Political Pressure: An Examination of U.S. Senators’ Actions in Restricting Canadian Softwood Lumber Imports

interest groups, lumber industry, political contributions, U.S.-Canada softwood lumber dispute., International Relations/Trade,

Population Growth and Land Use Dynamics along Urban–Rural Gradient

In this study we apply a spatial conditional logit model to determine factors influencing land cover change in three contiguous counties in West Georgia between 1992 and 2001 using point (pixel) based observations of land characteristics. We found that accessibility to population and population growth affect not only development of rural lands and transition between agricultural and forestry uses, but also influence changes between forest types. The model could be used to project land use–land cover change at watershed or subwatershed level and thus serve as a valuable tool for county and city planners.conditional logit, land use change, population gravity index, spatial lag, Agribusiness, Labor and Human Capital, Land Economics/Use, Q15, Q23, R14,

Four positive periodic solutions of a discrete time delayed predator–prey system with nonmonotonic functional response and harvesting

AbstractIn this paper, by employing the continuation theorem of coincidence degree theory, we establish an easily verifiable criteria for the existence of at least four positive periodic solutions for a discrete time delayed predator–prey system with nonmonotonic functional response and harvesting

SOCIOECONOMIC INFLUENCES ON LAND USE CHOICE AT WATERSHED LEVEL: A MULTINOMIAL LOGIT ANALYSIS OF LAND USE DISTRIBUTION IN WEST GEORGIA

Allocation of fixed proportion of land to developed, forest, agricultural and other land uses in a watershed was modeled as an optimization problem faced by a single user. A multinomial logit model was used to estimate the effects of urbanization, demographic structure, personal income and spatial distribution of watersheds.Land Economics/Use,

Property taxes: do they affect forestry and agricultural land uses

Abstract , NRI point data. The model tilizes modern land use theory based on the land rent theory. In addition to the returns, we ey words: land use change, property tax, discrete choice, nested logit, Louisiana

Different Functions of the Insect Soluble and Membrane-Bound Trehalase Genes in Chitin Biosynthesis Revealed by RNA Interference

BACKGROUND: Trehalase, an enzyme that hydrolyzes trehalose to yield two glucose molecules, plays a pivotal role in various physiological processes. In recent years, trehalase proteins have been purified from several insect species and are divided into soluble (Tre-1) and membrane-bound (Tre-2) trehalases. However, no functions of the two trehalases in chitin biosynthesis in insects have yet been reported. PRINCIPAL FINDINGS: The membrane-bound trehalase of Spodoptera exigua (SeTre-2) was characterized in our laboratory previously. In this study, we cloned the soluble trehalase gene (SeTre-1) and investigated the tissue distribution and developmental expression pattern of the two trehalase genes. SeTre-1 was expressed highly in cuticle and Malpighian tubules, while SeTre-2 was expressed in tracheae and fat body. In the midgut, the two trehalase genes were expressed in different locations. Additionally, the expression profiles of both trehalase mRNAs and their enzyme activities suggest that they may play different roles in chitin biosynthesis. The RNA interference (RNAi) of either SeTre-1 or SeTre-2 was gene-specific and effective, with efficiency rates up to 83% at 72 h post injection. After RNAi of SeTre-1 and SeTre-2, significant higher mortality rates were observed during the larva-pupa stage and pupa-adult stage, and the lethal phenotypes were classified and analyzed. Additionally, the change trends of concentration of trehalose and glucose appeared reciprocally in RNAi-mutants. Moreover, knockdown of SeTre-1 gene largely inhibited the expression of chitin synthase gene A (CHSA) and reduced the chitin content in the cuticle to two-thirds relative to the control insects. The chitin synthase gene B (CHSB) expression, however, was inhibited more by the injection of dsRNA for SeTre-2, and the chitin content in the midgut decreased by about 25%. CONCLUSIONS: SeTre-1 plays a major role in CHSA expression and chitin synthesis in the cuticle, and SeTre-2 has an important role in CHSB expression and chitin synthesis in the midgut

A van der Waals pn heterojunction with organic/inorganic semiconductors

van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials have attracted tremendous attention due to their excellent electrical/optical properties and device applications. However, current 2D heterojunctions are largely limited to atomic crystals, and hybrid organic/inorganic structures are rarely explored. Here, we fabricate hybrid 2D heterostructures with p-type dioctylbenzothienobenzothiophene (C8-BTBT) and n-type MoS2. We find that few-layer C8-BTBT molecular crystals can be grown on monolayer MoS2 by vdW epitaxy, with pristine interface and controllable thickness down to monolayer. The operation of the C8-BTBT/MoS2 vertical heterojunction devices is highly tunable by bias and gate voltages between three different regimes: interfacial recombination, tunneling and blocking. The pn junction shows diode-like behavior with rectifying ratio up to 105 at the room temperature. Our devices also exhibit photovoltaic responses with power conversion efficiency of 0.31% and photoresponsivity of 22mA/W. With wide material combinations, such hybrid 2D structures will offer possibilities for opto-electronic devices that are not possible from individual constituents.Comment: 16 pages, 4 figure