bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Face Seals With Shrouded Pockets
Authors: Walowit Jed A. , Pinkus Oscar
Published: November 2009

The paper offers an analysis of face seals, using incompressible fluids, aimed at arriving at a quantitative basis for the design and optimization of seals. To improve its hydrodynamic and dynamic capabilities, the parallel face seal is provided with pockets pressurized by the sealed fluid, and shrouded at both the inner and outer peripheries. The relevant Poisson equation is solved for its hydrodynamic, hydrostatic, and squeeze-film components. A parametric study of various geometric permutations and operating conditions is then obtained from the computerized solutions. The results show that the contribution of the hydrostatic forces to stiffness is insignificant, and that both K3 and W3 can be ignored in the optimization of seal dimensions. For high seal pressures, the dominant force and leakage are geared to the hydrostatic component, whereas for low seal pressures, both the hydrodynamic and squeeze-film effects are important.
Dynamic Analysis of Noncontacting Face Seals
Authors: Etsion I.
Published: November 2009

The dynamic behavior of a noncontacting coned face seal is analyzed for the case of a rigidly mounted rotating seat and a flexibly mounted stationary ring taking into account various design parameters and operating conditions. The primary seal ring motion is expressed by a set of nonlinear equations for three degrees of freedom. These equations, which are solved numerically, allow identification of two dimensionless groups of parameters that affect the seal dynamic behavior. Stability maps for various seals are presented. These maps contain a stable-to-unstable transition region in which the ring wobbles at half the shaft frequency. The effect of various parameters on seal stability is discussed and an approximate expression for critical stability is offered. The theoretical model assumes frictionless flexible mounting of the seal ring such as in metal bellows. However, the results for critical stability can also be used as an upper limit for cases when friction in the secondary seal is present.
Dynamic Stiffness and Damping Characteristics of Compensated Hydrostatic Thrust Bearings
Authors: Ghosh M. K. , Majumdar B. C.
Published: November 2009

This paper deals with an analysis of the dynamic behavior of compensated hydrostatic circular step thrust bearings taking into account fluid inertia and recess volume fluid compressibility effects. The Reynolds equation for fluid film and the recess flow continuity equations are linearized using perturbation methods. Results in terms of dimensionless load capacity, oil flow rate, stiffness, and damping are presented for capillary and orifice compensated bearings. Results show a marked influence of fluid inertia and recess volume fluid compressibility on the performance of the bearing.
Characteristics of an Oil Squeeze Film
Authors: Parkins D. W. , Stanley W. T.
Published: November 2009

This paper presents both theoretically and experimentally determined characteristics of an oil squeeze film. In the experimental arrangement, an oil film was contained within two plane surfaces having only normal oscillatory relative motion. The effects of initial oil film thickness, peak to peak amplitude, and frequency of oscillation were measured. A finite difference treatment gave theoretical oil pressure fields and forces for any specified normal velocity. Comparisons were made between the pressure measured at one position and its theoretical counterpart over an oscillatory cycle. Subzero oil film pressures were measured. A steady state (in addition to the dynamic) oil film force was identified, whose magnitude and direction depend on the mean oil film thickness, oscillatory amplitude, and frequency. A region of unstable behavior was found. Theory agreed reasonably with practice, but over estimated some oil film pressures and gave time histories which exhibited phase differences with the measured counterpart. These differences were not explained by including the measured pad misalignment in the theoretical model. Further extensions to the theory are suggested.
The Morphology of Surface Damage Caused by Friction
Authors: Rozeanu L. , Pnueli D.
Published: November 2009

An effort is made to functionally connect the morphology of a surface damaged by friction with the sequence of events leading to the damage. The connection between a destructive situation and the resulting morphology is established. The reverse connection, i.e., the use of the morphology as a diagnostic tool, is not complete, mainly because some of the characteristics suggestive of the mechanisms are erased. Still, for cases of one friction pass, e.g., on a spiral track friction machine, the reverse connection is also established.
Single Pass Rub Phenomena—Analysis and Experiment
Authors: Kennedy F. E.
Published: November 2009

This paper describes an experimental and analytical investigation of the temperatures and deformations which occur during a single traverse of a steel blade tip over a flat, smooth, fully-dense copper surface. Experimental work was carried out on a pendulum-type test device, with forces, rub energy, surface temperature, and residual deformation being determined for each single-pass rub test. An analytical model was developed for studying the thermal and mechanical factors influencing surface temperature in these single-pass rubs. The analytical surface temperature predictions were verified by the experimental results.
Analysis of Externally Pressurized, Double-Pad, Gas Porous Thrust Bearing
Authors: Wu K. H. , Cusano C.
Published: November 2009

The load capacity and stiffness of double-pad circular and rectangular porous gas bearings are analytically studied. Design curves for load capacity and stiffness versus static bearing numbers, for different supply pressures and eccentricity ratios, are given. The load capacity and stiffness of both bearings reach a maximum value at some bearing numbers and then decrease. A comparison between the load capacity and stiffness of single and double-pad gas bearings is made.
An Experimental Investigation of Molecular Rarefaction Effects in Gas Lubricated Bearings at Ultra-Low Clearances
Authors: Hsia Y.-T. , Domoto G. A.
Published: November 2009

The experimental investigation discussed here gives experimental confirmation of the slip-flow theory for modeling hydrodynamic gas bearings with clearances below 0.25 microns. An interferometric technique employing two CW lasers is used to measure the small clearances with an accuracy of 0.025 microns. The effects of molecular rarefaction are studied by operating the slider bearing in different gas media of different mean free paths. Bearings operating at extremely high local Knudsen numbers are studied without approaching excessively high bearing numbers. Experimentally measured trailing edge clearances and pitch angles are compared with theoretical predictions using the modified Reynolds equation with velocity slip boundary conditions. Excellent agreement between experiment and theory is found for clearances as high as 1.60 microns to as low as 0.075 microns with corresponding ambient Knudsen numbers of 0.04 and 2.51, respectively.
Fretting Wear and Fretting Fatigue—How Are They Related?
Authors: Bill R. C.
Published: November 2009

Results from published literature and results obtained by the author are examined in detail to determine how fretting wear and fretting fatigue are related. The effects of various experimental parameters, including slip amplitude, number of fretting cycles, frequency of fretting motion, experimental atmosphere, temperature, and the performance of coatings and surface treatments, are surveyed. All of the results examined indicate that fretting wear and fretting fatigue are influenced in a consistent and analogous manner by controlled variations in experimental conditions. That is, conditions that tend to accelerate fretting wear also accelerate fretting fatigue failures. Correlation of the performance of coatings on material under fretting wear and fretting fatigue conditions is rather tenuous, partly because similar contact conditions for fretting fatigue and fretting wear are not available for very many materials.
Modification in Some Alloys by Sulfide Formation
Authors: Nakajima K. , Isogai A. , Imada Y.
Published: November 2009

Friction and wear properties of the Ni-M-S alloy system were examined by changing the composition of M (Mo, Nb or Fe) and S, respectively. Sulfides or complex sulfides such as MoSx or FeNbxSy formed during rubbing or annealing were found to be good materials as a friction modifier, and they were discussed relative to the transformation of non-stoichiometric into stoichiometric compound during abrading. The effect of adding Fe to the matrix was also investigated with the system, and it was found that the Fe especially improves the wear property, among others.
Effects of Bulk Thermal Properties on Polymer Transfer
Authors: El Sanabary A. F. , Play D. , Godet M.
Published: November 2009

Thickness of traces formed by rubbing soft polymers of predetermined viscoelastic properties against counterfaces of different thermal conductivities were measured. Results show that thickness is governed essentially by the variation of the mechanical properties of the polymer with temperature.
Development of Water Lubricated Bearing for Steam Turbine Application
Authors: Colsher R. , Anwar I. , Dunfee J. , Kandl M.
Published: November 2009

Compliantly mounted rigid pad bearings were designed and tested for steam turbine application. This turbine utilizes exhaust gas waste heat from the main marine gas turbine. Designing these bearings involves combining the fluid film characteristics with the compliancy of the elastic mounts. The present work examines both these aspects and presents design criteria for water lubricated journal bearing operating in laminar and turbulent flow regimes. The predicted bearing performance is checked by the test data.
Asymptotic Analysis of a Finite Gas Slider Bearing of Narrow Geometry
Authors: Shepherd J. J. , DiPrima R. C.
Published: November 2009

The method of matched asymptotic expansions is used to analyze the steady state pressure distribution and load bearing properties of a finite rectangular isothermal gas slider bearing when ε, the ratio of transverse to longitudinal dimensions of the bearing, is small and the bearing number Λ is moderate. General expressions for the pressure and load are obtained. Specific results are given for bearings with shallow crowning. The effects of the bearing number becoming large and the interaction between the two effects ε→0 and Λ→∞ are discussed.
The Influence of a Solid-Film Lubricant on the Action and Life of Metal Cutting Taps and Other Tools
Authors: Childs T. H. C. , Hartley D.
Published: November 2009

Three modes of tap failure have been considered: too high a cutting force, jamming of the swarf in worn corners of the cutting edges, and loss of thread form. In tests in which a high speed steel tap cut a 1.5 percent Ni-Cr-Mo steel with neat mineral oil as the lubricant, chip thickness and tap wear increased with tap use until the jamming limit was reached. Coating the tool with an inorganically-bonded molybdenum disulphide film did not alter the failure mode but increased tap life by reducing the rate of progress to failure. Adding an EP agent to the oil completely changed the route to failure and increased tap life even more. The tool coating reduced tapping forces only initially. It was soon mainly swept away. Thereafter, however, the residue still had an influence on tap performance through its action in reducing pick-up on the tap rake faces. Supplementary tests contrast the behavior of the coating in tapping and turning operations.
Ion Implanting Bearing Surfaces for Corrosion Resistance
Authors: Valori R. , Popgoshev D. , Hubler G. K.
Published: November 2009

A program is currently underway to use ion implantation to improve the tribological and corrosion characteristics of load bearing surfaces in both rolling element bearings and gears used in aircraft propulsion systems. This paper describes that aspect of the program concerned with the use of ion implantation for surface alloying of bearing components in order to alleviate the problem of corrosion in costly M50 steel mainshaft aircraft engine bearings. Results to data indicate that implantation of selected ion species can significantly improve resistance to both generalized and localized (pitting) corrosion without adversely affecting bearing performance or fatigue endurance life.
Displacements and Stresses in Dry Contacts Third Body and Conformity Effects
Authors: Kohen I. , Villechaise B. , Play D. , Godet M.
Published: November 2009

Narrow and wide contacts are simulated in this study by considering, respectively, a flat and a sector loaded against a circular disk. In turn, an artificial intermediate film simulates the interfacial film or third body commonly found in dry friction. Normal and tangential stress fields have been determined using a combined photoelastic and interferometric technique. Contact stress distributions are obtained under pure normal load or normal load and torque. Displacements are also calculated at contact from these fields using methods of complex potentials in plane elasticity. Results show that in the cases studied, from a theoretical solid mechanism point of view, the boundary conditions observed are satisfied by considering that there is no relative displacement over the contact zone which is common to two successive load steps.
Optimum Design of Metallic Reciprocating Seals
Authors: Etsion I.
Published: November 2009

A new concept for a reciprocating metallic seal which does not involve elastohydrodynamic effects is analyzed. Eccentricity is taken into account and optimization is performed to give maximum sealing capacity and low friction loss. Performance characteristics are presented and comparison is made between the optimum seal and conventional pumping rings. The comparison shows the advantage of using the new seal concept from the point of view of its high sealing capacity and low friction loss.
Preliminary Results on the Abradability of Porous, Sintered Seal Material
Authors: Wolak J. , Emery A. F. , Etemad S. , Choi S. R.
Published: November 2009

Preliminary results are presented for the case of titanium blade specimens, with bare tips (or covered with wear resistant, plasma sprayed materials) rubbing at 100 m/s against specimens of abradable nickel-chromium seal material moving toward the rotating blades at 0.0125 mm/s or at 0.025 mm/s. Using a two component dynamometer, the normal force of the rub interaction was measured and the shear component estimated. The elastoplastic properties of the seal material have been determined and those parameters as well as the rigidity of the rub tester system are considered in conjunction with those affecting the accuracy of the measurement of the forces arising at the blade-seal interface. The average and the “local instantaneous” temperatures of the seal specimen and the temperature of the blade tip surface during rubbing are presented as functions of time. A seal densification factor is defined and its functional relationships with contact force components, temperature, wear ratio and blade tip abrading capability are indicated.
Analysis of Gas-Lubricated Foil Journal Bearings
Authors: Heshmat H. , Walowit J. A. , Pinkus O.
Published: November 2009

This work is concerned with an evaluation of the performance of a gas journal bearing using a spring supported compliant foil as the bearing surface. The analysis, conducted for both single and multipad configurations, is concerned with the effects that the various structural, geometric, and operational variables have on bearing behavior. Following the solution of the relevant differential equation, tabular or graphical solutions are provided for a range of relevant geometric and operational parameters. The solutions include values of the colinear and cross-coupled spring coefficients due to both structural and hydrodynamic stiffness. Desirable design features with regard to start of bearing arc, selection of load angle, number of pads and degree of compliance are discussed.
Hyperthermal atomic hydrogen and oxygen etching of vertically oriented graphene sheets
Authors: Bagge-Hansen M. , Outlaw R. A. , Zhu M. Y. , Chen H. J. , Manos D. M.
Published: November 2009

Carbon nanosheets have previously been shown to be promising high current field emission cathodes for a variety of potential applications. The vertically oriented planar sp2 carbon nanosheets grown by rf plasma-enhanced chemical vapor deposition terminate with one to seven graphene sheets and grow to ∼1 μm in height. High current field emission, Je∼0.15 mA mm−2 (8 V μm−1), conducted within an ultrahigh vacuum system in a diode configuration in line-of-sight to a mass spectrometer, shows that CH4, CO2, and CO are generated as a result of cathode bombardment by hyperthermal oxygen and hydrogen neutrals and ions generated by electron stimulated desorption at the Cu anode. Confirmation of the mechanism was achieved by repeating the experiments using a Au anode. Simultaneous acquisition of I-V data and the partial pressures of reaction products in the mass spectrometer have shown repeatable, sustained CH4, CO2, and CO production. As these hyperthermal atomic hydrogen and oxygen species impinge on the sidewalls and edges of the carbon nanosheets, they bond to various sites throughout the sp2 carbon array. Progressively, as further hydrogen and oxygen arrive, CH4, CO2, and CO are formed and desorbed, thereby etching the film. Raman spectroscopy has confirmed a corresponding increase in defect sites (ID/IG increased from 0.57 to 0.81) over the test interval. Scanning electron microscopy cross sections of carbon nanosheet cathodes before and after high current lifetime testing (>200 h) show the average etching rate to be ∼1.7×10−3 nm/s.
Rapid fabrication of custom patient biopsy guides
Authors: Rajon Didier A. , Bova Frank J. , Chi Yueh‐Yun , Friedman William A.
Published: November 2009

Image‐guided surgery is currently performed using frame‐based as well as frameless approaches. In order to reduce the invasive nature of stereotactic guidance and the cost in both equipment and time required within the operating room, we investigated the use of rapid prototyping (RP) technology. In our approach, we fabricated custom patient‐specific face masks and guides that can be applied to the patient during stereotactic surgery. While the use of RP machines has previously been shown to be satisfactory from an accuracy standpoint, one of our design criteria – completing the entire build and introduction into the sterile field in less than two hours – was unobtainable.(1) Our primary problems were the fabrication time and the nonresistance of the built material to high‐temperature sterilization. In the current study, we have investigated the use of subtractive rapid prototyping (SRP) machines to perform the same quality of surgical guidance, while improving the fabrication time and allowing for choosing materials suitable for sterilization. Because SRP technology does not offer the same flexibility as RP in terms of prototype shape and complexity, our software program was adapted to provide new guide designs suitable for SRP fabrication. The biopsy guide was subdivided for a more efficient build with the parts being uniquely assembled to form the final guide. The accuracy of the assembly was then assessed using a modified Brown‐Roberts‐Wells phantom base by which the position of a biopsy needle introduced into the guide can be measured and compared with the actual planned target. These tests showed that: 1) SRP machines provide an average technical accuracy of 0.77 mm with a standard deviation of the mean of 0.07 mm, and 2) SRP allows for fabrication and sterilization within three‐and‐a‐half hours after diagnostic image acquisition. We are confident that technology is capable of reducing this time to less than one hour. Further tests are being conducted to determine the registration accuracy of the face mask on the patient's head under IRB‐approved trials. The accuracy of this new guidance technology will be verified by judging it against current frame‐based or frameless systems.

PACS number: 87.57.Gg
Detection of electron beam energy variations using a computed radiography system
Authors: Cai Yang C. , Ge Yuanyuan , Bernard Damian , Turian Julius , Chu James C. H.
Published: November 2009

A method to evaluate the electron beam energy constancy by employing the computed radiography (CR) system has been developed. In this method, a right triangular plastic wedge is used to produce a curve of the CR storage phosphor plate signal versus the wedge thickness. The curve, which resembles the percentage depth ionization curve of the clinical electron beams, can be used to derive the energy constancy metric . The sensitivity of the method was tested using polystyrene sheets of variable thicknesses. For electron energies up to 12 MeV, energy changes induced by 1.5 mm thick polystyrene can be detected, while a 2.3 mm thick polystyrene sheet is required for higher energies. The measurements were carried out over a two‐year period. The results showed a good reproducibility with the use of the same CR plate and cassette, and without the requirement of calibration procedures. The two‐year range of the was within the 99% confidence intervals, and the standard deviation of the was measured to be from 0.3 to 0.4 mm for different beam energies. This technique provides an efficient and accurate method to perform the electron beam energy check and could be used by centers equipped with the CR system without requiring additional detection devices.

PACS number: 87.56.Fc
4D‐PET data sorting into different number of phases: a NEMA IQ phantom study
Authors: Mancosu Pietro , Sghedoni Roberto , Bettinardi Valentino , Fioroni Federica , Aquilina Mark A. , Grassi Elisa , Fazio Ferruccio , Borasi Giovanni , Gilardi Maria C.
Published: November 2009

This study aims to evaluate the dependence of 4D‐PET data sorting on the number of phases in which the respiratory cycle can be divided. The issue is to find the best compromise to reduce the conflicting effects induced by increasing the number of phases: lesion motion on each set of images decreases, but on the other hand image noise increases. The IQ NEMA 2001 IEC body phantom was used to simulate the movement of neoplastic lesions in the thorax and abdomen, investigating the effect of: target size (10 37 mm), lesion‐to‐background activity concentration ratio (4:1 and 8:1), total acquisition time (3, 6, 12, 20 min), and number of phase partitions (1, 2, 4, 6, 8, 10, 13). The phantom was moved in a cranial‐caudal direction with an excursion of 25 mm and a period of 4.0 sec. Five parameters associated to lesion volume and activity concentration were considered to assess the capability of the 4D‐PET technique to “freeze” the phantom motion. The results for all the parameters showed the capability of the 4D‐PET acquisition technique to “freeze” the lesion motion. The division into six phases was found to be the best compromise between temporal resolution and image noise for the phase where the “lesions” move faster; whereas the partition into four phases could be used if a stable breathing phase is considered.

PACS number: 87.57.uk; 87.57.cp
Treatment planning of epithelial ovarian cancers using helical tomotherapy
Authors: Jamema Swamidas V , Mahantshetty Umesh , Goel Vineeta , Engineer Reena , Deshpande Deepak D , Sarin Rajiv , Shrivastava Shyam Kishore
Published: November 2009

Whole abdomen radiotherapy (WAR) for epithelial ovarian cancer, though effective, has been used sparingly due to inadequate target coverage and poor sparing of organs at risk (OAR) leading to significantly higher toxicities. Newer radiation techniques have shown potential for significant improvement in the therapeutic ratio. The purpose of this study was to evaluate helical tomotherapy (HT) for WAR. The objective parameters were to obtain uniform and adequate target coverage with maximum OAR sparing. HT plans were generated for five patients with field width of 5.0/2.5 cm, modulation factor of 3.5/3.0, and a pitch of 0.3. A dose of 25 Gy in 25 fractions was prescribed to the abdomen with a simultaneous boost of 45 Gy in 25 fractions to the pelvis. Dose‐volume parameters and various indices were analyzed and compared. Mean volume (standard deviation) of abdominal and pelvic PTV (planning target volume) was and , respectively. Mean length of PTV in cranio‐caudal direction was . Volume receiving 95% and 107% of the prescription dose (V95% and V107%) was and for abdominal‐PTV, and and 0% for pelvic‐PTV, respectively. Homogeneity and conformity indices were for abdominal PTV, and for pelvic‐PTV, respectively. Median dose received by the kidneys, liver and bone marrow was and , respectively. HT achieves an excellent coverage of WAR target with simultaneous pelvic boost and better organ (kidneys and liver) sparing. HT for WAR has the potential as consolidative therapy; this is being evaluated further in a phase II cohort study in epithelial ovarian cancers.

PACS number: 87.53 Kn, 87.55. D‐, 87.55.dk.
Effect of collimator and couch angle change on breast IMRT dose distributions
Authors: Yang Jie , Ma Charlie , Wang Lu , Chen Lili , Li Jinsheng
Published: November 2009

Intensity‐modulated tangential photon beams for breast cancer treatment can improve the dose uniformity significantly throughout the whole breast and reduce the dose to the lung and the heart when compared to the conventional technique. Before the first treatment, patient setup may require a change on the collimator angle and/or the couch angle based on the chest wall coverage according to the port films. The objective of this work is to investigate the effects of the collimator and the couch angle change on the dose distribution for breast cancer treatment using intensity‐modulated tangential photon beams, and to determine the clinical acceptable range of the angle change for routine treatment. Ten breast cases treated with intensity‐modulated tangential photon beams were analyzed in this study. Patient‐specific CT data and the radiation therapy planning (RTP) files obtained from our in‐house Monte Carlo based breast IMRT treatment planning system were used for IMRT dose recalculation with collimator or couch angle changes. The isodose distributions and DVHs were compared with the original plans, and the effects of the collimator and couch angle change to breast IMRT dose distributions were evaluated. Our results show that a 4° change in the collimator angle or the couch angle did not affect the dose distribution significantly and it is acceptable in the clinic for patient treatment.

PACS number: 87.10.Rt
Modeling the regeneration of oak stands in the Missouri Ozark Highlands
Authors: Dey Daniel C. , Johnson Paul S. , Garrett H.E.
Published: November 2009

This paper describes a method for modeling the regeneration of even-aged oak stands in the Ozark Highlands of southern Missouri. The approach is based on (i) a growth model that is applicable to both oak sprouts and advance reproduction and (ii) a method for probabilistically estimating future size distributions of trees. The modeling method is illustrated using sprouting frequency, survival, and 5th-year height data for stump sprouts of five oak species. To consider the large residual variation in estimates of future sprout heights, nonlinear regression estimates of heights and their prediction errors are simultaneously used to estimate the probability that a sprout originating from a parent tree of a given species and diameter will grow into a specified 5th-year height class. To account for sprouting and survival failures, those probabilities are multiplied by logistic regression estimates of the probability that a parent tree will produce a sprout that survives to age 5. The resulting joint probabilities facilitate predicting future height distributions of surviving sprouts when the model is applied to a preharvest inventory of overstory trees.
Determination of carbon fraction and nitrogen concentration in tree foliage by near infrared reflectances: a comparison of statistical methods
Authors: Bolster Katherine L. , Martin Mary E. , Aber John D.
Published: November 2009

Further evaluation of near infrared reflectance spectroscopy as a method for the determination of nitrogen, lignin, and cellulose concentrations in dry, ground, temperate forest woody foliage is presented. A comparison is made between two regression methods, stepwise multiple linear regression and partial least squares regression. The partial least squares method showed consistently lower standard error of calibration and higher R2 values with first and second difference equations. The first difference partial least squares regression equation resulted in standard errors of calibration of 0.106%, with an R2 of 0.97 for nitrogen, 1.613% with an R2 of 0.88 for lignin, and 2.103% with an R2 of 0.89 for cellulose. The four most highly correlated wavelengths in the near infrared region, and the chemical bonds represented, are shown for each constituent and both regression methods. Generalizability of both methods for prediction of protein, lignin, and cellulose concentrations on independent data sets is discussed. Prediction accuracy for independent data sets and species from other sites was increased using partial least squares regression, but was poor for sample sets containing tissue types or laboratory-measured concentration ranges beyond those of the calibration set.
Distribution spatiale de la régénération de l'épinette noire 8 ans après un feu en forêt boréale (Québec)
Authors: Filion Jacques , Morin Hubert
Published: November 2009

The spatial distribution of Piceamariana (Mill.) BSP seedlings was studied, 8 years after a forest fire, using a grid of adjacent quadrats in three populations of different densities. Microsite characteristics and relative position of nearby seed bearing trees were noted for each seedling. The density of the regeneration observed after the fire decreased with a decrease in the population density. The seedlings were mostly associated to concave microsites, colonized by sphagnum or polytrichum mosses, but not to burnt humus. They were found on organic matter with a thickness of 10 to 20 cm and presented a contagious spatial distribution associated to the presence of a seed bearing tree within a radius of approximately 2.5 m. Favourable microsites were not associated to the presence of seed bearing trees. The concentration of seedlings at the base of trees was primarily dependent on a short distance dispersal following a rapid and complete opening of the cones after the fire and, secondly, on the quality of the microsites.
Leaf and stem structure of poplar (Populus ×euramericana) as Influenced by O3, NO2, their combination, and different soil N supplies
Authors: Günthardt-Goerg M.S. , Schmutz P. , Matyssek R. , Bucher J.B.
Published: November 2009

Although increasing tropospheric ozone (O3) concentrations as well as precursor NO2 emissions and N deposition have been observed, the combination of their effects on deciduous trees is little understood. We therefore examined the growth and leaf injury response of a model tree (Populus ×euramericana (Dode) Guinier cuttings exposed before flush and until they reached a height of more than 1 m) to low and high soil N supply (105 or 315 mg N•L−1 substrate volume), to filtered air, and to filtered air with NO2 (sinusoidal daily course with a mean of 100 nL•L−1), with O3 (60 nL•L−1), or with a combination of both in climate-controlled chambers. High soil N increased total plant dry weight, leaf area, and xylem radius in plants fumigated with or without added NO2 or O3. The number of leaves increased with high soil N independent of added NO2. The stomatal density was influenced by soil N and by fumigations, but the appearance of leaf injury symptoms, leaf loss, specific leaf weight, and bark radius were not modified by the soil N regimes. NO2 alone, though applied in a sixfold ambient concentration, did not significantly increase plant growth. NO2 and O3 alone had opposite effects on specific leaf dry weight, stomatal density, and in the high fertilization regime, on the bark radius. The decrease in specific leaf dry weight and the appearance of early leaf symptoms were enhanced by NO2 added to O3. Visible leaf injury caused by O3 increased in parallel with microscopic changes in mesophyll cell walls, in the starch and protein patterns of mesophyll cells, in the bark cell content, and in the phloem sieve pores. NO2 enhanced the negative effect of O3 rather than compensated for a low soil N supply.
Calculating critical S and N loads and current exceedances for upland forests in southern Ontario, Canada
Authors: Arp Paul A. , Oja Tõnu , Marsh Marius
Published: November 2009

A steady-state mass-balance model was used to calculate critical loads of S and N deposition for maintaining acceptable long-term acidity levels within upland forests in southern Ontario. Preliminary estimates about critical S and N loads were obtained using existing information about soils, vegetation and atmospheric ion deposition from 12 forest sites, all located within provincial parks or conservation areas. The following were considered: wet atmospheric deposition of all major cations and anions; availability for plant uptake of N, Ca, Mg, and K in the rooting space of each soil; nutrient uptake and storage in the growing woody biomass of the forest stands; estimates of soil weathering; and mean annual air temperature, precipitation, and evapotranspiration. From this, regional isopleth maps were generated to depict the following: (1) current deposition patterns; (2) critical acidification loads and their current exceedances (or nonexceedances) for two acidification effects criteria for soil solutions, namely (i) acceptable Al concentrations ([Al]leach,crit) and (ii) acceptable Al to base cation concentration ratios ([Al]/[BC]leach,crit); (3) critical N-eutrophication loads and their current exceedances for acceptable levels of NO3-N concentrations in soil solutions ([NO3-N]leach,crit). It was found that the northern part of the study area (part of the Canadian Shield) is currently subjected to atmospheric S and N deposition in excess of critical loads, with [Al]leach,crit set at 0.02 mequiv./L or [Al]/[BC]leach,crirt set at 0.15 equiv./equiv. This sensitivity to acid precipitation is, as calculated, primarily due to shallow and weathering-resistant soils and soil parent materials (mostly granitic). The middle portion of the study area is calculated to receive N slightly in excess of the N eutrophication limit, when [NO3-N]leach,crit is set at 0.1 mequiv./L. Considerable co-deposition of base cations (Ca, Mg, K) in the middle and southern part of the study area alleviates some of the atmospheric acidification stress. This stress is further neutralized by the soils and bedrock of this region (predominantly calcareous).
SENSITIVITY OF THE BAYESIAN RELIABILITY ESTIMATES FOR THE MODIFIED GUMBEL FAILURE MODEL
Authors: MILADINOVIC BRANKO , TSOKOS CHRIS P.
Published: November 2009

The classical Gumbel probability distribution is modified in order to study the failure times of a given system. Bayesian estimates of the reliability function under five different parametric priors and the square error loss are studied. The Bayesian reliability estimate under the non-parametric kernel density prior is compared with those under the parametric priors and numerical computations are given to study their effectiveness.
IMPLIED AND REALIZED VOLATILITY IN THE CROSS-SECTION OF EQUITY OPTIONS
Authors: AMMANN MANUEL , SKOVMAND DAVID , VERHOFEN MICHAEL
Published: November 2009

Using a complete sample of US equity options, we analyze patterns of implied volatility in the cross-section of equity options with respect to stock characteristics. We find that high-beta stocks, small stocks, stocks with a low-market-to-book ratio, and non-momentum stocks trade at higher implied volatilities after controlling for historical volatility. We find evidence that implied volatility overestimates realized volatility for low-beta stocks, small caps, low-market-to-book stocks, and stocks with no momentum and vice versa. However, we cannot reject the null hypothesis that implied volatility is an unbiased predictor of realized volatility in the cross section.
OPTIMAL PORTFOLIOS WITH STOCHASTIC SHORT RATE: PITFALLS WHEN THE SHORT RATE IS NON-GAUSSIAN OR THE MARKET PRICE OF RISK IS UNBOUNDED
Authors: KRAFT HOLGER
Published: November 2009

The aim of this paper is to provide a survey of some of the problems occurring in portfolio problems with power utility, Non-Gaussian interest rates, and/or unbounded market price of risk. Using stochastic control theory, we solve several portfolio problems for different specifications of the short rate and the market price of risk. In particular, we consider a Gaussian model, the Cox-Ingersoll-Ross model, and squared Gaussian as well as lognormal specifications of the short rate. We find that even in a Gaussian framework the canonical candidate for the value function may not be finite if the market price of risk is unbounded. It is thus not straightforward to generalize results on continuous-time portfolio problems with power utility, Gaussian interest rates, and bounded market price of risk to situations where the short rate is Non-Gaussian or the market price of risk is unbounded.
SMALL-TIME ASYMPTOTICS FOR IMPLIED VOLATILITY UNDER THE HESTON MODEL
Authors: FORDE MARTIN , JACQUIER ANTOINE
Published: November 2009

We rigorize the work of Lewis (2007) and Durrleman (2005) on the small-time asymptotic behavior of the implied volatility under the Heston stochastic volatility model (Theorem 2.1). We apply the Gärtner-Ellis theorem from large deviations theory to the exponential affine closed-form expression for the moment generating function of the log forward price, to show that it satisfies a small-time large deviation principle. The rate function is computed as Fenchel-Legendre transform, and we show that this can actually be computed as a standard Legendre transform, which is a simple numerical root-finding exercise. We establish the corresponding result for implied volatility in Theorem 3.1, using well known bounds on the standard Normal distribution function. In Theorem 3.2 we compute the level, the slope and the curvature of the implied volatility in the small-maturity limit At-the-money, and the answer is consistent with that obtained by formal PDE methods by Lewis (2000) and probabilistic methods by Durrleman (2004).
Porphyrin-modified electrodes for solar energy conversion
Authors: Imahori Hiroshi , Umeyama Tomokazu
Published: November 2009

This mini review presents our recent developments in porphyrin-modified electrodes for solar energy conversion. Various porphyrins have been assembled on nanostructured semiconducting electrodes to achieve efficient photocurrent generation. First, porphyrins have been organized with fullerenes onto semiconducting electrodes to elucidate the relationship between the molecular structures, film structures, and photoelectrochemical properties of the modified electrodes. Formation of hole and electron-transporting highways in the porphyrin/fullerene composite film led to the remarkable enhancement of photocurrent generation. Second, porphyrin-modified single-walled carbon nanotubes have also been assembled onto semiconducting electrodes. The degree of chemical functionalization by the bulky porphyrins was found to have a large impact on the photoelectrochemical properties. Third, asymmetrically π-elongated porphyrins have been successfully employed in dye-sensitized solar cells to improve the cell performance as well as the light-harvesting properties. The power conversion efficiency of the fused porphyrin cell was improved by 50% compared to the reference cell using the corresponding unfused porphyrin. Finally, carboxyquinoxalino derivatives of zinc porphyrin have been further developed to extend the concept of asymmetrically π-elongated porphyrins. The maximum power conversion efficiency of 5.2% was obtained by using 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-6′-carboxyquinoxalino[2,3-b]porphyrinatozinc(II).
Transient states in photoinduced electron transfer reactions of porphyrin- and phthalocyanine-fullerene dyads
Authors: Lemmetyinen Helge , Tkachenko Nikolai , Efimov Alexander , Niemi Marja
Published: November 2009

This paper combines the most important results on studies performed by the authors during the last decade on photoinduced electron transfer reactions of pheophytin-, phthalocyanine-, and porphyrin-fullerene dyads, in which donor and acceptor moieties are covalently linked to each other. Practically all studied molecules form an intramolecular exciplex as a transient state before the formation of the charge separation state or tight ion pair. When the center-to-center distance of the donor and acceptor pair is short (7–10 Å) both the exciplex formation and primary electron transfer are extremely fast with rate constants of 7–23 × 1012 s -1 and 40–1400 × 109 s -1, respectively. Rates become slower when the distance and orientational fluctuation increases. No systematic correlation between free energies and the rates of the formation and recombination of the exciplex and the charge separation state, respectively, were observed. The mechanism is discussed in frames of the Marcus electron transfer and the radiationless quantum transition theories.
Merit-Based Scholarships and Student Effort
Authors: Hernández-Julián Rey
Published: November 2009

Twenty-one states offer merit scholarships that require students to maintain a minimum grade point average (GPA). Using a comprehensive administrative database from Clemson University, this study estimates the relationship between the incentives created by a South Carolina merit scholarship (LIFE) and students' academic performance. I hypothesize that being at risk of gaining or losing this scholarship will lead to increased effort and, as a consequence, higher grades. The results suggest that the incentives created by the scholarship increase GPAs by as much as 0.101 on a four-point scale, controlling for student and course characteristics. Moreover, the results indicate that for men the relationship between the risk of gaining or losing the scholarship and grades is large and statistically significant; for women, however, there is little evidence that the scholarship is related to grades.
On the Use of Problem-Specific Candidate Generators for the Hybrid Optimization of Multi-Objective Production Engineering Problems
Authors: Weinert K. , Zabel A. , Kersting P. , Michelitsch T. , Wagner T.
Published: November 2009

In the field of production engineering, various complex multi-objective problems are known. In this paper we focus on the design of mold temperature control systems, the reconstruction of digitized surfaces, and the optimization of NC paths for the five-axis milling process. For all these applications, efficient problem-specific algorithms exist that only consider a subset of the desirable objectives. In contrast, modern multi-objective evolutionary algorithms are able to cope with many conflicting objectives, but they require a long runtime due to their general applicability. Therefore, we propose hybrid algorithms for the three applications mentioned. In each case, the problem-specific algorithms are used to determine promising initial solutions for the multi-objective evolutionary approach, whose variation concepts are used to generate diversity in the objective space. We show that the combination of these techniques provides great benefits. Since the final solution is chosen by a decision maker based on this Pareto front approximation, appropriate visualizations of the high-dimensional solutions are presented.
Global Crisis
Authors: Joseph Mathew
Published: November 2009

The global economic crisis precipitated by the US financial collapse has spread to India first in the financial markets and has now started impacting the real economy. India was hit by the global crisis at a time when the economy was already slowing down and the crisis has brought the growth sharply down in the second half of 2008–09 and is forecast to bring it further down in 2009–10. The number of policy measures taken so far to combat the crisis will at best soften the blow but will not lead to a revival of the economy to a higher level of growth. The crisis has shattered business and consumer confidence, raised uncertainty and brought down investment and consumption demand. In this context, fiscal and monetary policies have a limited impact in stimulating the economy. Kick-starting the long-pending structural and regulatory reforms can help a strong economic recovery.
Impact of the effort–reward imbalance model on intent to leave among Belgian health care workers: A prospective study
Authors: Derycke H. , Vlerick P. , Burnay N. , Decleire C. , D'Hoore W. , Hasselhorn H.‐M. , Braeckman L.
Published: November 2009

The aim of this study was to analyse the impact of the effort–reward imbalance (ERI) model on intent to leave the current organization (ITL organization) and intent to leave the nursing profession (ITL profession) in a prospective way. A total of 1,531 health care workers who remained in their job filled in a self‐administered questionnaire at baseline and 1 year later. ERI was measured at baseline by a 23‐item questionnaire. Multivariate logistic regression analyses were performed. Within a population with low intent to leave at baseline, we found that an imbalance between high efforts and low rewards (extrinsic hypothesis) increased the risk of high ITL organization (OR 4.98; 95% CI 2.07–11.97) and high ITL profession (OR 1.84; 95% CI 1.03–3.30), 1 year later. A high level of overcommitment (OC; intrinsic hypothesis) was not predictive for both intent to leave outcome variables, neither was the interaction between high efforts/low rewards and a high level of OC (interaction hypothesis). Our results showed that a perceived effort‐reward imbalance (ERI) at work is a significant predictor of intent to leave among health care workers. This contribution concludes with some directions aimed at boosting nurses' retention and recommendations for future research.
Complexity of health care needs and interactions in multidisciplinary medical teams
Authors: Molleman Eric , Broekhuis Manda , Stoffels Renee , Jaspers Frans
Published: November 2009

By using an information processing and social identity approach, this study examines the relationships between the complexity of the health care needs of a patient and (1) the interactions among physicians during team meetings and (2) how the meeting participants evaluate the discussion. Three dimensions of the complexity of the health care needs are related to the interactive behaviour of medical specialists during meetings of multidisciplinary medical teams. Three medical teams from a Dutch university hospital, each discussing a total of 40 patients, were observed. The results show that component complexity was positively related to the amount of information team members exchanged, to positive reactions, and to the positive evaluation of the discussion. Two other dimensions (interrelatedness of needs and ambiguity) have to be considered in concert: interrelatedness was positively related to negative reactions but only if ambiguity was low; and, further, ambiguity was positively related to evaluative behaviour and to positive reactions, and negatively to the evaluation of the discussion, but only if interrelatedness was low.