bluuebunny/crossref_metadata_2025 huggingface dataset:
The Thermal Behavior of Oscillating Squeeze Films
Authors: Tichy J. A. , Smith R. N.
Published: November 2009

An analytical solution to the energy equation is provided for oscillating squeeze film flow, such as that which occurs in squeeze film damper bearings. Assumptions are: (a) the usual lubrication conditions for two-dimensional flow, (b) small oscillations, and (c) constant viscosity. Specific conditions are established for the latter assumption, which may be in force for stably operated squeeze film bearings. Relatively simple expressions are presented for the thermal performance variables (temperature field, average temperature, Nusselt number) for a variety of cases. The results are interesting from a heat transfer point of view in that the proper energy balance consists of dissipation, conduction, and storage terms, rather than convection terms as is usual in lubrication studies. Thus inferences drawn from other thermal analyses may be in error. Both average cross-film temperature rise and heat transfers are seen to increase from zero Pe´cle`t number and asympotically approach constant values. Due to the negligible convection conditions, the conventional definitions of bulk temperature, Nusselt number, and Pe´cle`t number are not appropriate. As a result of the thermal storage effect, interesting temporal phase-shift and temperature swing effects are exhibited.
Static Characteristics of Aerostatic Porous Rectangular Thrust Bearings With Offset Load
Authors: Singh K. C. , Rao N. S.
Published: November 2009

A theoretical analysis for the static characteristics of an aerostatic porous rectangular thrust bearing with an offset load, for both open and sealed end configurations, is presented considering three-dimensional flow in the porous matrix. Static characteristics for different operating parameters are calculated numerically and presented in dimensionless form as design charts. The effect of tilt is discussed.
Hydrodynamic Lubrication of Finite Slider Bearings: Effect of One Dimensional Film Shape, and Their Computer Aided Optimum Designs
Authors: Bagci C. , Singh A. P.
Published: November 2009

The effect of the film shape on the load carrying capacity of a hydrodynamically lubricated bearing has not been considered an important factor in the past. Flat-faced tapered bearing and the Raileigh’s step bearing of constant film thickness have been the primary forms of film shapes for slider bearing studies and design data developments. This article, by the computer aided numerical solution of the Reynolds equation for two dimensional incompressible lubricant flow, investigates hydrodynamically lubricated slider bearings having different film shapes and studies the effect of the film shape on the performance characteristics of finite bearings; and it shows that optimized bearing with film shapes having descending slope toward the trailing edge of the bearing has considerably higher load carrying capacity than the optimized flat-faced tapered bearing of the same properties. For example the truncated cycloidal film shape yields 26.3 percent higher load carrying capacity for Lz/Lx = 1 size ratio, and 44 percent higher for Lz/Lx = 1/2. The article then presents charts for the optimum designs of finite slider bearings having tapered, exponential, catenoidal, polynomial, and truncated-cycloidal film shapes, and illustrates their use in numerical bearing design examples. These charts also furnish information on flow rate, side leakage, temperature rise, coefficient of friction, and friction power loss in optimum bearings. Appended to the article are analytical solutions for infinitely wide bearings with optimum bearing characteristics. The computer aided numerical solution of the Reynolds equation in most general form is presented by which finite or infinitely wide hydrodynamically or hydrostatically lubricated bearings, externally pressurized or not, can be studied. A digital computer program is made available.
Hydrodynamic Sector Bearings as Circular Saw Guides
Authors: Mote C. D. , Schajer G. S. , Telle L. I.
Published: November 2009

Hydrodynamic sector bearings, which were arbitrarily oriented and tilted over a plane surface rotatng at constant angular velocity, were theoretically and experimentally investigated for thrust, pressure, friction, and lubricant flow. Such bearings have application in the positioning of circular saws and are termed saw guides. Four fundamental guide inclination states were defined, and a class of quasi-optimal designs, maximizing thrust intensity, were determined for each state. Experiments were conducted to support the theory.
Roughness Effects in Porous Circular Squeeze-Plates With Arbitrary Wall Thickness
Authors: Prakash J. , Tiwari K.
Published: November 2009

The stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effect of surface roughness on the response of a squeeze film between two circular plates when one plate has a porous facing. An exact solution is given for the film pressure and pressure in the bearing matrix, valid for arbitrary wall thickness. The results are presented in tabular form and a comparison is made with an earlier approximate analysis to determine the range of influencing parameters for which the approximate solution is acceptable.
Dynamic Analysis of Rupture in Thin Fluid Films. I—A Noninertial Theory
Authors: Pan C. H. T.
Published: November 2009

A noninertial theoretical model for the dynamics of film rupture has been formulated. Under the transient condition, movement of the rupture boundary is governed by the condition of flow continuity between the film flux and adhered film transport in the cavitation domain. The traditional Swift-Stieber condition for film breakup is shown to be valid upon reaching steady-state. Generalization is extended to allow consideration of two sliding surfaces and the pure squeeze-film. The possibility of subcavitation film pressure is shown to result in dry regions in the cavitation domain.
Ball Contact Locus in an Angular Contact Bearing
Authors: Kingsbury E. P.
Published: November 2009

The path of contact on the surface of a bearing ball is derived for pure spin and regular precession. Ball-race and ball-ball contacts are considered in a retainerless bearing. Track broadening and equatorial offset are found; quantitative experimental agreement is shown.
Film Formation and Flow Characteristics at the Inlet of a Starved Contact—Theoretical Study
Authors: Bonneau D. , Frene J.
Published: November 2009

The conditions of film formation are examined theoretically when starvation occurs. The analysis is for two-dimensional Newtonian flow and includes surface tension effects. Using an integral equation method, stream function solutions, velocity fields, pressure and shear stress distributions are calculated along and across the inlet zone of a sliding contact. The effect of surface tension and feeding thickness on the meniscus shape and on pressure buildup is studied in correlation with hydrodynamic effects. In all cases, pressure value lower than the gas pressure acting on the free boundary is found along the sliding surface. This depression value increases with an increase in viscosity or surface velocity. Owing to these results, a new interpretation of some published experimental data on starved contacts is proposed.
A Pitting Model for Rolling Contact Fatigue
Authors: Keer L. M. , Bryant M. D.
Published: November 2009

The interaction of a Hertzian contact, including friction, with an angled surface-breaking crack is studied with a view toward qualitatively explaining certain aspects of rolling contact fatigue. Cyclic loading and unloading of the surface crack, which is assumed to be embedded in a rolling wheel, is simulated by assuming that stresses having a Hertzian distribution travel across the half space such that one passage is equivalent to one cycle of rolling. By increasing the crack’s length and calculating the stress intensity factor, an estimate of the fatigue life can be determined.
Estimating the Severity of Shaft Vibrations Within Fluid Film Journal Bearings
Authors: McHugh J. D.
Published: November 2009

Proximity probes are being widely used in turbomachinery to measure the amplitude of shaft vibrations within fluid film bearings. There has been, however, little information available for judging the degree of severity of such vibrations. The present paper provides an analysis which correlates shaft vibration amplitude with some basic bearing parameters—allowable dynamic load on the bearing, its size, geometry, and operating conditions. Curves are provided for several bearing geometries which can be used for a rational estimate of allowable shaft vibration levels.
Wear of Steam Turbine Journal Bearings at Low Operating Speeds
Authors: Dufrane K. F. , Kannel J. W. , McCloskey T. H.
Published: November 2009

Worn steam turbine bearings were inspected and measured during overhaul periods to determine the extent and nature of the wear. Significant wear was found to exist on turbines using low turning gear speeds (10 rpm or less), and the wear occurred in spite of the presence of lift-pump systems. An analysis of the effect of geometric changes from wear on bearing lubrication at low speeds showed that a limited amount of wear may enhance lubrication. The analysis predicts that an optimum amount of wear exists beyond which the altered geometry would accelerate wear. Considerations were also made of the minimum speeds required to generate lubricant films sufficient to avoid bearing damage by the debris sizes typically found in turbine-generator lubricant systems.
Technique for Experimental Evaluation of Piston Ring—Cylinder Film Thickness
Authors: Dow T. A. , Schiele C. A. , Stockwell R. D.
Published: November 2009

A technique for estimating the piston ring film thickness by measuring the ring end gap has been developed. This paper discusses the details of the measurement technique, presents the results of a parametric study of the measured film thickness for unpressurized full-size diesel engine piston rings and compares those results with an analytical model. The film thickness is shown to depend upon the lubricant viscosity, the piston speed, the ring face profile and the quantity of lubricant available to the ring. The results of an analytical model, which assumes flooded lubrication conditions is also presented and the resulting film thicknesses are similar to those measured.
Analysis of Transitional and Fully Turbulent Plane Couette Flow
Authors: Missimer J. R. , Thomas L. C.
Published: November 2009

The two-dimensional, incompressible, fully-developed, turbulent plane Couette flow is a limiting case of circular Couette flow. As such, plane Couette flow analyses have been used in lubrication theory to analyze the lubrication flow in an unloaded journal bearings. A weakness of existing analyses, other than the turbulent burst analysis, is that they are not capable of characterizing the transitional turbulent regime. The objective of the proposed paper is to develop a model of the turbulent burst phenomenon for momentum in transitional turbulent and fully turbulent plane Couette flow. Model closure is obtained by specification of the mean turbulent burst frequency and, for moderate to high Reynolds numbers, by interfacing with classical eddy diffusivity models for the turbulent core. The analysis is shown to produce predictions for the mean velocity profile and friction factor that are in good agreement with published experimental data for transitional turbulent and fully turbulent flow. This approach to modeling the wall region involves a minimum level of empiricism and provides a fundamental basis for generalization. The use of the present analysis extends the applicability of plane Couette flow analysis in lubrication problems to the transitional turbulent regime.
The Effect of a Translating High Aspect Ratio Particle in a Plane Slider Bearing
Authors: Languirand M. T. , Tichy J. A.
Published: November 2009

An approximate solution of Stokes equations is presented to determine the pressure and velocity fields in an infinite slider bearing containing a two-dimensional high aspect ratio particle of arbitrary cross-section. The particle may translate in two directions as well as rotate about its centroid. The fluid field is divided into four regions: upstream, above, below, and downstream of the particle. The governing Stokes equations are applied to each region and solved through specific continuity requirements and pressure matching conditions. For illustrative purposes, this method of analysis is applied to a plane slider bearing containing a rectangular particle which can translate in one direction. Approximate solutions are given for the pressure and velocity fields. The solution reveals a pressure drop which develops in the pressure field at the particle location. The magnitude of this drop is shown to be dependent on a particle size, velocity, and location. It is shown that the particle has a major effect on the bearing pressure field when it is able to significantly obstruct the flow of the lubricant. To support the theoretical analysis, experimental research is performed. An experimental apparatus is used to measure the transient pressure in a slider bearing as a high aspect ratio two-dimensional rectangular particle is passed through the fluid film. The apparatus measures pressure at a particular location in the bearing and simultaneously measures the particle’s displacement with respect to its initial starting location. Results are given to demonstrate the effect of particle velocity on the pressure field in the bearing. The experimental results presented are in good agreement with analytical results obtained from the theoretical analysis.
A Three-Dimensional Analysis of Thermohydrodynamic Performance of Sector-Shaped, Tilting-Pad Thrust Bearings
Authors: Kim Kyung Woong , Tanaka Masato , Hori Yukio
Published: November 2009

The thermohydrodynamic performance of the bearing is analyzed, taking into account the three-dimensional variation of lubricant viscosity and density. The effect of pivot position and operating and environmental conditions on the performance is studied. The present analysis is compared with the isoviscous or the two-dimensional analysis, and is found to predict the bearing performance more accurately.
Dynamic Analysis of Turbulent Annular Seals Based On Hirs’ Lubrication Equation
Authors: Childs D. W.
Published: November 2009

Expressions are derived which define dynamic coefficients for high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions, and is modeled in this analysis by Hirs’ turbulent lubrication equations. Linear zeroth and first-order “short-bearing” perturbation solutions are developed by an expansion in the eccentricity ratio. The influence of inlet swirl is accounted for in the development of the circumferential flow field. Comparisons are made between the stiffness, damping, and inertia coefficients derived herein based on Hirs’ model and previously published results based on other models. Finally, numerical results are presented for interstage seals in the Space Shuttle Main Engine High Pressure Fuel Turbopump and a water pump.
High-Speed Motion Picture Camera Experiments of Cavitation in Dynamically Loaded Journal Bearings
Authors: Jacobson B. O. , Hamrock B. J.
Published: November 2009

It is important to know when and where cavitation occurs in bearings because cavitation has an effect on both the power loss and stability of the bearing. A bearing without cavitation can very well be unstable (vibrating) for the same working conditions where a cavitating bearing is stable. A high-speed camera was used to investigate cavitation in dynamically loaded journal bearings. The length-diameter ratio of the bearing, the speeds of the shaft and bearing, the surface material of the shaft, and the static and dynamic eccentricity of the bearing were varied. The results reveal not only the appearance of gas cavitation, but also the development of previously unsuspected vapor cavitation. Analysis is given to support the experimental findings for both gas and vapor cavitation.
Variational Formulation and Associated Algorithm for the Starved Finite Journal Bearing
Authors: Bayada G.
Published: November 2009

This paper is a contribution to the numerical treatment of the cavitation in a finite journal bearing when starvation takes place. A new variational form taking account the inlet flow parameter is given and allows us to compute rupture and reformation boundary together with the performances of the bearing via finite element method.
Predicted Performance Characteristics of Hybrid, Fluid-Equalized, Tilting-Pad Thrust Bearings
Authors: Shapiro W. , Graham R. , Anderson G.
Published: November 2009

The concept of a fluid-equalized, tilting-pad thrust bearing is presented. Load augmentation is introduced by external pressurization through the pad pivots. Performance characteristics were obtained for two different external hybrid supply systems. One system is completely independent of the equalizing system; the other utilizes a common supply and equalization system with separate control pads fixed to the support structure. The bearing retains (and may improve upon) the advantages of equalization and alignment inherent in hydrodynamic tilting-pad, leveling-link thrust bearings and permits significantly added load capacity.
Flying Characteristics of the “Zero-Load” Slider Bearing
Authors: White J. W.
Published: November 2009

One of the most critical elements making up a disk storage system is the air bearing interface located between the magnetic transducer and the disk surface on which data is stored and retrieved. The air film provided between the slider which houses the transducer and the disk serves to eliminate contact and wear of the solid surfaces and in addition must be extremely thin (on the order of 1/4 micron) in order to achieve a high density of data storage. Two of the most sought after properties of this lubricating film are a low generated load and high fluid stiffness. Low load allows the slider to be in contact with the disk when it is started and stopped, while high stiffness tends to provide a nearly uniform air bearing clearance which is important for reliable and efficient data storage and retrieval. The Zero-Load slider incorporates both low load and high stiffness in a single bearing. In this paper, the flying characteristics of the Zero-Load slider are discussed and its potential is explored. Numerical simulations which are presented for both static and dynamic operation indicate that the Zero-Load slider should be a strong contender for application in high performance disk files.
Design of Negative Pressure Slider for Magnetic Recording Disks
Authors: Kogure K. , Fukui S. , Mitsuya Y. , Kaneko R.
Published: November 2009

This paper reports on investigations of static and dynamic characteristics of a negative pressure slider for magnetic recording disks. The negative pressure slider is composed of two narrow pressure pads, as on a cylindrical slider, separated by a rather large reverse step region. Through a modified Reynolds equation, which considers slip flow effects, the static and dynamic pressure distributions are calculated by divergence formulation and a finite difference method. Using the calculated results, the optimum reverse step depth is clarified in terms of both dynamic characteristics and wear caused by starting and stopping in contact with the disk. With a 4.6 mm length, 3.2 mm total pad width and 4 μm reverse step depth, the negative pressure slider has six times the air film stiffness of a conventional light load slider. Experimental data concerning spacing versus reverse step depth and take-off characteristics for the negative pressure slider in submicron spacing region are in good agreement with the calculated results.
Roughness-Induced Dynamic Loading at Dry and Boundary-Lubricated Sliding Contacts
Authors: Soom A. , Kim C.
Published: November 2009

Measurements of instantaneous normal and frictional forces have been made at smoothly sliding hemispherical steel contacts under nominally dry and boundary-lubricated conditions. Normalized contact force fluctuations generated by surface irregularities are presented. Instantaneous frictional relations are characterized by performing spectral and transfer function computations on the measured signals. The qualitative dynamic frictional behavior is shown to be similar at dry and boundary-lubricated contacts. However, the magnitude of the dynamic loading is considerably reduced in the presence of lubrication. In both cases, an apparent time-varying frictional behavior is found to exist.
A Vibration Analysis of a Bearing/Cartridge Interface for a Fretting Corrosion Study
Authors: Elliott K. B. , Mabie H. H. , Furey M. J. , Mitchell L. D.
Published: November 2009

The relative motion between a ball bearing outer race and the bearing’s cartridge was investigated. The investigation was part of a larger program, the objective of which was to examine the important parameters influencing fretting corrosion in rolling element bearings. The bearing examined was a 320 size, deep grooved, ABEC 7 ball bearing used in a ship board motor-generator unit. Three axes of acceleration signatures were simultaneously recorded from the outer race and cartridge. These acceleration signatures were Fourier transformed, averaged, and integrated twice to obtain displacement frequency spectrums. Corresponding displacements were vectorially subtracted to produce the relative motion between the outer race and the cartridge. Two load cases (0 and 100 percent load) and two frequency ranges (15 to 500 Hz and 500 Hz to 10 kHz) are examined. The resulting relative motion spectrums were complex with the bearing’s forcing frequencies dominating the spectrums below 250 Hz and rotor imbalance causing the highest spectral component of relative displacement (4.30 μm).
Surface Topography Changes in Polymer-Metal Sliding—II
Authors: Jain V. K. , Bahadur S.
Published: November 2009

The variation in the surface topographical parameters for the case of sliding between high density polyethylene and poly(vinyl chloride) pin ends and a steel disk periphery was investigated. Sliding surface profile ordinate data were obtained at 2μm intervals using a data acquisition system, both along and perpendicular to the direction of sliding. A number of surface roughness parameters, viz., the r.m.s. and c.l.a. roughness, the slope, density, and radius of curvature of asperities, the standard deviation and distribution of profile ordinates, slopes, radii of curvatures and heights of asperities were calculated using a Fortran IV computer program. The analysis showed that the surface parameters undergo a marked variation during the early part of sliding, but the variation is statistically insignificant during the later part. It was found that the standard deviation of peak heights can be approximated by the r.m.s. surface roughness.
Investigation of the Effects of Initial Fluid Film Profile on Pumping Ring Operation
Authors: Smith P. J. , Keith T. G.
Published: November 2009

The effect of the initial fluid film profile on the pumping capacity of a pumping ring shaft seal has been investigated numerically. Linear, concave, convex and compound film shapes were considered. It was found that initial film shape has a pronounced effect on both the amount of fluid pumped and on the character of the flow pattern and pressure distribution within the film.
Stability of Unsymmetrical Rigid Rotor Supported by Self-Acting Gas-Lubricated Journal Bearings
Authors: Yoshimoto S. , Nakano Y.
Published: November 2009

In order to determine the threshold of instability for an unsymmetrical rigid rotor supported by two identical self-acting, plain-cylindrical gas journal bearings, a theoretical approach is made by the use of the quasi-static nonliner PH method. Influence of various parameters affecting the threshold of instability of the unsymmetrical rotor is experimentally shown and compared with the theoretical results. The experimental variables considered in this paper include bearing load, bearing length, bearing clearance, the axial deviation of the center of gravity from the center of the rotor span. Good agreement was obtained between the experimental and theoretical results.
The effect of interfraction prostate motion on IMRT plans: a dose‐volume histogram analysis using a Gaussian error function model
Authors: Chow James C. L. , Jiang Runqing , Markel Daniel
Published: November 2009

The Gaussian error function model, containing pairs of error and complementary error functions, was used to carry out cumulative dose‐volume histogram (cDVH) analysis on prostate intensity‐modulated radiation therapy (IMRT) plans with interfraction prostate motion. Cumulative DVHs for clinical target volumes (CTVs) shifted in the anterior‐posterior directions based on a 7‐beam IMRT plan were calculated and modeled using the Pinnacle3 treatment planning system and a Gaussian error function, respectively. As the parameters in the error function model (namely, a, b and c) were related to the shape of the cDVH curve, evaluation of cDVHs corresponding to the prostate motion based on the model parameters becomes possible, as demonstrated in this study. It was found that deviations of the cDVH for the CTV were significant, when the CTV‐planning target volume (PTV) margin was underestimated in the anterior‐posterior directions. This was especially evident in the posterior direction for a patient with relatively small prostate volume (39 cm3). Analysis of the cDVH for the CTV shifting in the anterior‐posterior directions using the error function model showed that parameters , which were related to the maximum relative volume of the cDVH, changed symmetrically when the prostate was shifted in the anterior and posterior directions. This change was more significant for the larger prostate. For parameters b related to the slope of the changed symmetrically from the isocenter, when the CTV was within the PTV. This was different from parameters c ( are related to the maximum dose of the cDVH), which did not vary significantly with the prostate motion in the anterior‐posterior directions and prostate volume. Using the patient data, this analysis validated the error function model, and further verified the clinical application of this mathematical model on treatment plan evaluations.

PACS number: 87.10.‐e, 87.55.‐x, 87.55.dk and 87.56.N‐
Accuracy of automatic couch corrections with on‐line volumetric imaging*
Authors: Li Winnie , Moseley Douglas J. , Manfredi Tony , Jaffray David A.
Published: November 2009

The purpose of this study was to characterize automatic remote couch adjustment and to assess the accuracy of automatic couch corrections following localization with cone‐beam CT (CBCT). Automatic couch movement was evaluated through passive reflector markers placed on a phantom, tracked with an optical tracking system (OTS). Repeated couch movements in the lateral, cranial/caudal, and vertical directions were monitored through the OTS to assess velocity and response time. In conjunction with CBCT, remote table movement for patient displacements following initial setup was available on four linear accelerators (Elekta Synergy). After the initial CBCT scan assessment, patients with isocenter displacements that exceeded clinical protocol tolerances were corrected using remote automatic couch movement. A verification CBCT scan was acquired after any remote movements. These verification CBCT datasets were assessed for the following time periods: one month post clinical installation, and six months later to monitor remote couch correction stability. Residual error analysis was evaluated using the verification scans. The mean ± standard deviations of couch movement based on phantom measurements with the OTS were in the L/R, A/P, and S/I couch directions, respectively. The fastest maximum velocity was observed in the inferior direction at 10.5 mm/s, and the slowest maximum velocity in the left direction at 3.6 mm/s. From 1134 verification CBCT registrations for 207 patients, the residual error for each translational direction from each month evaluated are reported. The μ was less than 0.3 mm in all directions, and σ was in the order of 1 mm. At a 3 mm threshold, 21 of the 1134 fractions (2%) exceeded tolerance, attributed to patient intrafraction movement. Remote automatic couch movement is reliable and effective for adjusting patient position with a precision of approximately 1 mm. Patient residual error observed in this study demonstrates that displacement is minimal after remote couch adjustment.

PACS number: 87.55.Qr, 87.56.bd, 87.57.Q
Prostate positioning errors associated with two automatic registration based image guidance strategies
Authors: Ryan D. , Rivest C. , Riauka Terence A. , Murtha Albert D. , Fallone B. Gino
Published: November 2009

Daily image guidance for helical tomotherapy prostate patients is based on the registration of pretreatment megavoltage CT (MVCT) images and the original planning CT. The goal of registration, whether manual or automatic, is the overlap of the prostate; otherwise prostate misplacement may compromise the efficacy of treatment or lead to increased toxicity. A previous study demonstrated that without the aid of implanted fiducials, manual registration results in inaccurate prostate positioning. The objective of this work is to quantify prostate misplacement that results from automatic bone matching (BM) and image matching (IM) registration algorithms. 204 MVCT images from eight high‐risk tomotherapy prostate patients were incorporated into this retrospective study. BM and IM registration algorithms – based on maximization of mutual information of bony anatomy only and the entire image, respectively – were used to independently register MVCT images to their respective planning images. A correlation coefficient based algorithm that uses known planning CT contour information was used for automatic prostate localization in each MVCT image. Daily prostate misplacement was determined by repositioning as calculated from the BM and the IM algorithms. Mean and maximum 3D prostate positioning errors were and 11.8 mm for bone matching, and and 11.5 mm for image matching. In terms of translational directions, IM would lead to prostate positioning error in any of the LR, AP or SI directions in 62% of treatment fractions. The corresponding value for BM is 51%. The values for positioning errors were 29% and 17% for IM and BM, respectively. This data suggests automatic daily image guidance for tomotherapy prostate patients should be based on bone matching instead of image matching.

PACS number: 87.19.xj, 87.57.nj
Planting trees for carbon credits: a discussion of context, issues, feasibility, and environmental benefits
Authors: Freedman Bill , Keith Todd
Published: November 2009

Increasing concentrations of certain atmospheric gases, particularly CO2, may be intensifying Earth's naturally occurring greenhouse effect. Anthropogenic emissions of CO2are mostly associated with fossil-fuel combustion and deforestation, both of which are intimately associated with diverse economically important activities. This circumstance will make it difficult for society to rapidly achieve large reductions in the emissions of CO2. The extensive planting of trees can contribute to offsetting a portion of the anthropogenic emissions of CO2and other radiatively active gases (RAGs). Growing plants fix atmospheric CO2into organic carbon of their accumulating biomass, and ecological budgets suggest that substantial carbon credits can be achieved by planting large numbers of trees, in both urban and rural environments. Moreover, many additional noncarbon environmental benefits are achieved by planting trees over extensive areas. A tree-planting strategy could not, however, be practically used to offset more than a relatively small portion of the RAGs emitted through human activities. This limitation is mostly due to the immense areas of land that would have to be afforested to achieve more substantial offsets. Ultimately, effectively dealing with an anthropogenic enhancement of Earth's greenhouse effect will require a comprehensive integrated strategy, the major component of which will be reduced emissions. However, carbon offsets associated with the planting of trees will also be an important element of that integrated strategy. This review discusses issues involved in the planting of trees to offset emissions of CO2and other RAGs. Forest-carbon offsets are discussed in the contexts of the greenhouse effect and climate change, options for reducing emissions of CO2, and the feasibility and environmental benefits of achieving CO2offsets by extensively planting trees. Attention is paid to both carbon and noncarbon benefits, in the contexts of industrial and nonindustrial forests, both urban and rural.Key words: forest-carbon offsets, carbon credits, afforestation, rural forest, urban forest.
Conceptualization of the acidification theory in Swedish environmental research
Authors: Ôberg Gunilla , Bäckstrand Karin
Published: November 2009

The aim of the present study was to describe and analyse the process of formulating the acidification theory in the Swedish research community. The empirical material was limited to articles written by Swedish researchers during the period 1950–1989 and published in international scientific journals utilizing a peer-review system. A model was developed to represent what Swedish researchers have regarded as the core of the acidification theory. Guided by the developed model, a qualitative content analysis of the scientific articles was conducted; i.e., we examined how central components and causal relationships of the theory have been explained and discussed. It should be emphasized that the present article describes an investigation of science itself (i.e., science in action) and is not an up-to-date review of acidification research. Our analysis revealed that some parts of the chain of evidence underlying the acidification theory were accepted before they were scrutinized by the scientific community and that the acidification complex was not conceptualized in accordance with the conceptualization of its various components. Actually, the acidification problem as a whole (i.e., the sum of all of its components) was not treated as a scientific theory that needed to be evaluated. This strongly indicates that the conceptualization was guided by factors that are generally, within the scientific community, considered to be external to the research process. There is no evidence that Swedish acidification research has adhered less stringently to scientific norms than environmental research in general has. Indeed, it is likely that such hidden patterns normally influence the conceptualization of science and we, therefore, conclude that the influence of factors that are not strictly a part of the research process must be further elucidated if the prerequisites and implications of research are to be clarified.Key words: scientific conceptualization, research process, acidification.
Two-phase sampling of woody and herbaceous plant communities using large-scale aerial photographs
Authors: Pitt D.G. , Glover G.R. , Jones R.H.
Published: November 2009

A two-phase sample design employing large-scale aerial photographs was used to quantify early successional woody and herbaceous plant community structures. Two conventional 35-mm cameras were mounted on a boom and suspended from a helium-filled blimp to obtain low-cost 1:366 scale stereo photographs (1:80 scale prints) of seven experimental vegetation complexes. Estimates of woody crown volume index and herbaceous percent cover were generated for 5 × 5 m plots by calibrating photo measurements to a limited ground-truth sample. The method offered significant increases in estimation precision (>35%) over ground sampling alone, as well as attractive cost advantages (0 to 40%). The highest levels of precision were obtained by measuring entire plots on the photographs. This procedure added approximately 10% to the cost of photo evaluations but resulted in estimates with standard errors that were, on average, 78% smaller than those of ground samples. Simulation trials suggested that more than nine ground-truth sample units per vegetation community type provided only marginal increases in estimation precision. If individual species or species groups of interest are well represented in sample areas, large-scale photographs, employed in a two-phase sample design, can be an effective tool for quantifying and monitoring vegetation community structures in silvicultural and related field studies.
Short-term influences on Canadian wood pulp prices and exports: a vector autoregression analysis
Authors: Alavalapati Janaki R.R. , Luckert Martin K. , Adamowicz Wiktor L.
Published: November 2009

The short-run dynamic impacts of macroeconomic variables on the Canadian pulp industry are investigated using the vector autoregression approach. The results show that shocks in the G10 exchange rate and the U.S. pulp price significantly affect Canadian pulp prices but not Canadian pulp exports. Short-term contracts, changes in the domestic demand for pulp, and limitations on pulp processing capacities are thought to be responsible for the limited responsiveness of pulp exports. The results also suggest that the indirect effect of shocks in the macroeconomy are important in explaining the dynamics of Canadian pulp price and pulp exports.
Dynamics of tree seedling populations in a humid subtropical forest of northeast India as related to disturbance
Authors: Bank S.K. , Rao P. , Tripathi R.S. , Pandey H.N.
Published: November 2009

Recruitment and survival of four important broad-leaved tree species, viz Quercusdealbata L., Quercusgriffithii Hk., Rhododendronarboreum Sm., and Schimakhasiana Dyer., were studied over 2 years in the undisturbed, mildly disturbed and highly disturbed forest stands of a subtropical humid forest of Meghalaya, northeast India. Recruitment of S. khasiana seedlings was maximum in the highly disturbed stand, while Q. dealbata seedlings were abundant in the undisturbed and mildly disturbed stands. Seedlings of Q. dealbata, Q. griffithii, and R. arboreum were equally successful in all the stands, while S. khasiana seedlings showed better survival in the highly disturbed stand than in the mildly disturbed and undisturbed stands. Six microenvironmental factors, viz photosynthetically active radiation, relative humidity, air temperature, soil temperature, soil moisture, and thickness of litter on the forest floor, were correlated with the age-specific mortality rate of seedlings. In Q. dealbata, Q. griffithii, and S. khasiana, mortality rate was significantly affected by microenvironmental factors, while in R. arboreum mortality was not correlated with any of the microenvironmental factors. On the basis of seedling recruitment and survival pattern, it was concluded that Q. dealbata, Q. griffithii, and R. arboreum were successful in both disturbed and undisturbed forest stands, while S. khasiana seedlings showed better survival and establishment in the disturbed stands.
Better derivations and an improvement for the specific increment equations of tree growth
Authors: Fleming Richard A.
Published: November 2009

Improved derivations are provided for the specific increments of internodal growth. These derivations strengthen the theoretical basis of the concept of specific growth. Despite being based on a more rigorous approach, however, these derivations produce a specific wood volume increment equation that is identical with the standard version. In contrast, a new equation emerges for the specific (annual) increment of cambial area: SAI = ln(rn/rn−1), where ln denotes the natural logarithm and rn and rn−1 are the cambial radii corresponding to the annual rings produced in years n and n − 1, respectively. The standard approximation underestimates the specific area increment, especially on young, fast-growing internodes, but even then the error involved may be small. Any standard approximation to SAI can be corrected by multiplication with the provided correction factor (which requires values for rn and rn−1 only).
Delayed impact of chronic ozone stress on young Douglas-fir grown under field conditions
Authors: Runeckles Victor C. , Wright Elaine F.
Published: November 2009

A 3-year study of the effects of low-level exposures of ozone (O3) on the growth of young Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) trees was undertaken during 1988–1990, using an open-air zonal air pollution system (ZAPS) on the University of British Columbia campus. The ZAPS provided daily O3 enrichment of the air during a 14-h daytime period starting at 07:00 Pacific daylight savings time, resulting in 12 unique exposure treatments, with additional control plots exposed to ambient air. Enrichment was provided for 92 days in 1988 and 101 days in 1989. The minimum and maximum 12-h (09:00–20:59 Pacific daylight savings time) seasonal mean O3 concentrations obtained were 18 and 41 ppb (nL/L) in 1988 and 27 and 66 ppb in 1989. Destructive harvests and nondestructive measurements were taken at intervals throughout the 1988 and 1989 exposure periods, and once in 1990. Variability within the tree population and the relatively low levels of exposure resulted in no significant effects on growth being observed until the latter part of the second year of treatment. In the later harvests in 1989, analysis by simple linear regression showed significant reductions in the dry weight of second-flush growth as a result of O3 treatment. The effect carried over into the third year, as revealed by small but significant reductions in leader length. In both cases, the use of nonlinear Weibull and gamma-type regression models resulted in improved fits to the data. Although young Douglas-fir trees are tolerant to modest increases in ambient O3 in the short term, extended periods of such exposures lead to adverse effects on long-term growth.
Foliar response of ozone-sensitive hardwood tree species from 1991 to 1993 in the Shenandoah national Park, Virginia
Authors: Hildebrand Elisabeth , Skelly John M. , Fredericksen Todd S.
Published: November 2009

During the late summers of 1991, 1992, and 1993, the occurrence and severity of foliar symptoms on ozone-sensitive eastern hardwood species (black cherry (Prunusserotina Ehrh.), yellow-poplar (Liriodendrontulipifera L.), and white ash (Fraxinusamericana L.)) in the Shenandoah National Park, Va., and relationships between the observed symptoms and cumulative ambient ozone exposures were determined. Three plots containing 30 trees of each species were established adjacent to air quality monitoring stations located at three different elevations. The symptom response of black cherry was most clearly correlated with ozone exposure. The best-fit regression model describing the relationship between cumulative ozone exposures and foliar injury was quadratic (y = a + bx2 + e); the most significant relationships were foliar injury versus the cumulative ozone concentrations of ≥60 ppb and the cumulative ozone concentrations weighted by a sigmoidal function. These observations suggest that higher ozone exposures are more important to foliar symptom development, but cumulatively all exposures contribute to the effect. In 1992, the progression of symptom development on 10 black cherry trees at each site was observed and related to cumulative ozone; there was an exponential increase of foliar injury with cumulative ozone throughout the summer. In 1993, eight subplots of five black cherry saplings were established, and ozone-induced symptom incidence and severity was compared with those on overstory trees at associated trend plots. There was no significant difference in symptom expression between overstory and sapling trees; therefore, Park Service personnel can use the more accessible saplings instead of overstory trees to monitor ozone symptoms in the Park.
AN EXTENDED BRACKET POLYNOMIAL FOR VIRTUAL KNOTS AND LINKS
Authors: KAUFFMAN LOUIS H.
Published: November 2009

This paper defines a new invariant of virtual knots and flat virtual knots. We study this invariant in two forms: the extended bracket invariant and the arrow polyomial. The extended bracket polynomial takes the form of a sum of virtual graphs with polynomial coefficients. The arrow polynomial is a polynomial with a finite number of variables for any given virtual knot or link. We show how the extended bracket polynomial can be used to detect non-classicality and to estimate virtual crossing number and genus for virtual knots and links.
MODELING USER-PERCEIVED RELIABILITY BASED ON USER BEHAVIOR GRAPHS
Authors: WANG DAZHI , TRIVEDI KISHOR S.
Published: November 2009

Service Reliability is an important consideration for new service deployment. Traditional system-oriented measures are no longer adequate to describe the reliability perceived by the user. In this paper we propose a general service reliability analysis approach based on user behavior, and derive formulas to compute service reliability from the user model and service models. The derived user-perceived service reliability incorporates the user task reliabilities, the dependencies of different user tasks, and various types of user behavior besides failure and recovery of system hardware and software components. This approach is applied to the service reliability computation for an example fault tolerant cluster hosing two services. Factors from both the system side and the user side are analyzed for the user-perceived service reliability of the cluster, and the results are compared with the system availability and service reliability lower bound.
THE BEST HEDGING STRATEGY IN THE PRESENCE OF TRANSACTION COSTS
Authors: ZAKAMOULINE VALERI
Published: November 2009

Considerable theoretical work has been devoted to the problem of option pricing and hedging with transaction costs. A variety of methods have been suggested and are currently being used for dynamic hedging of options in the presence of transaction costs. However, very little was done on the subject of an empirical comparison of different methods for option hedging with transaction costs. In a few existing studies the different methods are compared by studying their empirical performances in hedging only a plain-vanilla short call option. The reader is tempted to assume that the ranking of the different methods for hedging any kind of option remains the same as that for a vanilla call. The main goal of this paper is to show that the ranking of the alternative hedging strategies depends crucially on the type of the option position being hedged and the risk preferences of the hedger. In addition, we present and implement a simple optimization method that, in some cases, improves considerably the performance of some hedging strategies.
Effect of peripheral fused ring substitution on the optical spectroscopy and electronic structure of metal phthalocyanine complexes
Authors: Chidawanyika Wadzanai , Mack John , Shimizu Soji , Kobayashi Nagao , Nyokong Tebello
Published: November 2009

In this paper the impact of peripheral substitution with a strongly withdrawing fused ring group on the optical spectroscopy of a metal phthalocyanine complex is analyzed. We report the synthesis of [9 (or 10), 16 (or 17), 23 (or 24)-tri-tert-butylimidophthalocyaninato]zinc(II) (ZnttbIPc), which should eventually prove to be a useful precursor for forming dimeric compounds. The electronic structure is analyzed through a detailed analysis of the UV-visible absorption and magnetic circular dichroism spectra and time-dependent density functional theory calculations. Other than a marked splitting of the Q band, the spectrum is broadly similar to that of ZnPc in terms of the main π → π* electronic bands. The vibrational bands differ markedly in the Q band region when an imido group is added to ligand periphery, relative to what is observed in the case of zinc mononaphthotribenzotetraazaporphyrin ( Zn3B1N ) with an additional fused benzene ring. The absorption and emission spectra lack mirror symmetry as is the case with ZnPc and thus provide possible evidence for a second set of electronic origins in the Q band region arising from n → π* rather then π → π* transitions.