Multivariate Calibration Using Covariance Adjustment

In this paper we treat linear calibration of multivariate chemical measurement instruments. Two new calibration methods for multicollinear spectral data are proposed. The methods are compared with established predictors on a set of data. The data consists of measurements of fat in fish meat and near infrared (NIR) reflectance measurements. The new methods give improvements compared with the established ones.     

Variance Calculations for Direct Adjusted Survival Curves,with Applications to Testing for No Treatment Effect

Several investigators have recently constructed survival curves adjusted for imbalances in prognostic factors by a method which we call direct adjustment. We present methods for calculating variances of these direct adjusted survival curves and their differences. Estimates of the adjusted curves, their variances, and the variances of their differences are compared for non-parametric (Kaplan-Meier), semi-parametric (Cox) and parametric (Weibull) models applied to censored exponential data. Semi-parametric proportional hazards models were nearly fully efficient for estimating differences in adjusted curves, but parametric estimates of individual adjusted curves may be substantially more precise. Standardized differences between direct adjusted survival curves may be used to test the null hypothesis of no treatment effect. This procedure may prove especially useful when the proportional hazards assumption is questionable.     

Bark beetle and woodborer responses to stand thinning and prescribed fire in northeastern US coastal and inland pitch pine barrens

1. Southern pine beetle, Dendroctonus frontalis, has expanded its range further into the northeastern United States. This expansion threatens rare and ecologically valuable interior and coastal pitch pine barrens.
2. Pitch pine barrens restoration and southern pine beetle infestation suppression often involve leaving downed dead wood that saproxylic insects can exploit.
3. Semiochemical-baited traps were used to investigate the response of bark beetles and woodborers to restoration treatments at Rocky Point State Forest and the Albany Pine Bush Preserve, examples of coastal and interior pitch pine forests, respectively.
4. A total of 29,598 saproxylic insects from 116 species of bark beetles and woodborers were captured at Rocky Point State Forest, while 23,117 individuals from 67 species were captured at Albany Pine Bush Preserve.
5. Ips spp. were abundant at both sites with 28%–47% and 42%–74% of total collections at Rocky Point State Forest and Albany Pine Bush Preserve, respectively.
6. Ips grandicollis did not respond to treatments at either site. However, Ips pini was found in higher numbers in thinned blocks in Rocky Point State Forest.

     

A technique to measure the components of root water potential using screen-caged thermocouple psychrometers

This paper describes a simple method which uses screen-caged thermocouple psychrometers to measure the water potential components of the roots of cotton (Gossypium hirsutum L.) grown in pots of sand or nutrient solution. Water stress was imposed by withholding irrigation from the sand-grown plants. Sampling was conducted inside a humidified chamber to prevent evaporative losses. The results obtained were within the range expected and comparable to the few published values for other plants. The technique enabled the demonstration of osmotic adjustment in cotton leaves and roots. Published with the approval of the Director of the Arkansas Agricultural Experiment Station.     

Solute adjustments in leaves of two species of wheat at two different stages of growth in response to salinity

Changes in leaf solute concentrations in response to salinity were measured at two growth stages in two species of wheat, Triticum turgidum L. cv. Aldura (Durum group) and Triticum aestivum L., cv. Probred that differed in their salt tolerances. Both species at 55 days of age were Na⁺-excluders, but the concentration of Na⁺ was 10 times higher in T. turgidum than T. aestivum at low to moderate levels of stress. The ratio then decreased until it was 2:1 at – 1.2 MPa. In T. turgidum, K⁺ concentrations decreased with increasing Na⁺ concentrations so that the sum of the two cations remained constant at all stress levels, but in T. aestivum K⁺ decreased more rapidly than Na⁺ increased. In both species growing in media at 0 to –0.6 MPa, the amounts of Mg²⁺ and Ca²⁺ in 55-day-old plants that could be extracted with hot water were below 0.1 mmol (g dry weight)^?1. Then, as osmotic potentials of media decreased further, hot water-extractable Ca²⁺ increased greatly until, at – 1.2 MPa, Ca²⁺ concentrations were almost equal to the sum of Na⁺ and K⁺. In the range of 0 to –1.0 MPa, the ratio of Cl^? to total cationic charge remained constant at 1:6 in T. aestivum and 1:2 in T. turgidum. However, at – 1.2 MPa, the ratio in both species had changed to 2:3. Sucrose and betaine concentrations were 4 and 48 μmol (g dry weight)^?1, respectively, in non-stressed plants of both species. At – 1.2 MPa, sucrose had increased 30-fold but betaine had increased only 2.5-fold. Proline increased exponentially relative to foliar Na⁺ in T. turgidum. In T. aestivum only plants grown at –1.2 MPa contained sufficient Na⁺ to stimulate the accumulation of proline. Although the quantities of the solutes in leaves of non-stressed 96-day-old plants differed from those in non-stressed younger plants, the patterns of change of organic solutes as the older plants were subjected to increasing saline stresses were the same as in younger plants with the exception of sucrose. Sucrose concentrations were much higher in leaves of non-stressed older plants and this sugar first increased and then decreased with decreasing osmotic potentials of media.