Dimensional stability of MDF panels produced from fibres treated with maleated polypropylene wax     

Rosilei A. Garcia  Alain Cloutier  Bernard Riedl 《Wood Science and Technology》2005,39(8):630-650

Medium-density fibreboard (MDF) was produced from fibres treated with maleated polypropylene wax. The objectives of this study were to improve the dimensional stability of MDF panels by this treatment; to observe the maleated polypropylene wax distribution within the MDF panels using conventional fluorescence microscopy; and to determine the effects of the treatment on the mechanical properties and vertical density profile of the panels. MDF panels were produced from two resin types (urea-formaldehyde and melamine-urea-formaldehyde) and three maleated polypropylene wax contents (0, 3 and 5%). Photomicrographs show that maleated polypropylene wax forms agglomerates within the MDF panels which is an evidence of its poor distribution in our experimental conditions. Our results show an important reduction on thickness swelling and water absorption after water soaking for panels produced from treated fibres. Linear expansion and contraction in adsorption and desorption conditions between 80 and 50% relative humidity increased following fibre treatment. However, thickness swelling and shrinkage in similar conditions showed an important reduction following fibre treatment. The fibre treatment did not have negative effects on the mechanical properties or the vertical density profile of MDF panels. The modulus of rupture and modulus of elasticity in bending were increased by the treatment independently of maleated polypropylene wax content. The internal bond strength increased following the addition of 5% maleated polypropylene wax content.  相似文献   

Ray tracheids in Pinus radiata are more highly resistant to soft rot as compared to axial tracheids: relationship to lignin concentration     

Adya P. Singh  Uwe Schmitt  Ralf Möller  Bernard S.W. Dawson  Gerald Koch 《Wood Science and Technology》2006,40(1):16-25

A visual decay assessment of Pinus radiata wood, which was part of a framing timber in a house in the North Island of New Zealand, indicated the presence of surface decay. Microscopic observations, employing confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), provided evidence of decay by cavity-forming soft rot (SR) fungi. A comparison of ray tracheids (RT) with axial tracheids (AT) indicated that RT were considerably more resistant to SR than AT. In the heavily degraded regions of wood, where axial tracheid walls contained abundant SR cavities, the walls of RT contained only a few or no cavities. An assessment of lignin concentration in the cell walls by a combination of TEM, confocal fluorescence and UV microscopy provided evidence of greater lignin concentration in the secondary wall of RT as compared to AT, which may explain the observed greater resistance of RT to soft rot. Dedicated to Professor Dr. Dr. h.c. mult. Walter Liese on the occasion of his 80th birthday.  相似文献   

Influence of nurse birch and Scots pine seedlings on early aerial development of European beech seedlings in an open-field plantation of Central France     

Prevosto  Bernard; Balandier  Philippe 《Forestry》2007,80(3):253-264

Beech woodland can be restored by direct planting of beech (Fagussylvatica L.) seedlings in abandoned areas, but this methodis generally avoided in forestry because of the growth difficultiesof beech in full-light conditions. This study tested a methodthat consists of planting beech seedlings in full-light conditionswith silver birch (Betula pendula Roth.) or Scots pine (Pinussylvestris L.) as nurse trees. A total of 65 two-year-old beechseedlings surrounded by either 3, 4, 5 or 6 pine or birch seedlingsor without competitors were planted in bare-soil open-fieldconditions in Central France. Tree growth and light availabilitywere monitored at the end of each of the following 3 years,and soil moisture was also measured the last year. At the endof the experiment, aerial biomass measurements were made onthe beeches. Results showed that relative beech growth in termsof diameter was significantly reduced by the local neighbouringtrees and that this reduction was particularly noticeable inthe pine treatments where there was extensive pine seedlingdevelopment. In contrast, relative beech height did not exhibitany significant variations among the treatments. Light availabilitywas decreased by the neighbouring trees, especially in the pinetreatments. Light reduction was more pronounced in the last2 years and in the middle or lower parts of the canopy of thesubject beech. Soil water content was lower under the pine canopiesthan under the birch canopies, and was positively correlatedto beech relative diameter growth. Specific leaf area, height-to-diameterratio and crown length-to-crown width ratio weakly but significantlyincreased with competition from the neighbours. Beech biomasspartitioning was only weakly affected by the treatments. Thisstudy showed that nurse trees tend to reduce beech growth butimprove form although effects remained weak due to the insufficientlength of the experiment. Further studies are also needed toquantify the effects of the neighbourhood on the growth of competitiveherbaceous vegetation and on changes in the microclimatic conditions.  相似文献   

赤桉、尾叶桉接种外生菌根菌的效果分析     

仲崇禄  弓明钦  陈羽  王凤珍  关则冠  Neale Bougher  Bernard Dell 《广东林业科技》2001,17(2):15-19

在广东省阳西县开展赤桉和尾叶桉接种10个外生菌根菌的野外试验，根据造林后对树高、地径和胸径的观测，发现菌根菌与树种间存在互作效应，这种效应影响菌根菌接种效果；试验筛选出的菌株：H4461，适于尾叶桉，树高增加2％－21％，胸径增加13％－35％，对赤桉树高生长也有促进作用；H4339，对赤桉1年生内幼树树高生长有显著促进作用， 也改善径生长，也适用于尾叶桉；H4111，对赤桉、尾叶桉的后期生长有效果；E4100、H4331、H4338和H4317，有时对参试树种生长有改善作用；其它参试菌根菌E4070，H4937，H4314，在两树种间表现极不稳定。  相似文献   

Assessing forest soil CO(2) efflux: an in situ comparison of four techniques     

Janssens IA  Kowalski AS  Longdoz B  Ceulemans R 《Tree physiology》2000,20(1):23-32

A dynamic, closed-chamber infrared gas analysis (IRGA) system (DC-1: CIRAS-1, PP-Systems, Hitchin, U.K.) was compared with three other systems for measuring soil CO(2) efflux: the soda lime technique (SL), the eddy correlation technique (EC), and another dynamic, closed-chamber IRGA system (DC-2: LI-6250, Li-Cor, Inc., Lincoln, NE). Among the four systems, the DC-1 systematically gave the highest flux rates. Relative to DC-1, SL, EC and DC-2 underestimated fluxes by 10, 36 and 46%, respectively. These large and systematic differences highlight uncertainties in comparing fluxes from different sites obtained with different techniques. Although the three chamber methods gave different results, the results were well correlated. The SL technique underestimated soil CO(2) fluxes compared with the DC-1 system, but both methods agreed well when the SL data were corrected for the underestimation at higher fluxes, indicating that inter-site comparisons are possible if techniques are properly crosscalibrated. The EC was the only system that was not well correlated with DC-1. Under low light conditions, EC values were similar to DC-1 estimates, but under high light conditions the EC system seriously underestimated soil fluxes. This was probably because of interference by the photosynthetic activity of a moss layer. Although below-canopy EC fluxes are not necessarily well suited for measuring soil CO(2) efflux in natural forest ecosystems, they provide valuable information about understory gas exchange when used in tandem with soil chambers.  相似文献   

An ethicist's commentary on veterinarians and animal welfare          下载免费PDF全文

Rollin BE 《The Canadian veterinary journal. La revue veterinaire canadienne》2007,48(11):1114

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An ethicist's commentary on a farmer requesting antibiotics in the absence of his regular veterinarian          下载免费PDF全文

Rollin BE 《The Canadian veterinary journal. La revue veterinaire canadienne》2007,48(7):682

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An ethicist's commentary on increased cost of proper shipping          下载免费PDF全文

Rollin BE 《The Canadian veterinary journal. La revue veterinaire canadienne》2007,48(2):126

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Evaluation of an accelerometer for at-home monitoring of spontaneous activity in dogs     

Hansen BD  Lascelles BD  Keene BW  Adams AK  Thomson AE 《American journal of veterinary research》2007,68(5):468-475

OBJECTIVE:To determine the correlation between activity as measured by an accelerometer and videographic measurements of movement and mobility in healthy dogs. ANIMALS: 4 healthy dogs. PROCEDURES: After determination that accelerometers had good agreement, 5 identical accelerometers were used simultaneously to test their output at 8 locations (rotated among collar, vest, and forelimb stocking locations) on each dog. Movement and mobility for each dog were recorded continuously with a computerized videography system for 7-hour sessions on 4 consecutive days. Accelerometer values were combined into 439 fifteen-minute intervals and compared with 3 videographic measurements of movement and mobility (distance traveled, time spent walking > 20 cm/s, and time spent changing position by > 12% of 2-dimensional surface area during 1.5 seconds). RESULTS: 96% of values compared between the most discordant pair of accelerometers were within 2 SDs of the mean value from all 5 accelerometers. All mounting locations provided acceptable correlation with videographic measurements of movement and mobility, and the ventral portion of the collar was determined to be the most convenient location. CONCLUSIONS AND CLINICAL RELEVANCE: Use of an accelerometer was adequate for at-home activity monitoring, an important end point in clinical trials of treatment for chronic disease, and provided information about daily activity that is unattainable by other methods.  相似文献   

Biting midges overwintering in Belgium   总被引：6，自引：0，他引：6  

Losson B  Mignon B  Paternostre J  Madder M  De Deken R  De Deken G  Deblauwe I  Fassotte C  Cors R  Defrance T  Delécolle JC  Baldet T  Haubruge E  Frédéric F  Bortels J  Simonon G 《The Veterinary record》2007,160(13):451-452

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