Testing for variation in the western Oregon softwood log price structure

2005 ◽  
Vol 35 (3) ◽  
pp. 713-723 ◽  
Author(s):  
Ståle Størdal ◽  
Darius M Adams
Keyword(s):  
Douglas Fir ◽  
Reduced Form ◽  
Exogenous Variables ◽  
Varying Coefficients ◽  
Wage Rates ◽  
Time Patterns ◽  
Production Technologies ◽  
Flexible Least Squares ◽  
Time Varying Coefficients ◽  
Log Price

Timber owners in western Oregon have been concerned about the erosion of price premiums for higher quality grades of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) sawlogs over the past decade. Time series tests indicate that the ratio of 3Saw (lower quality) to 2Saw (higher quality) sawlog prices did rise over the 1990–2000 period, suggesting convergence between the prices. To identify causes of this trend, we estimate reduced form equations for Douglas-fir sawlog prices with time-varying coefficients using flexible least squares. Log grade prices were related to prices of lumber by grade, prices of chipped residues, labor wage rates, and volumes of public timber supplied. Changes in the relation of log grade prices are reflected through changes in both reduced form coefficients and levels of the exogenous variables. Changes in the coefficients, in turn, may derive from shifts in the distribution of log qualities within grade categories and from grade-specific changes in sawing and log production technologies. Coefficient trends showed that higher quality lumber grades became more important for 3Saw logs during the sample period, while lower quality lumber grades and chips became more important for 2Saw, moving the log grade prices closer together. Comparison of simulated 2Saw and 3Saw prices with and without historical time patterns in the exogenous variables had little impact on their relationship, suggesting that factors shifting the coefficients may have been the primary drivers of price convergence.

scholarly journals Measuring the Effect of Government Response on COVID-19 Pandemic: Empirical Evidence from Japan

COVID ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 276-287
Author(s):  
Rui Wang
Keyword(s):  
Least Squares Method ◽  
Empirical Finding ◽  
Japanese Government ◽  
Time Varying ◽  
Multiple Series ◽  
Government Response ◽  
Varying Coefficients ◽  
Flexible Least Squares ◽  
The Government ◽  
Time Varying Coefficients

The basic approach of this research is to use an estimated series of effective reproduction number Rt and multiple series of index from Oxford COVID-19 Government Response Tracker (OxCGRT) to measure the effect of Japanese government’s response on COVID-19 epidemic by running a time-varying regression with flexible least squares method. Then, we use estimated series of time-varying coefficients obtained from the previous step as proxy variables for the government response’s effect and run stepwise regressions with policy indicators of OxCGRT to identify which specific policy can mitigate the spreading of the COVID-19 epidemic in Japan. The main finding is that the response of Japanese government on COVID-19 epidemic is basically effective. However, the effect of Japanese government’ policy is gradually weakening. Under our identification scheme, we find that policies of quarantine and movement restrictions are still most effective, but policies of public health system do not show much effectiveness in the regression analysis. Another important empirical finding is that policies of economic support are effective in reducing the spread of COVID-19. Within the framework of empirical strategy proposed in this paper, the conclusion should be explained in the context of the socio-political and health situation in Japan, but the methodology is assumed to be applicable to other countries and regions in the analysis of government performance of response to COVID-19.

scholarly journals The VIT Transform Approach to Discrete-Time Signals and Linear Time-Varying Systems

Eng ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 99-125
Author(s):  
Edward W. Kamen
Keyword(s):  
Discrete Time ◽  
Initial Conditions ◽  
Linear Time ◽  
Order Term ◽  
Initial Time ◽  
Time Varying ◽  
Varying Coefficients ◽  
Time Signals ◽  
Time Varying Systems ◽  
Time Varying Coefficients

A transform approach based on a variable initial time (VIT) formulation is developed for discrete-time signals and linear time-varying discrete-time systems or digital filters. The VIT transform is a formal power series in z−1, which converts functions given by linear time-varying difference equations into left polynomial fractions with variable coefficients, and with initial conditions incorporated into the framework. It is shown that the transform satisfies a number of properties that are analogous to those of the ordinary z-transform, and that it is possible to do scaling of z−i by time functions, which results in left-fraction forms for the transform of a large class of functions including sinusoids with general time-varying amplitudes and frequencies. Using the extended right Euclidean algorithm in a skew polynomial ring with time-varying coefficients, it is shown that a sum of left polynomial fractions can be written as a single fraction, which results in linear time-varying recursions for the inverse transform of the combined fraction. The extraction of a first-order term from a given polynomial fraction is carried out in terms of the evaluation of zi at time functions. In the application to linear time-varying systems, it is proved that the VIT transform of the system output is equal to the product of the VIT transform of the input and the VIT transform of the unit-pulse response function. For systems given by a time-varying moving average or an autoregressive model, the transform framework is used to determine the steady-state output response resulting from various signal inputs such as the step and cosine functions.

scholarly journals Estimating latent group structure in time-varying coefficient panel data models

2019 ◽  
Author(s):  
Jia Chen
Keyword(s):  
Panel Data ◽  
Data Models ◽  
Panel Data Models ◽  
Time Varying ◽  
Clustering Method ◽  
Varying Coefficient ◽  
Varying Coefficients ◽  
Time Varying Coefficients ◽  
Latent Group ◽  
Group Structures

Summary This paper studies the estimation of latent group structures in heterogeneous time-varying coefficient panel data models. While allowing the coefficient functions to vary over cross-sections provides a good way to model cross-sectional heterogeneity, it reduces the degree of freedom and leads to poor estimation accuracy when the time-series length is short. On the other hand, in a lot of empirical studies, it is not uncommon to find that heterogeneous coefficients exhibit group structures where coefficients belonging to the same group are similar or identical. This paper aims to provide an easy and straightforward approach for estimating the underlying latent groups. This approach is based on the hierarchical agglomerative clustering (HAC) of kernel estimates of the heterogeneous time-varying coefficients when the number of groups is known. We establish the consistency of this clustering method and also propose a generalised information criterion for estimating the number of groups when it is unknown. Simulation studies are carried out to examine the finite-sample properties of the proposed clustering method as well as the post-clustering estimation of the group-specific time-varying coefficients. The simulation results show that our methods give comparable performance to the penalised-sieve-estimation-based classifier-LASSO approach by Su et al. (2018), but are computationally easier. An application to a panel study of economic growth is also provided.

Modeling and Dynamic Analysis of a Slider-Crank Mechanism With Flexible Coupler and Joint

1991 ◽  
Author(s):  
Junghsen Lieh ◽  
Imtiaz Haque
Keyword(s):  
Dynamic Analysis ◽  
Virtual Work ◽  
Equations Of Motion ◽  
Joint Stiffness ◽  
Mechanism Model ◽  
Double Frequency ◽  
Varying Coefficients ◽  
Matrix Expansion ◽  
Time Varying Coefficients ◽  
Crank Mechanism

Abstract Modeling and dynamic analysis of a slider-crank mechanism with flexible joint and coupler is presented. The equations of motion of the mechanism model are formulated using a virtual work multibody formalism and cast in terms of a minimum set of generalized coordinates through a Jacobian matrix expansion. Numerical results show the influence of time-varying coefficients on the mechanism dynamic behavior due to a repeated task. The results illustrate that the joint motion and coupler deformation are highly coupled. The joint response is dominated by double frequency of input, however, the coupler deformation is influenced by the same frequency as that of excitation. Increase in joint stiffness tends to decrease the variations in coupler deformation.

Theoretical and Experimental Study of the Nonlinearly Coupled Heave, Pitch, and Roll Motions of a Ship in Longitudinal Waves

1993 ◽  
Author(s):  
I. G. Oh ◽  
A. H. Nayfeh ◽  
D. T. Mook
Keyword(s):  
Large Amplitude ◽  
Degrees Of Freedom ◽  
Excitation Frequency ◽  
Force Response ◽  
Governing Equations ◽  
Response Curves ◽  
Varying Coefficients ◽  
Jump Phenomena ◽  
Time Varying Coefficients ◽  
Three Degrees Of Freedom

Abstract The loss of dynamic stability and the resulting large-amplitude roll of a vessel in a head or following sea were studied theoretically and experimentally. A ship model with three degrees of freedom (roll, pitch, heave) was considered. The governing equations for the heave and pitch modes were linearized and their harmonic solutions were coupled with the nonlinear equation governing roll. The resulting equation, which has time-varying coefficients, was used to predict the response in roll. The principal parametric resonance was considered in which the excitation frequency is twice the natural frequency in roll. Force-response curves were obtained. The existence of jump phenomena and multiple stable solutions for the case of subcritical instability was observed in the experiments and found to be in good qualitative agreement with the results predicted by the theory. The experiments also revealed that the large-amplitude roll is dependent on the location of the model in the standing waves.

Vibration Control of a Beam Embedded With an Electrorheological Fluid

1995 ◽  
Author(s):  
Tyler J. Selstad ◽  
Kambiz Farhang ◽  
David Chelidze
Keyword(s):  
Control Method ◽  
Structural Member ◽  
Multiple Time Scales ◽  
Multiple Time ◽  
Parametric Stability ◽  
Stability Boundaries ◽  
Electrical Field Strength ◽  
Varying Coefficients ◽  
Time Varying Coefficients ◽  
Er Fluid

Abstract Electrorheological (ER) fluids are known to exhibit damping and stiffness properties which are highly dependent on the induced electrical field strength within the ER medium. Incorporation of ER fluid within a structural member then provides a means of stiffness and damping variation of the member. A structural member with embedded ER fluid is considered. Equations governing the axial and transverse motions of the member are reduced to a system of linear ordinary differential equations with time-varying coefficients. Application of the multiple time scales method results in amplitude-frequency relations. A control method is considered in which the effect of embedded ER fluid damping modulation using a simple harmonic excitation voltage on the parametric stability boundaries of the member is examined. Results indicate that the parametric stability boundaries can change effecting various modulation amplitudes and frequencies.

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