A Note on Cell Wall and Wood Substance Densities

The differences in reported values of material densities for wood are discussed and analyzed with respect to cell-wall voids. A model is proposed to account for the reported differences and for general use in calculating relationships between wood volume and density

Polymerization of Methyl Methacrylate by Heat-Catalyst and Gamma-Irradiation Methods

Methyl methacrylate (MMA) was bulk-polymerized with 0 to 4% crosslinker (ethylene glycol dimethacrylate, EGDM, and trimethylol propane trimethacrylate, TMPTM), initiated with 0.05 to 5% catalyst (Vazo) at 65-75 C or 0.1 to 1 Mrad/hr gamma radiation at 20 C. Heat-catalyzed MMA conversion to polymer vs. time was obtained directly from polymer mass, which indicated that about 90% conversion had occurred at the exothermic peak temperature. The time to the exothermic peak temperature was used to determine sample polymerization time. The over-all polymerization rate varied with the half-power of initiator concentration. An Arrhenius plot of the initiator-time data gave an activation energy of 18 kcal/mole. A log-log relationship was found between crosslinker concentration and polymerization time over the 65-75 C temperature and 0.1-0.4% initiator range. The crosslinkers were found equally efficient in reducing polymerization time. Peak exothermie temperature varied directly with time, irrespective of the initiator and crosslinker concentrations or bath temperature except as they affected time. In the irradiation tests, the crosslinkers exhibited different data fits: log-log with EGDM and semilog for TMPTM. The time-dose rate equation for uncrosslinked MMA was analogous to that for heat-catalyzed polymerization. Molecular weight of uncrosslinked PMMA was determined as a function of temperature and catalyst concentration, and dose rate. Similar molecular weights were obtained for heat-catalyzed polymerization at 65 C and gamma irradiation at 20 C for numerically the same initiator concentration (%) and does rate (Mrad/hr)

Longitudinal Diffusion and Permeability of Nonpolar Gases in Eastern Hemlock

Longitudinal ethane diffusion and nitrogen permeability were measured in oven-dry eastern hemlock sapwood. Samples were selected from 2 trees, 3 heights, and 4 quadrants, and either air- or solvent-dried for aspirated or unaspirated conditions. An IR method was used to detect ethane concentration in nitrogen at 25 C from which diffusion coefficients were calculated. The mean diffusion coefficient of the solvent-dried samples was 40% of free diffusion; the air-dried coefficient was about 16% of the free diffusion coefficient. No significant differences were found between position in the tree or oven-dry density and the diffusion coefficients. Diffusion coefficients were used to determine tortuosity differences in air- and solvent-dried wood. Effective pore openings obtained from permeability measurements, the Klinkenberg equation, and the temperature coefficient of diffusion confirmed that diffusion was occurring in the Kundsen end of the slip-flow region. A linear relationship was found between the permeability constant and diffusion coefficient. Diffusion and permeability measurements produce separate and complementary data that can be used to determine the mode of conductivity of gases in wood

Dynamic Mechanical Behavior of Black Cherry (Prunus Serotina EHRH.)

The dynamic mechanical properties of black cherry (Prunus serotina Ehrh.) have been investigated as a function of temperature at audio frequencies. Relaxation processes are evident near 200, 360, and 510 K. The process near 200 K was investigated as a function of initial moisture content (based on mass measurements prior to testing). At moisture contents greater than about 20%, the damping peak is centered near 185 K. This relaxation shifts with moisture content, and at moisture contents below 6%, the peak is centered near 225 K. The relaxation in the 360 K region is also associated with initial moisture content. For oven-dry black cherry specimens, the dynamic mechanical properties in the 360 K region are nearly temperature-independent. The relaxation near 510 K is believed to be associated with thermal degradation of wood constituents that are known to degrade in that temperature region

Thermogravimetric Evaluation of Fungal Degradation of Wood

Yellow birch (Betula alleghaniensis Brit.) was degraded by a white rot fungus (Polyporus versicolor L. ex Fr.; now Coriolus versicolor (L.) Quél.) and a brown rot fungus (Poria monticola Murr.; now Poria placenta (Fr.) Cke.) under controlled conditions. Samples of known weight loss from fungi were milled to pass a 40-mesh screen, oven-dried, and then measured for rate of mass loss over selected temperature ranges. Rates of mass loss of nominal 4-mg samples were obtained isothermally in flowing oxygen using a thermo-gravimetric (TG) system containing a Cahn electrobalance. Activation energy (E) was found using zero-order kinetics for the initial mass loss. White-rotted birch (to 60% weight loss) had an E of 35 to 43 kcal/mole over the range of approximately 190 to 210 C. On the basis of TG data, the weight loss from fungal attack could be predicted within about 5%. Brown-rotted birch had more variation in E (30 to 44 kcal/mole), over a temperature range of 170 to 195 C. The rate of mass loss of brown-rotted birch (to 52% weight loss) was more sensitive to temperature because of the known nonlinear decrease in cellulose DP during fungal attack. Dynamic thermogravimetry, a much simpler method, indicated a similar degree of instability from fungal attack as did the isothermal tests. TG appears to be a viable research method to evaluate fungal attack of wood

Some Physical Properties of Birch Carbonized in A Nitrogen Atmosphere

The dynamic mechanical properties, mass loss, and shrinkage data of birch carbonized in a nitrogen atmosphere to different temperatures from 473 to 973 K have been investigated. The dynamic elastic modulus data decreased as the heat treatment temperatures approached 673 K. Major mass loss and shrinkage accompanied the decrease in the modulus data. Treatments at higher temperatures (> 673 K) produced substantially less additional mass loss and shrinkage but produced increased rigidity in the char. The internal friction behavior of the char was complex

Realism, Objectivity, and Evaluation

I discuss Benacerraf's epistemological challenge for realism about areas like mathematics, metalogic, and modality, and describe the pluralist response to it. I explain why normative pluralism is peculiarly unsatisfactory, and use this explanation to formulate a radicalization of Moore's Open Question Argument. According to the argument, the facts -- even the normative facts -- fail to settle the practical questions at the center of our normative lives. One lesson is that the concepts of realism and objectivity, which are widely identified, are actually in tension

Thermophysical optimization of specialized concrete pavement materials for collection of surface heat energy and applications for shallow heat storage

There is great potential to use pavement structures to collect and/or store solar energy for the heating and cooling of adjacent buildings, e.g. airport terminals, shopping malls, etc. Therefore, pavement materials comprising both conventional and unconventional concrete mixtures with a wide range of densities, thermal conductivities, specific heat capacities, and thermal diffusivities were investigated. Their thermo-physical properties were then used as inputs to a one dimensional transient heat transport model in order to evaluate the temperature changes at the various depths at which heat might be abstracted or stored. The results indicated that a high diffusivity pavement, e.g. incorporating high conductive aggregates and/or metallic fibres, can significantly enhance heat transfer as well as reduction of thermal stresses across the concrete slab. On the other hand a low diffusivity concrete can induce a more stable temperature at shallower depth enabling easier heat storage in the pavement as well as helping to reduce the risk of damage due to freeze-thaw cycling in cold regions

FCNC in left-right symmetric theories and constraints on the right-handed scale

We revise the limits on the FCNC higgses in manifestly left-right symmetric theories. It is shown that the combination of the Kobayashi-Maskawa CP-violation with the tree level $\Delta S=2$ higgs exchange gives very large contribution to the CP-violating $\epsilon$ parameter. It leads to the new strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of the order $\sqrt{m_t/m_c}$. Being addressed to the supersymmetric left-right models, FCNC problem requires both right-handed scale and supersymmetric mass parameters be heavier than 50 TeV for $tan\beta\sim 1$. The most relaxed case corresponds to $tan\beta\sim 20- 30$ where right-handed scale can be of the order of few TeV.Comment: 11 pages, latex, 3 figure