Log Position Research Articles

Weather Bike: A Bicycle-Based Weather Station for Observing Local Temperature Variations

©2014 American Meteorological Society to a computer for analysis and plotting using Bluetooth wireless transfer, the small size (12.7 × 4.5 × 2.8 cm and 102 g), and the relatively low cost (~$350). The Kestrel 4000 was mounted on a Kestrel tripod clamp that was attached to the bicycle handlebar using a USA Gear bicycle handlebar camera mount. A Garmin Edge 800 GPS was also mounted on the bicycle to log position information during each ride. The time on the Kestrel 4000 was set to match the time on the GPS unit, allowing the Kestrel data to be easily georeferenced. The Kestrel observations were imported into Excel and plotted as a function of time. The decision to mount the Kestrel 4000 on a bicycle rather than making handheld measurements was based on the fact that the bicycle-mounted A nyone who has walked or bicycled from an open field into a forest on a warm, sunny day or into a shallow topographic depression in the early morning or evening has likely noticed an appreciable change in near-surface air temperature (hereafter referred to as temperature) across these land use and topographic types. (See the “For Further Reading” section for additional articles related to human biometeorology and the factors that influence how humans perceive changes in temperature.) These temperature changes occur on a small scale easily observed by a person moving under their own power. A handheld portable weather station (Kestrel 4000) capable of recording observations as frequently as every 2 s was mounted on a bicycle (Fig. 1) to observe local temperature variations in the vicinity of Boulder, Colorado, during the winter of 2013. The results presented here show examples of local temperature variability, with some changes in temperature in excess of 10°C over distances of the order of 1 km.

Partial Shrinkage and Proportion of Cracks in Juvenile and Adult Wood of Eucalyptus grandis W. Hill ex Maiden

Drying defects which modify the structure and dimensions of wood are extremely harmful, causing limitations of use. It is known that the anatomical structure of wood has direct influence on the drying quality, in which weaker tissues lead to higher incidence of defects. As the wood drying process advances, it leads to the removal of bound water and, consequently, to the shrinkage of cell walls, which makes wood shorten its dimensions, causing defects related to this phenomenon, such as end and surface checks. The aim of this work was to evaluate the difference in partial shrinkage and proportion of cracks in Eucalyptus grandis juvenile (with pith) and adult wood (without pith) during natural air drying. The proportion of cracks was measured according to Brazilian Standard NBR 9487: Grading of hardwood lumber, and the partial shrinkage was obtained by direct measurement method. There was not a statistically significant difference of partial shrinkage between juvenile and adult wood. Lumber from juvenile wood presented worse quality in natural air drying than adult wood. The influence of wood position (juvenile or adult) in log exerted higher influence on drying quality than shrinkage.

Veneer grades, recoveries, and values from 5-year-old eucalypt clones

Processing young, small eucalypt logs into veneer is a burgeoning industry across southern China. However, plantations supplying these logs were mostly established for pulpwood; little information is available on variation and selection among commercial eucalypt clones/varieties in regards to suitability for veneer production. Tree growth and log form were assessed on 11 eucalypt clones from a 5-year-old trial in southern China. Logs from these were rotary peeled for veneer; recovery percentages plus a range of quality and value traits were assessed on the outturn. Tree volumes, green veneer recovery ratios (%), veneer quality grades, log value, and value m−3 varied significantly among both clones and log positions up the stem. The clone with the best veneer recovery ratio (50.5 %) provided nearly twice that of the poorest clone (28.4 %). Average veneer value log−1 by clone ranged from RMB 6.7 (US$1) up to RMB 15.1 (US$2) and average value m−3 by clone ranged from 589 RMB m−3 (US$88) up to 925 RMB m−3 (US$139). Overall, sweep was the key factor influencing veneer recovery ratio and value. Knots, especially dead knots, holes and splitting were major factors influencing veneer quality grade. Middle and upper logs had significantly higher veneer recoveries, grades, and values m−3 than the lower logs. Excellent potential exists for selecting among eucalypt clones, and even among log positions within trees, for optimizing veneer production.

Controls on the rate of CO2 emission from woody debris in clearcut and coniferous forest environments

The rate at which CO2 is released from woody debris post-clearcut affects the long term carbon consequences of such disturbances. Changes in microclimate post-clearcut may alter the rate of woody debris decomposition from that in a mature forest. However, very few studies have explored post-disturbance rates of woody debris respiration and the possible influence of an altered microclimate, and even fewer have considered the role of log position in influencing rates of respiration. This study explored the effects of log position and microclimate variability on the rates of coarse woody debris (CWD) respiration. The rates of respiration of downed Norway spruce (Picea abies) logs were repeatedly measured in situ using an LI-6200 gas analyzer. Treatments included native logs in the clearcut site, native logs in a neighboring mature spruce stand, and logs transferred from the clearcut site to the mature spruce stand. The transfer logs showed the highest rates of respiration (0.44 ± 0.03 g CO2 m−2 log surface h−1), followed by the clearcut logs (0.36 ± 0.02 g CO2 m−2 log surface h−1), and spruce stand logs (0.30 ± 0.02 g CO2 m−2 log surface h−1) (P < 0.01). The boost in respiration found in the transfer treatment group was best explained by increases in log water content, while the slower rate of respiration in the spruce stand logs was best explained by the log’s contact/non-contact with the ground prior to the start of the observational campaign. CWD respiration was found to represent 18 ± 3 % of total daytime ecosystem respiration (R eco).

Effect of fertilization on cell size in wood of Eucalyptus grandis Hill ex Maiden

The use of fertilization in forest stands results in yield gains, yet little attention has been directed to its potential effects on the quality of wood produced. Information is scarce about the effect of fertilization on anatomical structures of older Eucalyptus wood. This work aims to study the effect of fertilization on tissue cell size of wood from a Eucalyptus grandis stand at age 21 years, the management system of which is based on selective thinning and fertilizer application at the start of the thinning season. Factors to consider include: presence or absence of fertilizers, two log positions and five radial (pith to bark) positions. Results led to the conclusion that fertilization significantly influenced only vessel frequency. Vessel element length was influenced by tree height. Fiber length, fiber diameter, fiber wall thickness, vessel element length, vessel diameter and vessel frequency were influenced by the radial position of the sample in relation to the log. A positive correlation was observed between fiber length, fiber diameter, fiber wall thickness, vessel element length, vessel diameter, ray width and radial position, while a negative correlation was observed between ray frequency and radial position.

3D porosity prediction from seismic inversion and neural networks

In this work, we address the problem of transforming seismic reflection data into an intrinsic rock property model. Specifically, we present an application of a methodology that allows interpreters to obtain effective porosity 3D maps from post-stack 3D seismic amplitude data, using measured density and sonic well log data as constraints. In this methodology, a 3D acoustic impedance model is calculated from seismic reflection amplitudes by applying an L 1-norm sparse-spike inversion algorithm in the time domain, followed by a recursive inversion performed in the frequency domain. A 3D low-frequency impedance model is estimated by kriging interpolation of impedance values calculated from well log data. This low-frequency model is added to the inversion result which otherwise provides only a relative numerical scale. To convert acoustic impedance into a single reservoir property, a feed-forward Neural Network (NN) is trained, validated and tested using gamma-ray and acoustic impedance values observed at the well log positions as input and effective porosity values as target. The trained NN is then applied for the whole reservoir volume in order to obtain a 3D effective porosity model. While the particular conclusions drawn from the results obtained in this work cannot be generalized, such results suggest that this workflow can be applied successfully as an aid in reservoir characterization, especially when there is a strong non-linear relationship between effective porosity and acoustic impedance.

Longitudinal growth strain as a log and wood quality predictor for plantation-grown Eucalyptus nitens sawlogs

Peripheral longitudinal growth strain (LGS) was measured on a total of 81, 22-year-old pruned Eucalyptus nitens trees from five thinning treatments in a plantation thinning trial in Tasmania. Growth strain data were gathered at breast height on each tree using the CIRAD-Foret method. The effects of thinning treatment and tree diameter on LGS and its relationships to solid-wood traits determined in a processing trial were examined. LGS was significantly higher in the direction of the prevailing wind and was not significantly affected by either thinning treatment or tree diameter. An index of log end splitting was positively related to tree diameter, sawlog position (upper/lower), and LGS, which explained up to an additional 20% of the variance after tree diameter and log position were accounted for in a linear regression model. High LGS and log end splitting were significant indicators of increased board end splitting.

Fourier series expansion in a non-orthogonal system of coordinates for the simulation of 3D alternating current borehole resistivity measurements

We describe a method to simulate 3D resistivity borehole measurements acquired with alternating current (AC) logging instruments. It combines the use of a Fourier series expansion in a non-orthogonal system of coordinates with an existing 2D goal-oriented higher-order self-adaptive hp-finite element (FE) algorithm. The method is used to simulate measurements acquired with both wireline and logging-while-drilling (LWD) borehole logging instruments in deviated wells. It enables a considerable reduction of the computational complexity with respect to available 3D simulators, since the number of Fourier modes (basis functions) needed to solve practical applications is limited (typically, below 13). The fast convergence of the method is studied via numerical experimentation by simulating two wireline and one LWD instruments in a deviated well across a possibly invaded formation. Numerical results confirm the efficiency and reliability of the method for simulating challenging 3D AC resistivity borehole problems in deviated wells, while avoiding the expensive construction of optimal 3D grids. We accurately simulate challenging electrodynamic problems within a few seconds (or minutes) of CPU time per logging position. The method is especially well-suited for inversion of triaxial electromagnetic (EM) measurements, since we demonstrate that the number of Fourier modes needed for the exact representation of the material function is limited to only one (the central mode) for the case of borehole measurements acquired in deviated wells.

A Parallel, Fourier Finite-Element Formulation with an Iterative Solver for the Simulation of 3D LWD Measurements Acquired in Deviated Wells

We describe a new method to simulate resistivity measurements acquired with induction logging instruments in deviated wells. The method combines: (1) a highly e-cient iterative solver, (2) a parallel implementation, (3) a Fourier Finite-Element (FFE) formulation in a non-orthogonal system of coordinates, and (4) a 2D hp-Finite Element (FE) goal-oriented self-adaptive grid-reflnement strategy. We apply the new method to simulate measurements acquired with a logging-while-drilling (LWD) instrument operating at 1.75MHz in a 55-degree deviated well. Numerical results conflrm the high-accuracy and e-ciency of the method. An error level below 1% is achieved in reservoirs with high-contrast in electrical resistivity using an average CPU time of 1{3 minutes per logging position.

Simulations of 3D DC borehole resistivity measurements with a goal-oriented hp finite-element method. Part II: through-casing resistivity instruments

We simulate direct current (DC) borehole resistivity measurements acquired in steel-cased deviated wells for the assessment of rock formation properties. The assumed data acquisition configuration considers one current (emitter) and three voltage (collector) electrodes that are utilized to measure the second difference of the electric potential along the well trajectory. We assume a homogeneous, 1.27-cm-thick steel casing with resistivity equal to 10 − 5 Ω· m. Simulations are performed with two different numerical methodologies. The first one is based on transferring two-dimensional (2D) axisymmetric optimal grids to a three-dimensional (3D) simulation software. The second one automatically produces optimal 3D grids yielded by a 3D self-adaptive goal-oriented algorithm. Both methodologies utilize high-order finite elements (FE) that are specially well-suited for problems with high-contrast coefficients and rapid spatial variations of the electric field, as it occurs in simulations that involve steel-cased wells. The method based on transferring 2D-optimal grids is efficient in terms of CPU time (few seconds per logging position). Unfortunately, it may produce inaccurate 3D simulations in deviated wells, even though the error remains below 1% for the axisymmetric (vertical) well. The method based on optimal 3D grids, although less efficient in terms of CPU time (few hours per logging position), produces more accurate results that are validated by a built-in a posteriori error estimator. This paper provides the first existing simulations of through-casing resistivity measurements in deviated wells. Simulated resistivity measurements indicate that, for a 30° deviated well, measurements in conductive layers 0.01 Ω· m) are similar to those obtained in vertical wells. However, in resistive layers (10,000 Ω· m), we observe 100% larger readings in the 30° deviated well. This difference becomes 3,000% for the case of a 60° deviated well. For this highly-deviated well, readings corresponding to the conductive formation layer are about 30% smaller in magnitude than those in a vertical well. Shoulder effects significantly vary in deviated wells.

Quaternary Stratigraphy in Northwestern Maine: A Progress Report

A preliminary Quaternary stratigraphy for northwestern Maine can be assembled from interpretation of ice-flow indicators (dispersal and erosional), exposed sections, and drill-hole logs. Evidence from the ice-flow indicators delineates at least four regions each with different ice-flow histories. The distribution of these regions may result from an eastward invasion of Laurentide source ice during the early portion of the late Wisconsinan and subsequent development of a local ice dome during the closing portion of the Late Wisconsinan substage. Exposed sections contribute the following probable sequence of events to the stratigraphy: 1) deposition of alluvial fans, 2) deposition of a gray compact till beneath eastward flowing (Laurentide) ice, 3) deposition of a brown till beneath northward flowing local ice, 4) deglaciation by a southward retreating ice margin. These events appear continuous and have all been provisionally assigned a Late Wisconsinan age. Drill-hole logs confirm the sequence derived from the exposed sections and allow extension of the Quaternary stratigraphy. The drill-log data show three associated groups of sediments that may in turn result from at least three separate ice margin advances and recessions. The uppermost group of sediments is correlated with those found in exposed sections. The position of the drill-hole logs in an over-deepened basin suggest erosion by at least one even earlier glaciation.

Higher log position is not associated with better physical fitness in professional soccer teams in South Africa

Objective. To assess the difference in physical fitness of players in successful versus less-successful professional soccer teams in South Africa. Design. Professional soccer players (N = 140) underwent a battery of tests assessing important physiological components during the early part of their competitive season. Players were then separated into two groups on the basis of their teams' final log position in the Premier Soccer League (PSL) in South Africa. Players in successful (N = 70) and less-successful (N = 70) teams were in the top four or bottom six positions on the log respectively. Descriptive statistics (mean ± standard deviation (SD)) were calculated for each group, and independent t-tests were used to compare the means of the groups for each of the physical tests. Main outcome measures. Body composition, flexibility, muscle strength-endurance, power, speed, agility, aerobic endurance, and repeat sprint distance. Results. There were no significant differences between groups for all measures of body composition, flexibility, repeat sprint distance, and agility. Significant differences (p &lt; 0.05) were found for sit-ups, aerobic endurance, and speed, but these were generally small, not meaningful differences in performance. Players in successful squads were significantly (p &lt; 0.01) older than those in less-successful teams. Conclusions. The results demonstrate that in South Africa level of physical fitness is not higher in more-successful compared with less-successful teams in the PSL. Factors other than physical fitness may be more important in determining successful league performance and discrimi-nate better between players in teams with different levels of success. Improving professional soccer performance may require coaches and trainers to focus more attention on technical and tactical skill development in sport-specific training once an acceptable standard of fitness has been attained.. South African Journal of Sports Medicine Vol. 19 (2) 2007: pp. 40-45

Impact of log position in the tree on mechanical and physical properties of black spruce medium-density fibreboard panels

Mechanical and physical properties of medium-density fibreboard (MDF) panels made from black spruce ( Picea mariana (Mill.) BSP) top, middle, and butt logs were studied. The analysis of variance and analysis of covariance were both performed to examine the impact of log position in the tree on panel modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), linear expansion (LE), thickness swell (TS), and water absorption. Results indicate that MOE and IB strength of MDF panels made from top and middle logs were significantly superior to those of panels made from butt logs; however, there was no significant difference in MOE and IB between panels made from top and middle logs. Water absorptions of top and middle log panels were significantly lower than that of panels made from butt logs, and the difference in water absorption between panels made from top and middle logs was not significant. TS of top log panels was the smallest among the panels from the three log positions in the tree and was significantly different from those of middle and butt log panels. TS of butt log panels was the highest, which was significantly different from that of top and middle log panels. The differences in LE among the panels made from top, middle, and butt logs were not significant. The comparison of MOR of top, middle, and butt log panels was dependent on panel density because of the interactions among the three groups. Top and middle log panels showed superior properties, because the thinner cell walls of fibres from top and middle logs resulted in an increased compaction ratio compared with the butt log panels. Panel density affected both panel MOR and MOE considerably; however, its impact on IB, LE, TS, and water absorption was not significant in this study. The equations describing the linear relationships between MOR, MOE, and panel density were developed.

Observational Asteroseismology of slowly pulsating B stars

We review the status of observational asteroseismology of slowly pulsating B (SPB) stars. Their asteroseismic potential is extremely good because the excited high-order g-modes probe the deep interior of these hot stars. To enable asteroseismic modelling, a sufficient amount of well-identified modes is mandatory. To reach this goal with ground-based observations, dedicated long-term and preferably multi-site campaigns are needed to increase the number and the accuracy of detectable frequencies. The first results for SPB stars based on observations obtained with the asteroseismic space-mission MOST are very promising, guaranteeing the success of missions like CoRoT, launched in December 2006. These results also indicate that high-precision observations are needed to detect and to study low-amplitude SPB stars. Although SPB pulsations are not restricted to slow rotators, there is some observational evidence for an amplitude drop towards high values of the projected rotational velocity. For several SPB stars, close frequency multiplets are observed. In some cases, the observed frequencies might be components of a rotationally split mode, but in other cases an alternative explanation is needed. Magnetic fields of a few hundred Gauss, that recently have been detected for fourteen confirmed members, can cause such frequency shifts. SPB stars can no longer be considered as non-magnetic stars and magnetic fields should be included in the theoretical models. We argue that mode identification of g modes still remains one of the main obstacles, although progress has been made in this field recently. Asteroseismic potential After conducting a systematic study of variability amongst B type stars, Waelkens (1991) introduced the slowly pulsating B (SPB) stars as an independent class of stars pulsating in high-order, low degree gravity modes (g modes) with typical periods of the order of days. These modes are excited by the opacity mechanism acting on the metal-bump. They are trapped deep in the interior of these hot stars, making them very interesting from an asteroseismic point of view. On the other hand, they are very difficult targets for in-depth asteroseismic studies because the theoretical frequency spectra of SPB stars are very dense, the observed amplitudes are low (cf. Fig. 4), and most of the currently known SPBs are multi-periodic, giving rise to beat periods of the order of months or even years. Currently, at least 51 confirmed and 65 candidate galactic SPB stars are known, of which 15 are in open clusters. Thanks to the OGLE-II and MACHO databases, extra-galactic SPBs were recently found: 59 in the LMC and 11 in the SMC (Ko laczkowski et al. 2006). For the SPB stars observed in the Geneva photometric system, the effective temperatures and surface gravities were determined with the code CALIB in the same way as described by De Cat et al. (2007). As shown in Fig. 1, these stars cover the (young) part of the theoretical SPB instability strip. This figure also illustrates the existence of a common part of the theoretical instability strip of the β Cep and SPB stars. At least 6 β Cep/SPB hybrids are currently known: 53Psc (LeContel et al. 2001), ιHer (Chapellier et al. 2000), ν Eri (Jerzykiewicz et al. 2005), HD 886 (Chapellier et al. 2006), HD13745, and HD19374 (De Cat et al. 2007). Since they simultaneously pulsate in low-order p/g modes and high-order g modes probing both the outer layers and the deep interior of these stars, they are ideal asteroseismic targets. 168 Observational Asteroseismology of slowly pulsating B stars Figure 1: Position in the (log(Teff ),log g)-diagram of the candidate (open symbols) and confirmed (full symbols) SPB stars for which Geneva photometry is available. The triangles indicate the hybrid β Cep/SPB stars. The stars with a detected magnetic field are given in black. The lower and upper dotted lines show the ZAMS and TAMS, respectively. The dashed lines denote evolution tracks for stars with M= 15, 12, 9, 6, and 3 M . The dash-dot-dot-dotted and dash-dotted lines represent the theoretical instability strips for β Cep and SPB modes provided by De Cat et al. (2007). A typical error bar is given in the lower left corner.

Molecular Mapping of Loci Affecting the Contents of Three Major Fatty Acids in Indian Mustard (Brassica juncea L)

The fatty acid constituents of mustard oil are palmitic, stearic, oleic, linoleic, linolenic and erucic acids. With the objective of mapping loci influencing the content of these fatty acids, a population of F6 generation recombinant inbred lines (RILs) derived from an inter-varietal cross of mustard was analyzed. Transgressive variation was evident for all the six fatty acids analysed irrespective of the levels of differences between the parents. The frequency distribution was normal for the linolenic acid, linoleic acid and stearic acid contents, while deviation from normality was observed for the other three fatty acids. The content of erucic acid was negatively correlated with the contents of all other fatty acids, which were positively correlated. Based on single marker analysis and interval mapping, two loci each for linoleic, linolenic and erucic acids were mapped to marker intervals on three linkage groups. Position of log of odds ratio (LOD) peaks suggested presence of common, linked and independently segregating loci for the fatty acid contents. The percentage of phenotypic variance explained by individual quantitative trait loci (QTLs) ranged from 10.5 to 19.5%, whereas the cumulative action of loci detected for different traits accounted for 16.3 to 27.6% of the variance. The additive effect for an individual locus ranged from 1.09 to 4.33. Presence of the favourable alleles at both the contributing loci in most of the RILs with a high linolenic acid content and of the unfavourable alleles in the lines with a low linolenic acid content indicated the possibility of pyramiding useful genes from phenotypically similar parental lines.

Log Grade Prediction for Standing Yellow-Poplar Trees in Eastern Kentucky

Abstract Information on the quality of logs in standing trees can aid resource managers and landowners in maximizing returns from timber harvests. However, little is published about the grade of logs in yellow-poplar (Liriodendron tulipifera) stands. In this study, discriminant analysis was used to develop classification functions to predict USDA Forest Service Log Grades for standing yellow-poplar trees in eastern Kentucky. The variables used to predict log grade are those commonly collected during forest inventory. This analysis indicates the importance of log position, merchantable height, and tree grade to log grade determination. The classification functions developed from the modeling data set correctly classified 80.9% of the log grades in a validation data set. These results provide a framework to resource managers and landowners for assessing yellow-poplar log quality in standing trees. South. J. Appl. For. 27(1):61–65.

The effects of pH on the interaction between capsaicin and the vanilloid receptor in rat dorsal root ganglia neurons.

1. The vanilloid receptor of sensory neurons is a polymodal nociceptor sensitive to capsaicin, protons, heat and anandamide. Although it is known that interaction occurs between these different mediators the mechanism by which this occurs is poorly understood. In this study capsaicin elicited currents were recorded from vanilloid receptors found in adult rat isolated dorsal root ganglia (DRG) neurons under conditions of varying pH and the mechanism whereby protons can modulate this capsaicin response investigated. 2. Under whole-cell voltage clamp, modulating extracellular pH shifted the position of the capsaicin log(concentration)-response curve. Acidification from pH 9.0 to pH 5.5 lowered the EC50 values from 1150+/-250 nM to 5+/-2 nM with coincident change in the mean apparent slope factor from 2.3+/-0.3 to 0.9+/-0.2 and no change in maximal response. 3. The magnitude of the potentiation seen on reducing extracellular pH was not significantly affected by changes in extracellular calcium and magnesium concentration. 4. The response to capsaicin was not potentiated by a reduction in intracellular pH suggesting a site of action more accessible from the extracellular than the intracellular side of the membrane. 5. Potentiation by low pH was voltage independent indicating a site of action outside the membrane electric field. 6. At the single channel level, reducing extracellular pH increased channel open probability but had no significant effect on single channel conductance or open time. 7. These results are consistent with a model in which, on reducing extracellular pH, the vanilloid receptor in rat DRG neurons, changes from a state with low affinity for capsaicin to one with high affinity, coincident with a loss of cooperativity. This effect, presumed to be proton mediated, appears to involve one or more sites with pK(a) value 7.4-7.9, outside the membrane electrical field on an extracellularly exposed region of the receptor protein.

Tracking African elephants with a global positioning system (GPS) radio collar.

Reviews December 1996 to May 1997 Global Postioning System (GPS) trials based on results from two bulls radio collared in Amboseli NP: M86 (38 years and in musth when collared) tracked for 134 days, and M169 (34 years) tracked for 168 days. The collars, containing the GPS instrument and VHF modem package on top with a battery pack at the bottom, were successful in obtaining fixes in 94.6% or 2,966 times out of 3,136 and 96.5% or 2,638 out of 2,734 attempts. Failure to log positions peaked just before dawn with a subsidiary low one hour after midday, these may be due to the animals lying down or being under shade trees. On average each elephant was located 20 times per day and downloadings conducted with a light aircraft every two weeks. Results were converted to speadsheets (MS Excel) from which maps were created using MapInfo software. Daily and hourly movements were plotted. Trials demonstrate GPS radio tracking of elephants is feasible and capable of generating high quality data 24 hours a day and under all weather conditions.

A theoretical and experimental approach to the active-to-passive transition in the oxidation of silicon carbide : Experiments at high temperatures and low total pressures

Active-to-passive oxidation transition in chemical vapour deposited β-SiC was investigated in the temperature range 1300≤T≤1700°C under low total pressures (100≤Ptot≤800 Pa) and relatively high linear gas flow rates (10≤Vgas≤60 m s1) by thermogravimetric analysis. For given T, Ptot and Vgas, the oxygen partial pressure at the transition, PtO2, corresponds to the value where the mass-loss rate per unit area of the oxidized sample, R, is maximum. Logarithms of PtO2 are linear functions of reciprocal temperature for given Ptot, and Vgas. Vgas has a significant influence on the position of the transition log(PtO2)–T-1 line. PtO2 is also slightly affected by an increase of Ptot from 100 Pa to 800 Pa. In passive oxidation at high temperatures (>1500°C), large bubbles form in the silica film which is then disrupted leading to a loss of material. In active oxidation, R significantly depends on Vgas: the kinetics is diffusion or mass transfer controlled under the conditions investigated in the present study. In both active and passive oxidation regimes, a mass loss of the test specimen is always observed; an explanation is proposed.

The measurement of grain orientations in an extruded electrode graphite using image analysis

A new image analysis method is described for determining the orientation of needle coke grains relative to the extrusion direction of a thermic electrode graphite, by measuring the orientation of volumetric shrinkage cracks lying parallel to the long axis of grains. The method is used to determine the orientation of grains as a function of radial position in a graphite log. The orientation of grains in the log with respect to the extrusion direction is greatest at the edge and decreases progressively towards the centre. This variation in grain orientation is attributed to effects of velocity gradients during the extrusion stage of manufacture.