Basic wood density is an excellent indicator of quality,it is correlated with numerous physical,physiological and mechanical characteristics of a species and is a good descriptor of wood quality and important indicato...Basic wood density is an excellent indicator of quality,it is correlated with numerous physical,physiological and mechanical characteristics of a species and is a good descriptor of wood quality and important indicator of tree performance in community ecology.An accurate method is thus needed to estimate wood density.The standard way is to calculate the ratio of the oven-dried mass of a wood sample divided by its green volume,but wood characteristics within and between growth rings are highly variable;the density can vary in the longitudinal and the radial directions.The present study investigates the longitudinal and radial fl uctuations in the basic density of Abies cephalonica Loud and Pinus halepensis Mill.Four logs were cut from four diff erent trees for each species and 16 discs were formed(two discs from each log,one at the base and one at the top).Each disc was cut into cubes where their distance from the pith was measured and then sorted into 2 cm wide concentric zones.The results revealed a mild decreasing trend in basic density from the foot of the trunk upward for both species.The pith in both species also seems to have a relatively high density,which in the immediate next growth rings decreases only to resume increasing toward the bark.展开更多
For Corylus avellana, pericarp permeability,seed desiccation tolerance, and the effect of warm and cold moist stratification combinations on germination and of outdoor sowing date on dormancy breaking and seedling eme...For Corylus avellana, pericarp permeability,seed desiccation tolerance, and the effect of warm and cold moist stratification combinations on germination and of outdoor sowing date on dormancy breaking and seedling emergence were investigated. Seeds with(intact fruit nut)and without the pericarp were subjected to an imbibition test, and water uptake was measured. After nuts had been stored for 5 months at 3–5℃, seeds and desiccated seeds were cold-stratified at 3–5 ℃(for 0, 1, 2 or 3 months),then tested for germination. Nuts were warm-stratified at 20–25℃(for 0, 1 or 2 months), then cold-stratified(for 0,1, 2 or 3 months) and tested for seed germination. The nuts were sown outdoors on three dates in the same year of their collection: 15 September(immediately after collection), 2 November, and 17 December, and emerged seedlings were counted the following spring. The pericarp was not a barrier to water uptake by the seed;however, the seeds imbibed water faster and had more mass when the pericarp was removed. Seeds tolerated desiccation;germinationpercentage was not reduced when seed moisture content was reduced to 8.71%. Germination of seeds without the pericarp(regardless of the moisture content) was the highest when the seeds were cold-stratified for 2 months.When seeds with the pericarp were tested for germination,2 months of warm stratification before a 2-month cold stratification maximized seed germination. For outdoor sowing of nuts, sowing date affected percentage of seedling emergence the following spring;early autumn sowing(immediately after collection) resulted in the best emergence.展开更多
In two-phase sampling, or double sampling, from a population with size N we take one, relatively large, sample size n. From this relatively large sample we take a small sub-sample size m, which usually costs more per ...In two-phase sampling, or double sampling, from a population with size N we take one, relatively large, sample size n. From this relatively large sample we take a small sub-sample size m, which usually costs more per sample unit than the first one. In double sampling with regression estimators, the sample of the first phase n is used for the estimation of the average of an auxiliary variable X, which should be strongly related to the main variable Y (which is estimated from the sub-sample m). Sampling optimization can be achieved by minimizing cost C with fixed var Y, or by finding a minimum var Y for fixed C. In this paper we optimize sampling with use of Lagrange multipliers, either by minimizing variance of Y and having predetermined cost, or by minimizing cost and having predetermined variance of Y.展开更多
文摘Basic wood density is an excellent indicator of quality,it is correlated with numerous physical,physiological and mechanical characteristics of a species and is a good descriptor of wood quality and important indicator of tree performance in community ecology.An accurate method is thus needed to estimate wood density.The standard way is to calculate the ratio of the oven-dried mass of a wood sample divided by its green volume,but wood characteristics within and between growth rings are highly variable;the density can vary in the longitudinal and the radial directions.The present study investigates the longitudinal and radial fl uctuations in the basic density of Abies cephalonica Loud and Pinus halepensis Mill.Four logs were cut from four diff erent trees for each species and 16 discs were formed(two discs from each log,one at the base and one at the top).Each disc was cut into cubes where their distance from the pith was measured and then sorted into 2 cm wide concentric zones.The results revealed a mild decreasing trend in basic density from the foot of the trunk upward for both species.The pith in both species also seems to have a relatively high density,which in the immediate next growth rings decreases only to resume increasing toward the bark.
基金supported by the research project from European Commission(EC-FP7-308313,ZEPHYR)。
文摘For Corylus avellana, pericarp permeability,seed desiccation tolerance, and the effect of warm and cold moist stratification combinations on germination and of outdoor sowing date on dormancy breaking and seedling emergence were investigated. Seeds with(intact fruit nut)and without the pericarp were subjected to an imbibition test, and water uptake was measured. After nuts had been stored for 5 months at 3–5℃, seeds and desiccated seeds were cold-stratified at 3–5 ℃(for 0, 1, 2 or 3 months),then tested for germination. Nuts were warm-stratified at 20–25℃(for 0, 1 or 2 months), then cold-stratified(for 0,1, 2 or 3 months) and tested for seed germination. The nuts were sown outdoors on three dates in the same year of their collection: 15 September(immediately after collection), 2 November, and 17 December, and emerged seedlings were counted the following spring. The pericarp was not a barrier to water uptake by the seed;however, the seeds imbibed water faster and had more mass when the pericarp was removed. Seeds tolerated desiccation;germinationpercentage was not reduced when seed moisture content was reduced to 8.71%. Germination of seeds without the pericarp(regardless of the moisture content) was the highest when the seeds were cold-stratified for 2 months.When seeds with the pericarp were tested for germination,2 months of warm stratification before a 2-month cold stratification maximized seed germination. For outdoor sowing of nuts, sowing date affected percentage of seedling emergence the following spring;early autumn sowing(immediately after collection) resulted in the best emergence.
文摘In two-phase sampling, or double sampling, from a population with size N we take one, relatively large, sample size n. From this relatively large sample we take a small sub-sample size m, which usually costs more per sample unit than the first one. In double sampling with regression estimators, the sample of the first phase n is used for the estimation of the average of an auxiliary variable X, which should be strongly related to the main variable Y (which is estimated from the sub-sample m). Sampling optimization can be achieved by minimizing cost C with fixed var Y, or by finding a minimum var Y for fixed C. In this paper we optimize sampling with use of Lagrange multipliers, either by minimizing variance of Y and having predetermined cost, or by minimizing cost and having predetermined variance of Y.
