穿孔率对木质穿孔板吸声性能的影响

木质穿孔板具备良好的吸声特性,可用于控制噪声和优化室内声环境,且具有一定的强度和尺寸稳定性,已被广泛用做装饰材料。以中密度纤维板(MDF)为基材,利用阻抗管传递函数法测试穿孔率分别为0、3.14%、4.91%和7.07%的木质穿孔板吸声性能,测试时板后空腔为50 mm,分析穿孔率变化对木质穿孔板吸声特性各指标的影响规律,结果表明:随着穿孔率的增加,木质穿孔板的吸声系数峰值有所下降,吸声频带增宽,共振频率往高频方向移动。试验研究得出木质穿孔板的吸声规律与穿孔率的关系,为穿孔板的加工、应用及今后的进一步研究提供了一定的理论支撑。     

五种木质板材吸声性能的测量与分析

对市场上常见的5种木质板材吸声系数进行了检测。结果表明:木质穿孔板在低频段、木丝板在中频段、轻质纤维板和木纤维/聚酯纤维复合板在中高频段,分别显示了优良的吸声性能,而刨花板的吸声性能较差。     

仿生木材结构穿孔纤维板吸声性能

以中密度纤维板为基材,通过设计穿孔结构及打孔方式,达到拓宽木质穿孔板吸声频带和提高声学性能的目的.利用分层加工工艺制备了带侧孔结构的穿孔纤维板,采用阻抗管传递函数法对穿孔纤维板吸声性能进行了测试.通过正交试验方法,研究了主孔直径、穿孔率、倾斜角度对穿孔纤维板吸声性能的影响,并获得了较优的制备工艺,随后利用控制变量法研究...     

穿孔倾斜角度对3D打印仿生木材吸声结构的吸声性能影响

【目的】基于木材内部天然多孔构造设计仿生木材的复孔吸声结构,研究穿孔倾斜角度对3D打印仿生木材吸声结构的吸声性能影响,为开发仿生木材吸声材料奠定理论基础。【方法】利用Rhinoceros三维建模软件进行结构设计,采用3D打印技术制备出仿生木材吸声结构。对比3D打印穿孔板,基于阻抗管传递函数法探究穿孔不同倾斜角度(0°、15°、30°、45°、60°)对3D打印仿生木材吸声结构的共振频率和吸声系数的影响。【结果】1) 3D打印穿孔板有2个共振频率,分别位于中低频和中高频处;而3D打印仿生木材吸声结构有3个共振频率,分别位于中低频、中高频和高频处,木质穿孔板仅在中低频具有共振频率,二者差异显著。2)穿孔倾斜角度对3D打印穿孔板的吸声性能有一定影响,在中低频处,随穿孔倾斜角度增大,3D打印穿孔板的共振频率向低频方向移动,吸声系数峰值总体呈上升趋势,峰值均在0. 8以上,吸声性能较好;在中高频处,随穿孔倾斜角度变化,3D打印穿孔板的共振频率和吸声系数峰值均有所改变,但无明确规律,此段吸声系数峰值在0. 3左右,吸声性能较差。3)穿孔倾斜角度对3D打印仿生木材吸声结构的吸声性能有较大影响,中低频处与中高频处的吸声规律与3D打印穿孔板基本一致;在高频处,随穿孔倾斜角度增大,3D打印仿生木材吸声结构的共振频率向低频方向移动,吸声系数峰值均在0. 8以上,具有较好的吸声性能。【结论】穿孔倾斜角度的3D打印仿生木材吸声结构在中低频、中高频和高频处都有较好的吸声性能,在高频处,不同倾斜角度3D打印仿生木材吸声结构的共振频率跨度较大,可为以后全频率吸声结构的设计研究奠定理论基础。本研究结果为实现可设计吸声频率的新型复合材料提供一个新的研究方向,在一些特殊吸声环境领域具有较好的发展前景。     

两种多层复合木质吸声板的试验研究

针对木质吸声板低频段吸声系数低的问题,引入微穿孔中间层结构,制成孔+槽结构和变截面结构复合声学板;采用驻波管法按GBJ88-85<驻波管法吸声系数与声阻抗测量规范>对试件进行了吸声系数对比性试验,结果表明:在中间层引入微孔结构后,吸声板的吸声性能明显变好,低频范围的吸声系数显著提高.     

穿孔中密度纤维板的吸声性能

为了给穿孔中密度纤维板(MDF)的设计、加工及应用提供依据,采用阻抗管传递函数法,测试分析板厚、孔径、穿孔率和板后空腔深度对其吸声性能的影响。结果表明:穿孔MDF的吸声性能受板厚、孔径、穿孔率和板后空腔深度的共同影响,按优化工艺参数(板厚15mm,孔径3mm,穿孔率3.14%~4.91%,空腔深度50mm),穿孔MDF的吸声系数峰值可超过0.6。     

穿孔中密度纤维板的吸声性能北大核心

为了给穿孔中密度纤维板（MDF）的设计、加工及应用提供依据,采用阻抗管传递函数法,测试分析板厚、孔径、穿孔率和板后空腔深度对其吸声性能的影响。结果表明：穿孔MDF的吸声性能受板厚、孔径、穿孔率和板后空腔深度的共同影响,按优化工艺参数（板厚15mm,孔径3mm,穿孔率3.14%~4.91%,空腔深度50mm）,穿孔MDF的吸声系数峰值可超过0.6。     

桉木多层穿孔吸声板的制备及吸声性能评价

采用桉木多层胶合板制备穿孔吸声板,探讨孔径、穿孔率、胶合板厚度等因素对其吸声性能的影响。结果表明:穿孔率和胶合板厚度对试板吸声性能的影响极显著,孔径无显著性影响;制备穿孔吸声板较优工艺为:孔径3 mm、穿孔率14%、板厚18 mm;在声波频率100~6 300 Hz范围内,穿孔吸声板的平均吸声系数为0.5,在1 700 Hz附近,穿孔吸声板吸声性能最好。     

桉木多层复合穿孔吸声板工艺参数对甲醛释放量的影响

利用桉木胶合板制备木质穿孔吸声材料,采用40 L干燥器法测定板材甲醛释放量,通过全因子试验探讨单板层数、孔径、穿孔率等因素对穿孔板甲醛释放量的影响。结果表明:单板层数、穿孔率和孔径对桉木多层复合穿孔板甲醛释放量均有极显著影响,先后次序为单板层数穿孔率孔径;穿孔板的甲醛释放量随着单板层数和穿孔率的增加而增大,随着孔径的增大而降低,在满足桉木多层复合穿孔板吸声系数符合要求的情况下,可适当减少板材层数以降低甲醛释放量;甲醛释放量主要来源于穿孔板向外界释放的总面积,可采用对穿孔内壁进行封闭或使用无甲醛胶黏剂的手段,减少或避免吸声板因穿孔工艺带来的甲醛释放量增大。     

木塑复合材料吸声性能的研究现状

木塑复合材料作为一种新型材料,由于其独特的装饰性能已广泛应用于室内外装饰材料中,开发其声学方面性能是目前室内装饰材料的重要研究方向,具有广阔的发展前景。笔者结合多孔吸声机理与共振吸声机理特性,阐述了吸声材料在吸声结构设计及吸声性能增强等方面的研究进展,重点分析了木塑吸声材料的结构特性与吸声性能。通过归纳分析其他木质复合吸声材料研究成果,提出了在实际使用中改善与提高木塑复合材料吸声性能的几种方法(如发泡法、预留空腔法、蜂窝结构复合法、黏附装饰层法、叠加设计法等)。采用驻波管方法测试木塑吸音板在不同穿孔率与空腔深度的吸声系数,结果表明:在穿孔率为0%和3%的条件下,吸声系数随着空腔深度的增加先上升随后下降;在穿孔率为6%和9%的条件下,吸声系数随着空腔深度的增加而增加。通过以上方法,可以最大限度地增强木塑吸音材料的全频吸声性能,为木塑复合吸声材料在室内设计中的应用提供理论基础。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Natural Regeneration in Clear-cuts: Effects of Scarification,Slash Removal and Clear-cut Age

The effects of soil scarification (mounding), slash removal and clear-cut age on the natural regeneration in clear-cuts was evaluated using data from four sites in southern Sweden. The treatments were carried out during a good seed and establishment year for birch ( Betula pubescens Ehrh. and B. pendula Roth). Scarification had the strongest positive effect on the density of naturally regenerated seedlings, especially in birch, but also in pine ( Pinus sylvestris L.) and spruce [ Picea abies (L.) Karst]. Slash removal had a positive effect on birch density. No statistically significant effect of clear-cut age was found. In addition, no statistically significant interactions between clear-cut age and scarification or slash removal were found. The ingrowth of field vegetation was the fastest in areas that were not scarified, less rapid in areas scarified on old clear-cuts, and the slowest after scarification in fresh clear-cuts. In conclusion, it may be possible to control the density of birch during a good establishment year for birch. If birch is desired, the best combination of treatments is to remove the slash and scarify; otherwise, these treatments should be avoided.     

Risk Perception Among Non-industrial Private Forest Owners

Based on an enquiry, risk perception among non-industrial private forest owners is described in relation to climate change and forestry hazards. Of the respondents, 11% took action to remedy the effects of climate change. Out of a given set, hazards were ranked according to each respondent's experience of recent substantial financial loss to the estate and in relation to his or her willingness to make investments aimed at risk reduction. For each hazard, the respondent assessed the risk in four classes ranging from very high to negligible risk. Six hazards were considered most problematic in all three aspects: browsing damage, falling timber prices, damage by wind, spruce bark beetle, root rot and pine weevil. A majority of the respondents claimed to take action to reduce the risk associated with at least one hazard, while 35% did not know whether they did. Excluding climate change, the need for decision support was the largest in relation to damage by wind owing to a combination of perceived high risk and a high level of ignorance in relation to whether risk-reducing measures were taken.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Pasture production and tree growth in a young pine plantation fertilized with inorganic fertilizers and milk sewage in northwestern Spain

The use of organic waste materials such as milk sewage as an organic fertilizer could have the dual advantages of organic-waste disposal and reduced dependence on inorganic fertilizers. The effects of fertilization with (1) conventional mineral fertilization, (2) milk sewage sludge at 40 kg N ha⁻¹ target rate and (3) no fertilization on pasture production and tree growth were examined in an experiment consisting of two pasture mixtures under a one-year-old Pinus radiata plantation with a density of 2500 trees ha⁻¹. The two pasture mixtures were: (1) Dactylis glomerata L. var. saborto (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹); (2) Lolium perenne L. var. Tove (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹). The experiment began in the spring of 1995 using a randomized block design with three replicates in Castro Riberas de Lea (Lugo, Galicia, north-western Spain). Plot size was 12 × 8 m², with a 1 m buffer strip between plots. Two-year data showed that fertilization with either material had a positive effect on pasture production, with no significant difference between the two fertilization treatments. Tree growth in the milk sewage sludge plot was significantly higher than in the control plots. Inorganic fertilization increased pasture production, but affected tree growth negatively. The results show that milk sewage sludge could be used as a fertilizer in silvo-pastoral systems. This revised version was published online in June 2006 with corrections to the Cover Date.