An Acoustics Operations Study for Loblolly Pine (Pinus taeda) Standing Saw Timber with Different Thinning History
There is currently a request from landowners in southeastern USA to provide a nondestructive tool that can differentiate the quality between stands of 25 and 30 years of age subjected to different thinning treatments. A typical site with various thinning regimes was used to vary the wood quality and to determine whether acoustics had the ability to separate for stiffness differences at a given age and local geography. A stand at age 29 with three different spacing (prior thinning) levels was chosen. Three hundred trees (100 per treatment) were randomly selected and acoustically tested for sound velocity using the Time-of-Flight (ToF) method for unthinned, thinned, and twice-thinned stands, respectively. The key finding of the study was that the estimated stiffness of the previously thinned treatments was actually greater than that of the unthinned group, despite having diameters as much as 28% larger. During a forest cruise, knowing that a higher-diameter stand is similar or higher in stiffness could raise the dollar value and harvest priority.
Distance error for determining the acoustic velocity of standing tree using tree morphological, physical and anatomical properties
Time-of-flight (ToF) acoustic tools is one of the most practical nondestructive methods for predicting tree stiffness. In the literature, 120 cm between probes has been adopted as the standard for the assessment of tree acoustic velocity. However, there is no empirical study supporting this assertion, hence this study is aimed at determining the effect of distance on error for a common ToF acoustic tool. Twenty-five trees each were randomly selected from four loblolly pine plantations. Seven distances from 120 to 10 cm between probes were used to measure velocity. The morphological characteristics, physical and anatomical properties of the selected trees were also determined. The results indicated, at distances below 60 cm, the waveform is dominated by the fundamental frequency of the transmitter probe hence the velocities determined within 10–60 cm are not statistically different. Consequently, distances from 80 to 120 cm constitute the optimum range for velocity determination for this ToF acoustic tool. Furthermore, velocity determined at 40 cm is significantly higher than that determined at 120 cm suggesting velocity is dependent on the between probes distance. Using 120 cm as a standard distance, the dynamic stiffness is overestimated by 13, 50, 102, and 197 MPa respectively for 100, 80, 60, and 40 cm. Finally, microfibril angle and the fiber wall thickness are the main anatomical properties driving the signal at the micro-level.
Inferring Learning Strategies from Students ’ Errors
Student models in an Intelligent Tutoring System (ITS) aim at representing both correct and incorrect knowledge of the student in a particular domain of learning. This data serves as the basis upon which the Tutor can dispense remedial feedback. This paper presents a framework in which learners’ errors are diagnosed, classified and linked to cognitive processes associated with learning. The cognitive processes we identify are those of generalization, misattribution and ignorance. Our system applies to the domain of Second Language Acquisition and our approach uses Chomsky’s linguistic theory of Principles and Parameters. We particularly concentrate on the acquisition of the Phrase Structure component.