How Overdrying Wood Reduces Its Bonding to Phenol-Formaldehyde Adhesives: A Critical Review of the Literature. Part I. Physical Responses

This review critically evaluates literature on the ways in which excessive drying (overdrying) inactivates wood surfaces to bonding, primarily for phenolic adhesives. In Part I of a two-part review, three inactivation mechanisms involving physical responses to overdrying are considered: (1) exudation of extractives to the surface, which lowers the wettability or hides the surface; (2) reorientation of wood surface molecules, which reduces wettability or places for bonding; and (3) irreversible closure of large micropores in cell walls. I believe that extensive evidence from wood bonding and paper sizing research supports the mechanism of extractives-induced low wettability as the cause for inactivation of Douglas-fir and southern pines. Molecular reorientation and irreversible micropore closure are proposed wood inactivation mechanisms that involve loss of wettability and bonding sites

Cure of Phenol-Formaldehyde Adhesive in the Presence of CCA-Treated Wood by Differential Scanning Calorimetry

Chromated copper arsenate (CCA) preservatives interfere with bond formation of phenolic-based adhesives on CCA-treated southern pine. Ions of chromium (Cr+3) and copper (Cu+2) are known to complex with phenol and formaldehyde, affecting the rate of cure of the resin. Differential scanning calorimetry (DSC) was used to thermally analyze the cure of a commercial phenol-formaldehyde adhesive in the presence or CCA-treated wood, solutions of CCA preservative, and solutions of model compounds containing ions of Cr+6, Cr+3, Cu+2, and As+5. The DSC thermograms indicated that free metallic ions in solution can accelerate the cure of a portion of the adhesive at less than normal temperatures. However, when the CCA preservative was chemically "fixed" within the southern pine wood, accelerated cure of the adhesive did not occur

Improving the fatigue resistance of adhesive joints in laminated wood structures

The premature fatigue failure of a laminated wood/epoxy test beam containing a cross section finger joint was the subject of a multi-disciplinary investigation. The primary objectives were to identify the failure mechanisms which occurred during the finger joint test and to provide avenues for general improvements in the design and fabrication of adhesive joints in laminated wood structures

Reactivity of Hydroxymethylated Resorcinol Coupling Agent as it Affects Durability of Epoxy Bonds to Douglas-fir

Epoxy adhesives develop strong bonds to wood, but they lack the structural durability to withstand the severe stresses from repeated water soaking and drying. Research at the Forest Products Laboratory led to a discovery that hydroxymethylated resorcinol (HMR) physicochemically couples to both epoxy adhesive and lignocellulosics of wood to produce bonds that are extraordinarily resistant to dclamination. The HMR coupling agent is quite reactive at room temperatures; therefore, the length of its reaction time, or the time between preparing the solution and applying it to the wood surface, strongly influences the durability of adhesion. The experiments in this study defined the optimum range of reaction time when adhesion is maximum for epoxy bonds to HMR-primed Douglas-fir. Heats of reaction (by differential scanning calorimetry), molecular-size distribution (by gel permeation chro-matography), and chemical structures of HMR (by carbon-13 nuclear magnetic resonance spectros-copy) are described for this range of optimum reaction times

Genetically Determined Plasma Lipid Levels and Risk of Diabetic Retinopathy: A Mendelian Randomization Study.

Results from observational studies examining dyslipidemia as a risk factor for diabetic retinopathy (DR) have been inconsistent. We evaluated the causal relationship between plasma lipids and DR using a Mendelian randomization approach. We pooled genome-wide association studies summary statistics from 18 studies for two DR phenotypes: any DR (N = 2,969 case and 4,096 control subjects) and severe DR (N = 1,277 case and 3,980 control subjects). Previously identified lipid-associated single nucleotide polymorphisms served as instrumental variables. Meta-analysis to combine the Mendelian randomization estimates from different cohorts was conducted. There was no statistically significant change in odds ratios of having any DR or severe DR for any of the lipid fractions in the primary analysis that used single nucleotide polymorphisms that did not have a pleiotropic effect on another lipid fraction. Similarly, there was no significant association in the Caucasian and Chinese subgroup analyses. This study did not show evidence of a causal role of the four lipid fractions on DR. However, the study had limited power to detect odds ratios less than 1.23 per SD in genetically induced increase in plasma lipid levels, thus we cannot exclude that causal relationships with more modest effect sizes exist

Production of π0 and η mesons in Cu+Au collisions at sNN =200 GeV

Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in e+e- collisions in a range of collision energies sNN=3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu+Cu collisions either does not affect the jet fragmentation into light mesons or it affects the π0 and η the same way

L\'evy-stable two-pion Bose-Einstein correlations in sNN=200\sqrt{s_{_{NN}}}=200 GeV Au++Au collisions

We present a detailed measurement of charged two-pion correlation functions in 0%-30% centrality $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from L\'evy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter $\lambda$, the L\'evy index of stability $\alpha$ and the L\'evy length scale parameter $R$ as a function of average transverse mass of the pair $m_T$. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same L\'evy-stable source functions. The $\lambda(m_T)$ measurements indicate a decrease of the strength of the correlations at low $m_T$. The L\'evy length scale parameter $R(m_T)$ decreases with increasing $m_T$, following a hydrodynamically predicted type of scaling behavior. The values of the L\'evy index of stability $\alpha$ are found to be significantly lower than the Gaussian case of $\alpha=2$, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.Comment: 448 authors, 25 pages, 11 figures, 4 tables, 2010 data. v2 is version accepted for publication in Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Systematic study of charged-pion and kaon femtoscopy in Au++Au collisions at sNN\sqrt{s_{_{NN}}}=200 GeV

We present a systematic study of charged pion and kaon interferometry in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.Comment: 499 authors, 27 pages, 13 figures, and 11 tables. v2 is the version accepted for publication in Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm