Treesearch

An assemblage of permineralized woods from the Miocene Bakate Formation, Fejej Plain, Ethiopia, is described. This assemblage of twelve wood types differs from other Miocene wood assemblages known from Ethiopia. Cell wall percentages of the woods were determined to estimate the original specific gravities of the woods in order to better understand the Miocene vegetation and environment of Fejej. The relatively high specific gravities (0.63 to 0.82) and numerous and narrow vessels of these Miocene woods are characteristics of dry deciduous forests or woodlands. The affinities of some of the...

We make use of Cramer conditions together with the well-known local quadratic convergence of Newton?s method to establish the asymptotic closeness of k-step Newton estimators to efficient likelihood estimators. In Verrill and Johnson [2007. Confidence bounds and hypothesis tests for normal distribution coefficients of variation. USDA Forest Products Laboratory Research Paper FPL-RP-638], we use this result to establish that estimators based on Newton steps from [square root]n- consistent estimators may be used in place of efficient solutions of the likelihood equations in likelihood ratio,...

The allowable-stress design methodology that has been used for decades to design timber bridge superstructures is being replaced in the near future. Beginning in October 2007, bridge designers will be required by the Federal Highway Administration (FHWA) to utilize the Load and Resistance Factor Design (LRFD) design specifications published by the American Association of State Transportation and Highway Officials (AASHTO). Until recently, significant discrepancies existed between the two design methodologies as they pertain to the design of timber bridges. However, several modifications...

This work will briefly review published literature and current research activities on the corrosion of metals in contact with wood treated with waterborne alternatives to CCA. In addition, recommendations to minimize these corrosive effects in timber bridges will be discussed.

Xylose is a major constituent of plant lignocellulose, and its fermentation is important for the bioconversion of plant biomass to fuels and chemicals. Pichia stipitis is a well-studied, native xylose-fermenting yeast. The mechanism and regulation of xylose metabolism in P. stipitis have been characterized and genes from P. stipitis have been used to engineer xylose metabolism in Saccharomyces cerevisiae. We have sequenced and assembled the complete genome of P. stipitis. The sequence data have revealed unusual aspects of genome organization, numerous genes for bioconversion, a preliminary...

At its fundamental level, wood is made up of nanodimensional cellulose nanocrystalline fibrils that have extremely high strength?approximately 25% the strength of carbon nanotubes. Because of this, plus our emerging ability to manipulate cell wall nano- dimensional architecture and functionality, the abundance of lignocellulosic materials, and our emerging ability to self-assemble nanodimensional materials into macro-scale materials and products, we can expect that forest products will emerge as ?the material of the 21st Century? just as steel was in the 19th Century and plastics in the...

This paper reviews previous reports on the moisture content of wood exposed above ground and compares those values to moisture contents obtained using simulated rainfall and immersion methods. Laboratory leaching trials with CCA-treated specimens were also conducted and the results compared to published values for leaching of CCA-treated specimens exposed above ground outdoors. Previous researchers have reported that the moisture content of wood exposed above ground may range from over 80% to minimums of approximately 10%. In most studies, the maximum moisture content fell within 40% to...

Structural assessment of in-place wood floors is currently limited to inspection of individual members. This is costly and laborious. Consequently, the continued use or adaptive reuse of old/historic buildings is often in jeopardy because of the lack of an efficient and economical assessment method. A systems approach of assessment is the subject of this research. Floors in four old buildings and several laboratory-built floors were tested. The floor?s bending stiffness was determined by static bending tests and its fundamental natural frequency was determined by transverse forced vibration...

A modified version of the Midwest Guardrail System (MGS), utilizing small-diameter round wood posts, was developed, tested, and evaluated. Three systems were developed using different species of timber, Douglas Fir, Ponderosa Pine, and Southern Yellow Pine. A combination of Barrier VII computer simulation modeling and several series of cantilever bogie tests, conducted in both a rigid sleeve and soil, were used to determine the required diameter of post for each species in order to serve as an equivalent substitute for the standard steel post used in the barrier system. The final recommende...

Hybrid composites of wood flour/kenaf fiber and polypropylene were prepared at a fixed fiber to plastic ratio of 40 : 60 and variable ratios of the two reinforcements namely 40 : 0, 30 : 10, 20 : 20, 10 : 30, and 0 : 40 by weight. Polypropylene was used as the polymer matrix, and 40–80 mesh kenaf fiber and 60–100 mesh wood flour were used as the fiber and the particulate reinforcement, respectively. Mixing process was carried out in an internal mixer at 180°C at 60 rpm. ASTM D 638 Type 1 tensile specimens of the composites were produced b injection molding. Static tensile tests were...