motion Graphs
Authors: James Doug L. , Twigg Christopher D. , Cove Andrew , Wang Robert Y.
Published: November 2007

We explore the use of space-time cuts to smoothly transition between stochastic mesh animation clips involving numerous deformable mesh groups while subject to physical constraints. These transitions are used to construct
Mesh Ensemble Motion Graphs
for interactive data-driven animation of high-dimensional mesh animation datasets, such as those arising from expensive physical simulations of deformable objects blowing in the wind. We formulate the transition computation as an integer programming problem, and introduce a novel randomized algorithm to compute transitions subject to geometric nonpenetration constraints. We present examples for several physically based motion datasets, with real-time display and optional interactive control over wind intensity via transitions between wind levels. We discuss challenges and opportunities for future work and practical application.
Resolution-matched shadow maps
Authors: Lefohn Aaron E. , Sengupta Shubhabrata , Owens John D.
Published: November 2007

This article presents resolution-matched shadow maps (RMSM), a modified adaptive shadow map (ASM) algorithm, that is practical for interactive rendering of dynamic scenes. Adaptive shadow maps, which build a quadtree of shadow samples to match the projected resolution of each shadow texel in eye space, offer a robust solution to projective and perspective aliasing in shadow maps. However, their use for interactive dynamic scenes is plagued by an expensive iterative edge-finding algorithm that takes a highly variable amount of time per frame and is not guaranteed to converge to a correct solution. This article introduces a simplified algorithm that is up to ten times faster than ASMs, has more predictable performance, and delivers more accurate shadows. Our main contribution is the observation that it is more efficient to forgo the iterative refinement analysis in favor of generating all shadow texels requested by the pixels in the eye-space image. The practicality of this approach is based on the insight that, for surfaces continuously visible from the eye, adjacent eye-space pixels map to adjacent shadow texels in quadtree shadow space. This means that the number of contiguous regions of shadow texels (which can be efficiently generated with a rasterizer) is proportional to the number of continuously visible surfaces in the scene. Moreover, these regions can be coalesced to further reduce the number of render passes required to shadow an image. The secondary contribution of this paper is demonstrating the design and use of data-parallel algorithms inseparably mixed with traditional graphics programming to implement a novel interactive rendering algorithm. For the scenes described in this paper, we achieve 60--80 frames per second on static scenes and 20--60 frames per second on dynamic scenes for 512
2
and 1024
2
images with a maximum effective shadow resolution of 32,768
2
texels.
The jastadd extensible java compiler
Authors: Ekman Torbjörn , Hedin Görel
Published: November 2007

The JastAdd Extensible Java Compiler is a high quality Java compiler that is easy to extend in order to build static analysis tools for Java, and to extend Java with new language constructs. It is built modularly, with a Java 1.4 compiler that is extended to a Java 5 compiler. Example applications that are built as extensions include an alternative backend that generates Jimple, an extension of Java with AspectJ constructs, and the implementation of a pluggable type system for non-null checking and inferenc.

The system is implemented using JastAdd, a declarative Java-like language. We describe the compiler architecture, the major design ideas for building and extending the compiler, in particular, for dealing with complex extensions that affect name and type analysis. Our extensible compiler compares very favorably concerning quality, speed and size with other extensible Java compiler frameworks. It also compares favorably in quality and size compared with traditional non-extensible Java compilers, and it runs within a factor of three compared to javac.
Statistically rigorous java performance evaluation
Authors: Georges Andy , Buytaert Dries , Eeckhout Lieven
Published: November 2007

Java performance is far from being trivial to benchmark because it is affected by various factors such as the Java application, its input, the virtual machine, the garbage collector, the heap size, etc. In addition, non-determinism at run-time causes the execution time of a Java program to differ from run to run. There are a number of sources of non-determinism such as Just-In-Time (JIT) compilation and optimization in the virtual machine (VM) driven by timer-based method sampling, thread scheduling, garbage collection, and various.

There exist a wide variety of Java performance evaluation methodologies usedby researchers and benchmarkers. These methodologies differ from each other in a number of ways. Some report average performance over a number of runs of the same experiment; others report the best or second best performance observed; yet others report the worst. Some iterate the benchmark multiple times within a single VM invocation; others consider multiple VM invocations and iterate a single benchmark execution; yet others consider multiple VM invocations and iterate the benchmark multiple times.

This paper shows that prevalent methodologies can be misleading, and can even lead to incorrect conclusions. The reason is that the data analysis is not statistically rigorous. In this paper, we present a survey of existing Java performance evaluation methodologies and discuss the importance of statistically rigorous data analysis for dealing with non-determinism. We advocate approaches to quantify startup as well as steady-state performance, and, in addition, we provide the JavaStats software to automatically obtain performance numbers in a rigorous manner. Although this paper focuses on Java performance evaluation, many of the issues addressed in this paper also apply to other programming languages and systems that build on a managed runtime system.
Microphase
Authors: Xian Feng , Srisa-an Witawas , Jiang Hong
Published: November 2007

To date, the most commonly used criterion for invoking garbage collection (GC) is based on heap usage; that is, garbage collection is invoked when the heap or an area inside the heap is full. This approach can suffer from two performance shortcomings: untimely garbage collection invocations and large volumes of surviving objects. In this work, we explore a new GC triggering approach called
MicroPhase
that exploits two observations: (i) allocation requests occur in phases and (ii) phase boundaries coincide with times when most objects also die. Thus, proactively invoking garbage collection at these phase boundaries can yield high efficiency. We extended the HotSpot virtual machine from Sun Microsystems to support MicroPhase and conducted experiments using 20 benchmarks. The experimental results indicate that our technique can reduce the GC times in 19 applications. The differences in GC overhead range from an increase of 1% to a decrease of 26% when the heap is set to twice the maximum live-size. As a result, MicroPhase can improve the overall performance of 13 benchmarks. The performance differences range from a degradation of 2.5% to an improvement of 14%.
Component nextgen
Authors: Sasitorn James , Cartwright Robert
Published: November 2007

Developing a general component system for a statically typed, object-oriented language is a challenging design problem for two reasons. First, mutually recursive references across components are common in object-oriented programs-an issue that has proven troublesome in the context of component systems for functional and procedural languages. Second, inheritance across component boundaries can cause accidental method overrides. Our recent research shows that a component framework can be constructed for a nominally typed object-oriented language supporting first-class generic types simply by adding appropriate annotations, syntactic sugar, and component-level type-checking. The fundamental semantic building blocks for constructing, type-checking and manipulating components are provided by the underlying
first-class
generic type system. To demonstrate the simplicity and utility of this approach we have designed and implemented an extension of Java called Component NEXTGEN (CGEN). CGEN, which is based on the Sun Java 5.0
javac
compiler, is backwards compatible with existing Java binary code and runs on current Java Virtual Machines.

The primary contribution of this paper is a technical analysis of the subtle design issues involved in building a component framework for a nominally typed object-oriented language supporting first-class generics. In contrast to component systems for structurally typed languages, mutual recursion among components is accommodated in the type system and semantics without incorporating any special machinery. Our analysis includes a presentation of Core CGEN (CCG), a small, core language modeling the CGEN framework. It is based on Featherweight GJ and incorporates some ideas from MIXGEN. CCG adds the essential features to support components, but nothing more. Our discussion includes the type rules and semantics for CCG, as well as a proof of type safety.
User-changeable visibility
Authors: Ducasse Stéphane , Wuyts Roel , Bergel Alexandre , Nierstrasz Oscar
Published: November 2007

A trait is a unit of behaviour that can be composed with other traits and used by classes. Traits offer an alternative to multiple inheritance. Conflict resolution of traits, while flexible, does not completely handle accidental method name conflicts: if a trait with method
m
is composed with another trait defining a different method
m
then resolving the conflict may prove delicate or infeasible in cases where both versions of m are still needed. In this paper we present
freezeable traits
, which provide an expressive composition mechanism to support unanticipated method composition conflicts. Our solution introduces private trait methods
and
lets the class composer change method visibility at composition time (from public to private and vice versa). Moreover two class composers may use different composition policies for the same trait, something which is not possible in mainstream languages. This approach respects the two main design principles of traits: the class composer is empowered and traits can be flattened away. We present an implementation of freezable traits in Smalltalk. As a side-effect of this implementation we introduced private (early-bound and invisible) methods to Smalltalk by distinguishing object-sends from self-sends. Our implementation uses compile-time bytecode manipulation and, as such, introduces no run-time penalties.
Modular typestate checking of aliased objects
Authors: Bierhoff Kevin , Aldrich Jonathan
Published: November 2007

Objects often define usage protocols that clients must follow inorder for these objects to work properly. Aliasing makes itnotoriously difficult to check whether clients and implementations are compliant with such protocols. Accordingly, existing approaches either operate globally or severely restrict aliasing.

We have developed a sound modular protocol checking approach, based on typestates, that allows a great deal of flexibility in aliasing while guaranteeing the absence of protocol violations at runtime. The main technical contribution is a novel abstraction,
access permissions
, that combines typestate and object aliasing information. In our methodology, developers express their protocol design intent through annotations based on access permissions. Our checking approach then tracks permissions through method implementations. For each object reference the checker keeps track of the degree of possible aliasing and is appropriately conservativein reasoning about that reference. This helps developers account for object manipulations that may occur through aliases. The checking approach handles inheritance in a novel way, giving subclasses more flexibility in method overriding. Case studies on Java iterators and streams provide evidence that access permissions can model realistic protocols, and protocol checking based on access permissions can be used to reason precisely about the protocols that arise in practice.
Establishing object invariants with delayed types
Authors: Fahndrich Manuel , Xia Songtao
Published: November 2007

Mainstream object-oriented languages such as C# and Java provide an initialization model for objects that does not guarantee programmer controlled initialization of fields. Instead, all fields are initialized to default values (0 for scalars and
null
for non-scalars) on allocation. This is in stark contrast to functional languages, where all parts of an allocation are initialized to programmer-provided values. These choices have a direct impact on two main issues: 1) the prevalence of
null
in object oriented languages (and its general absence in functional languages), and 2) the ability to initialize circular data structures. This paper explores connections between these differing approaches and proposes a fresh look at initialization. Delayed types are introduced to express and formalize prevalent initialization patterns in object-oriented languages.
Tracking bad apples
Authors: Bond Michael D. , Nethercote Nicholas , Kent Stephen W. , Guyer Samuel Z. , McKinley Kathryn S.
Published: November 2007

Programs sometimes crash due to unusable values, for example, when Java and C# programs dereference null pointers and when C and C++ programs use undefined values to affect program behavior. A stack trace produced on such a crash identifies the effect of the unusable value, not its cause, and is often not much help to the programmer.

This paper presents efficient
origin tracking
of unusable values; it shows how to record where these values come into existence, correctly propagate them, and report them if they cause an error. The key idea is
value piggybacking
: when the original program stores an unusable value, value piggybacking instead stores origin information in the spare bits of the unusable value. Modest compiler support alters the program to propagate these modified values through operations such as assignments and comparisons. We evaluate two implementations: the first tracks null pointer origins in a JVM, and the second tracks undefined value origins in a memory-checking tool built with Valgrind. These implementations show that origin tracking via value piggybacking is fast and often useful, and in the Java case, has low enough overhead for use in a production environment.