Off-farm Work, Technical Efficiency, and Production Risk: Empirical Evidence from a National Farmer Survey in Taiwan

The objective of this paper is to investigate the differences in yield production, production efficiency, and yield risk for farmers with and without off-farm work. Using a nationwide survey of Taiwanese rice farmers, we estimate a stochastic production frontier model accommodating the technical inefficiency and the production risk simultaneously. Applying the stochastic dominance criterion to rank the estimated technical efficiency and yield risk between professional farmers and farmers with off-farm jobs, our empirical analysis shows that off-farm work is significantly associated with lower technical efficiency. Additionally, farmers with off-farm work face higher production risks. Comparing the marginal effects of input uses on technical inefficiency and yield risk between these groups of farmers, we found a substantial heterogeneity of input uses between these two groups of farmers.Off-farm work, technical efficiency, production risk, Taiwan, Crop Production/Industries, Farm Management,

Migration, Social Security, and Economic Growth

This paper studies the effect of population aging on economic performance in an overlapping-generations model with international migration. Fertility is endogenized so that immigrants and natives can have different fertility rates. Fertility is an important determinant to the tax burden of social security since it affects the quantity and quality of future tax payers. We find that introducing immigrants into the economy can reduce the tax burden of social security. If life expectancy (or the replacement ratio) is high enough, the growth rate of GDP per worker for an economy with international migration will be higher than for a closed economy. Regarding migration policies, our numerical results indicate that economic growth rate of GDP per worker will first decrease then increase as the flow of immigrants increases. Increasing the quality of immigrants will enhance economic growth.Economic growth; Fertility; Migration; Social security.

RISK AVERSION, UNCERTAINTY AVERSION, AND VARIATION AVERSION IN APPLIED COMMODITY PRICE ANALYSIS

Standard models of hedging behavior assume that either hedgers wish to minimize net price variation or they wish to balance variation versus profits. These models treat variation as risk and fail to distinguish between variation that is random and variation that is not random over time. Newer models of decision making differentiate between random and nonrandom variation somewhat, but they inadequately distinguish variation from risk. This paper reviews the distinctions among variation, uncertainty, and risk and calculates optimal hedge ratios for two models addressing the distinction. Empirical optimal hedge ratios typically decline toward zero when variation aversion is included in the models. These results may help explain why hedgers commonly hedge less than recommended by the standard models.Demand and Price Analysis, Marketing,

Experimental evidence for new symmetry axis of electromagnetic beams

The new symmetry axis of a well-behaved electromagnetic beam advanced in paper Physical Review A 78, 063831 (2008) is not purely a mathematical concept. The experimental result reported by Hosten and Kwiat in paper Science 319, 787 (2008) is shown to demonstrate the existence of this symmetry axis that is neither perpendicular nor parallel to the propagation axis.Comment: 10 pages and 3 figure

The Multiplicative Inverse Eigenvalue Problem over an Algebraically Closed Field

Let $M$ be a square matrix and let $p(t)$ be a monic polynomial of degree $n$. Let $Z$ be a set of $n\times n$ matrices. The multiplicative inverse eigenvalue problem asks for the construction of a matrix in $Z$ such that the product matrix $MZ$ has characteristic polynomial $p(t)$. In this paper we provide new necessary and sufficient conditions when $Z$ is an affine variety over an algebraically closed field.Comment: 9 Page

Quantum Versus Jahn-Teller Orbital Physics in YVO3_3 and LaVO3_3

We argue that the large Jahn-Teller (JT) distortions in YVO$_3$ and LaVO$_3$ should suppress the quantum orbital fluctuation. The unusual magnetic properties can be well explained based on LDA+$U$ calculations using experimental structures, in terms of the JT orbital. The observed splitting of the spin-wave dispersions for YVO$_3$ in C-type antiferromagnetic state is attributed to the inequivalent VO$_2$ layers in the crystal structure, instead of the ``orbital Peierls state''. Alternative stacking of $ab$-plane exchange couplings produces the c-axis spin-wave splitting, thus the spin system is highly three dimensional rather than quasi-one-dimensional. Similar splitting is also predicted for LaVO$_3$, although it is weak.Comment: 4 pages, 2 tables, 2 figures, (accepted by PRL

STM Studies of TbTe3: Evidence for a fully Incommensurate Charge Density Wave

We observe unidirectional charge density wave ordering on the cleaved surface of TbTe3 with a Scanning Tunneling Microscope at ~6 K. The modulation wave-vector q_{CDW} as determined by Fourier analysis is 0.71 +/- 0.02 * 2 pi/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of ~(1/3) * 2 pi/a ordering perpendicular to the CDW. Our analysis indicates that the CDW is incommensurate.Comment: 4 pages, 4 figure

Photon reabsorption in fluorescent solar collectors

Understanding photon transport losses in fluorescence solar collectors is very important for increasing optical efficiencies. We present an analytical expression to characterize photon reabsorption in fluorescent solar collectors, which represent a major source of photon loss. A particularly useful universal form of this expression is found in the limit of high reabsorption, which gives the photon reabsorption probability in a simple form as a function of the absorption coefficient and the optical étendue of the emitted photon beam. Our mathematical model predicts fluorescence spectra emitted from the collector edge, which are in excellent agreement with experiment and provide an effective characterization tool for photon transport in light absorbing media

Nature of the Quantum Phase Transition in Quantum Compass Model

In this work, we show that the quantum compass model on an square lattice can be mapped to a fermionic model with local density interaction. We introduce a mean-field approximation where the most important fluctuations, those perpendicular to the ordering direction, are taken into account exactly. It is found that the quantum phase transition point at $J_x=J_z$ marks a first order phase transition. We also show that the mean field result is robust against the remaining fluctuation corrections up to the second order.Comment: 7 pages, 10 fig