不同x射线源测定木材微密度的研究

本文比较分析了三种x射线源(~(55)Fe、~(238)Pu和x光管)对木材进行微密度测定的精度,并对不同树种木材的质量衰减系数进行了测定和研究。     

A high-throughput X-ray-based method for measurements of relative wood density from unprepared increment cores from Picea abies

We have described a high-throughput method for ring width and relative wood density analysis of unprepared increment cores based on conventional computer tomography scanners (CT scanners) used in health care. The method was developed for analysis of 5-mm increment cores collected in forest genetic and tree breeding trials. For these studies, the relative differences between individuals are more important than the exact value. The method is highly efficient in terms of quantitative data collection from large number of samples. There are, however, limitations in terms of resolution and accuracy on very small volumes of wood that must be considered when using the method to measure individual growth rings or increment cores thinner than 5 mm. However, in studies comprising large number of samples, the use of cost-efficient CT scanning on the major part of the material, combined with more laborious high-resolution scanning on sub-samples can be a good combination for efficient determination of radial variation in growth rate and wood density.     

Applicability of effective medium theory to wood density measurements using terahertz time-domain spectroscopy

The use of an effective medium theory is important when accurately measuring wood density using millimeter and terahertz wave techniques. To confirm the applicability of this theory to the evaluation of wood density, the relative permittivity and dielectric loss of oven-dry flat-sawn specimens of 11 different wood species were measured in a frequency range of 0.15–1.2 THz using a transmission measurement system for terahertz time-domain spectroscopy. A mixture model based on the effective medium theory well explained the density dependence of relative permittivity over the entire frequency range, while it did not fully explain that of dielectric loss, especially for higher frequencies. This indicates that wood scatters the terahertz wave with a wavelength close to the transverse sectional dimensions of the pores in wood in the same way as Mie scattering. It was found from the dielectric loss spectrum of wood substance that the frequency around 0.23 THz was preferable for the nondestructive evaluation of wood.     

Measurements of fungal wood decay on Scots pine and beech by means of X-ray microdensitometry

In this work, we present a fast and promising method to evaluate the natural durability of wood based on X-ray microdensitometry. Tested on beech and Scots pine wood samples, our findings show that this methodology and the traditional EN standards methodology based on mass loss are strongly correlated. X-ray methodology is less time consuming (we can detect the effectiveness of the attack within 5–6 weeks) and less expensive (very cheap plastic Petri dishes instead of the expensive glass Kolle flasks); moreover, the proposed method allows to thoroughly examine the phases and the kinetics of the fungal attack, and to investigate the spatial repartition of the attack within the samples due to the low thickness of the sample.     

Detection of wood density by using a DOE sensor

HeNe laser light components scattered through small wood samples from Scots pine (Pinus sylvestris L.) were investigated using a diffractive optical element (DOE) sensor and the optical signals compared with optical density data extracted from x-ray negatives of the respective samples. Good agreement between the x-ray and optical signals was observed with respect to the gravimetric density of the Scots pine samples. Received 20 January 1999     

Early assessment of density features for 19 Eucalyptus species using X-ray microdensitometry in a perspective of potential biomass production

Eucalyptus plantations have been considered for bioenergy production and hence their biological characteristics that make them amenable to intensive short-rotation forestry. Wood density is an important parameter that directly affects fuel production. This study focuses on the early assessment of density features for 19 Eucalyptus species using X-ray microdensitometry in a perspective of potential biomass production. Average ring density, earlywood density, latewood density, latewood percentage and the heterogeneity index were studied. E. polyanthemos registered the highest mean wood density value (0.84 g cm^?3), and E. viminalis showed the lowest value (0.53 g cm^?3). An indicator for the potential wood biomass (PWB) was calculated, with E. maculata displaying the highest biomass production index (13.4 kg). Comparison of radial growth of these species showed appreciable differences. The PWB indicator points to the prospective good aptitude for short-rotation cycle for biomass production of E. maculata, E. botryoides, E. globulus, E. nitens and E. sideroxylon.     

培育措施对桉树木材性质的影响

桉树已成为华南地区最重要外来速生树种，合理高效的培育措施不仅需要提高单位面积木材产量，同时还要求生产出满足木材工业要求的优质原料。概述了国内外有关培育措施对桉树木材产量与材性影响的研究，为今后我国桉树木材生产部门与加工利用部门的密切合作，提供参考。     

EFFECT OF TIMBER DENSITY ON RETENTION OF WOOD PRESERVATIVES

The amount of CCA fixed in the southern pine treated with CCA have been eval-uated.The conclusions from these experiments are:with the timber density increases,the reten-tion based on weight/weight will decrease,but the retention based on weight/volume will bealmost constant.Retention by weight would be more influential than by volume.     

The accuracy of medical CAT-scan images for non-destructive density measurements in small volume elements within solid wood

Summary A comparison between identically sampled CAT-scan images of five wooden test pieces (Pinus sylvestris) showed that the CT-number in each pixel varied with a standard deviation of ±3.9–11.1 CT numbers. This inaccuracy in CT-numbers is called noise. As long as the direction of rotation can be controlled the noise in CAT-scan images of wood can be assumed to be approx. ±4 CT-numbers in each pixel. A calculation showed the average CT-number must differ ±1 unit to distinguish average CT-numbers in 2 × 2 × 1.5 mm volumes within solid wood. It has previously been shown that a change of ±1 CT-number corresponds approx. to a change in density of ±1 kg/m³. On the other hand, there is a difference in X-ray absorption coefficients between wood and water. Thereby dry wood densities in corresponding volumes must differ approx. ±2 kg/m³ to significantly be distinguished. The corresponding figure is approx. ±6 kg/m³ for wet wood densities with moisture content levels ranging from 6–100%.     

Evaluation of intra-ring wood density profiles using NIRS: comparison with the X-ray method

Key message

Pith-to-bark wood density profiling is interesting in forestry science. By comparing it with the X-ray method, this study proved that a fiber optic NIR spectrometer with a high-precision displacement system could accurately measure intra-ring wood density with a spatial resolution of 0.5 mm.

Context

Most near-infrared spectroscopy (NIRS) studies for wood density determination use samples that have been pulverized beforehand. Attenuation of ionizing radiation is still the standard method to determine wood density with high spatial resolution. However, there is evidence that NIRS could be an accurate and affordable method for determining intra-ring density in solid wood strips.

Aims

In this study, we research whether the results published for intra-ring density predictions in wood can be improved when calibrated with X-ray microdensitometry.

Methods

The measurements were made using a fiber optic probe with a separation between measurement points of 0.508 mm in a range between 1200 and 2200 nm. A total of 4520 density points were used to create partial least squares regression (PLSR). X-ray densitometry data were used as reference values. Twenty PLSR calibrations were randomly executed on 31 samples collected from 28 Pinus radiata D. Don trees.

Results

Upon selecting 20 latent variables, the R ² value was 0.873 for the training group and 0.895 for the validation group, while RMSEP values are 43.1 × 10^?3 and 47.1 × 10^?3 g cm^?3 for the training and validation groups, respectively. The range error ratio (RER) was 13.7.

Conclusion

The RER was high and almost in the range suggested for quantification purposes. Results are superior to wood density studies in the literature which do not employ spatial resolution and to those found in studies using hyperspectral imaging.

     

Effect of growth conditions on wood density of Spanish Pinus nigra

The natural forests of Laricio Pine (Pinus nigra Subsp. salzmannii) cover in Spain an area of 353,000 ha, producing annually 310,000 m³ of roundwood. This species is considered as the fourth, most important Spanish conifer, being its timber frequently used in construction. The natural area of distribution of Laricio pine in Spain is officially divided into ten different regions of provenance, being only four of them considered as productive. The present study on the influence of growth conditions on extracted wood basic density (EBD) is carried out on 89 P. nigra trees, sampled from the two most productive Spanish regions of provenance (R.7 and R.8) in seven different sites. Cross-sectional disks were cut at 3 m (in 89 trees) and every 3 m height (in 18 trees) from the butt up to 15 m. For assessing the pattern of radial variation of the properties, 20×20×20 mm³ wood samples were taken radially from every cross-sectional disk. In every 20×20×20 mm³ wood sample, age and distance to the pith of the central annual ring was recorded, together with the average growth rate. Extractive content and EBD were measured in every sample. The results lead to the conclusion that there is not a significant relationship between EBD and provenance or growth rate. On the contrary, a significant relationship has been found between EBD and site quality or cambial age. The results also demonstrate that in a tree EBD tends to diminish from the base to the top and from the pith outwards. The main result of the present study is related with the observation that for the same cambial age, annual ring width has no significant influence on EBD, confirming that its utility as a predictor of the quality of timber is highly questionable, at least if the ring curvature is not considered.     

Temperature effects on wood anatomy, wood density, photosynthesis and biomass partitioning of Eucalyptus grandis seedlings

Wood density, a gross measure of wood mass relative to wood volume, is important in our understanding of stem volume growth, carbon sequestration and leaf water supply. Disproportionate changes in the ratio of wood mass to volume may occur at the level of the whole stem or the individual cell. In general, there is a positive relationship between temperature and wood density of eucalypts, although this relationship has broken down in recent years with wood density decreasing as global temperatures have risen. To determine the anatomical causes of the effects of temperature on wood density, Eucalyptus grandis W. Hill ex Maiden seedlings were grown in controlled-environment cabinets at constant temperatures from 10 to 35 degrees C. The 20% increase in wood density of E. grandis seedlings grown at the higher temperatures was variously related to a 40% reduction in lumen area of xylem vessels, a 10% reduction in the lumen area of fiber cells and a 10% increase in fiber cell wall thickness. The changes in cell wall characteristics could be considered analogous to changes in carbon supply. Lumen area of fiber cells declined because of reduced fiber cell expansion and increased fiber cell wall thickening. Fiber cell wall thickness was positively related to canopy CO2 assimilation rate (Ac), which increased 26-fold because of a 24-fold increase in leaf area and a doubling in leaf CO2 assimilation rate from minima at 10 and 35 degrees C to maxima at 25 and 30 degrees C. Increased Ac increased seedling volume, biomass and wood density; but increased wood density was also related to a shift in partitioning of seedling biomass from roots to stems as temperature increased.     

Combined effect of wood moisture content,drill bit rotational speed and feed rate on drilling resistance measurements in Norway spruce (Picea abies (L.) Karst.)

ABSTRACT

An IML-RESI PD 400 drilling tool and a standard spade drill bit (IML System GmbH, Wiesloch, Germany) were used to study the combined effect of wood moisture content (MC), drill bit rotational speed and feed rate on drilling resistance (DR) and feeding force (FF). Tests were made with Norway spruce (Picea abies (L.) Karst.) conditioned in a normal climate (20°C/65% RH), at 20°C/95% RH, vacuum-pressure impregnated in water, and oven-dried. Rotational speeds and feed rates had an impact on feed rate per cutting edge for the major cutting edge of the drill bit which was used for correlation with DR and FF for various MC. Impact of MC on DR and FF depended on rotational speeds and feed rates of the drill bit. For feed rates per cutting edge less than 0.09?mm, DR was higher for water saturated (WS) specimens. Negligible differences between DR for various MC were found for feed rates per cutting edge between 0.09 and 0.15?mm. DR was higher at low MC for feed rates per cutting edge which were higher than 0.15?mm. FF extremely increased in conditioned (20°C/95% RH) and WS specimens at feed rates per cutting edge less than 0.1?mm.     

Douglas-fir wood quality studies part I: Effects of age and stimulated growth on wood density and anatomy

Douglas-fir trees about 21 years old and growing on a poor site were thinned and fertilized causing accelerated growth. The characteristics of the wood across the 30-year age span were studied for 7 trees from the treated plot. Four trees of nearly uniform ring growth were also studied for some characteristics. Radial and tangential tracheid diameters, tracheid length and percent latewood were correlated quite well with log of age, coefficients ranged from 0.76 to 0.88 on pooled data. All tracheid dimensions when correlated with log of age gave high coefficients on a within-tree basis. The strongest relationship in all age-related factors was between 0 and 12 to 14 years. Specific gravity increased with age in all trees to about 16 to 18 years, then leveled off.Fertilization and thinning caused immediate production of lower density wood with somewhat lower percent latewood, a slight decrease in tracheid diameter tangentially but slightly greater radially, and a small decrease in tracheid length. The effects were mainly in the first 3 to 4 years after treatment, then there was recovery to normal wood density and cell dimensions. Wood from the trees of uniform growth showed no significant change over the same time period in percent latewood, specific gravity, and tracheid length.The research was financed by funds from State of Washington Initiative 171, Institute of Forest Products and the College of Forest Resources, University of Washington, Seattle.     

Effects of carbonization temperatures on microstructure of carbon fiber precursors prepared from liquefied wood

In order to enlarge the utilization field of wood and decrease the costs of carbon fibers, carbon fiber precursors from liquefied wood were prepared by soaking liquefied wood in a solution containing hydrochloric acid and formaldehyde, after melt-spinning by adding hexamethylenetetramine. The microstructure evolution of the precursor during carbonization was studied by FTIR, X-ray analysis and Raman spectroscopy. The results show that precursors from liquefied wood above 400°C had diffraction peaks corresponding to the (100) crystal plane. When the carbonization temperature reached 500°C, Raman spectroscopy showed the D peak at wave number of 1360 cm–1 and the G peak at 1595 cm–1. By increasing the carbonization temperature, the microstructure of the precursors became more ordered. Although the structure of the precursor changed at 500 and 800°C, the peaks at 1632 and 1454 cm–1 corresponding to the characteristic vibrations of aromatic rings, remained during carbonization. This implies that the precursor from liquefied wood cannot be easily formed into graphite.     

不同林分密度对桉树幼林木材材性的影响

对两种桉树无性系(巨细桉DH201-2和尾巨桉DH32-29)在5种不同林分密度下(1250、1657、2500、5000和6667株.hm-2)的木材材性(包括木材基本密度和纤维形态特征)进行了测量和研究分析(纤维形态特征分两种不同材型分析:心材与边材)。结果表明:无性系DH201-2的林分密度3(2 500株.hm-2)木材基本密度最大,为452 kg.m-3,DH32-29以林分密度2(1657株.hm-2)的木材密度最大,为436 kg.m-3;相同无性系相同林分密度下,边材纤维长度比心材纤维长度长,边材长宽比一般比心材长宽比要大,纤维宽度则无显著差异;无性系DH201-2的林分密度3(2500株.hm-2)和林分密度5(6667株.hm-2)是符合林分蓄积量、木材基本密度和纤维长度最大值的组合。     

乔木柳无性系木材基本朱内变异的研究

利用乔木柳12年生无性系对比试验林的材料，研究了13个柳树无性系木材基本密度株内径向和纵向的变异模式，并对密度选择的时期和取样位置进行了探讨。结果表明：（1）在1.3m高度，乔木柳无性系各年轮组木材戏向变异多数为“M”型曲线，即从木芯向外第、至第3年轮组（1－6a）的木材密度逐渐增加，第4年轮组（7－8a）略有下降，第5年轮组（9－10a）又有明显增加，至最外侧年轮（11－12a）木材密度则显著下降，根据各无性系的变异特点，分成3种类型，其中无性系221的变异较为独特，为典型的“N”型；（2）乔木柳无性系生长期密度变化的规律为：1－2年生时木材基本密度相对较低，3－4a以后密度相对稳定并接近无性系加权平均密度，3－4年生时木材基本密度与5－12年生时的测定值相关系数为0.789－0.985，均达到极显著相关水平（α＝0.01），5－12年生乔木柳无性系木材基本密度的变异为62.2％－97.0％与3－4年生时木材基本密度的值有关，3－4a作为5百木柳木材基本密度的选择年龄最为合适；（3）供试群体木材密度株内纵向变异模式大多也可用“M”型曲线加以描述，具典型的苴孔材绷向密度变异特征，根据各无性系的变异特点，分成4种变异类型；树干高1.3，3.6和7.2m处的木材基本密度与无性系平均密度的相关系数达到显著和极显著水平，可以在树干1.3m处取样以推测无性系平均值；（4）在供试群体中，有的无性系木材基本密度纵向和径向变异的幅度均很小，木材较为均一，如苏柳791，表明在乔木柳杂种后代中选择木材均一的柳树新品种是可能的。