Differential scanning calorimetry characterization of urea–formaldehyde resin curing behavior as affected by less desirable wood material and catalyst content

Differential scanning calorimetry was applied to investigate the curing behavior of urea–formaldehyde (UF) resin as affected by the catalyst content and several less desirable wood materials (e.g., wood barks, tops, and commercial thinnings). The results indicate that the reaction enthalpy of UF resin increased with increasing catalyst content. The activation energy and peak temperature of the curing UF resin generally decreased with increasing catalyst content at lower levels of catalyst content. However, with further increases in catalyst content, the changes in the activation energy and peak temperature were very limited to nonexistent. The hydrolysis reaction of the cured UF resin occurred during the latter stages of the curing process at both lower level (<0.2%) and higher level (>0.7%) catalyst contents. This indicates that there existed an optimal range of catalyst content for the UF resin. The curing enthalpy of the UF resin decreased with increasing wood raw materials present due to the effect of diffusion induced by the wood materials and the changes in the phase of the curing systems. This suggests that the curing reactions reached a lower final degree of conversion for the wood–resin mixtures than for the UF resin alone. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2027–2032, 2005     

Peat adsorption of herbicide 2,4-D from wastewaters

The possibility of utilizing peat as adsorbent for removal of the pesticide 2,4-D from contaminated wastewaters has been evaluated in this investigation. Batch tests were conducted at different conditions of initial solute concentration, pH, particle size of adsorbent, temperature and ratios of weight of adsorbent to solution volume, in order to determine the optimum range of these variables for the adsorption operation. Removal ratios for the 2,4-D of the order of 90% were obtained under optimum conditions. The adsorption of 2,4-D in peat is described adequately by the Freundlich isotherm. Continuous tests, utilizing adsorption columns, were then conducted in order to determine the design parameters for a proposed treatment plant. The column tests were adequately correlated by the Bohart-Adams equation.     

Role of olfaction in host finding by aphid parasitoidAphidius nigripes (Hymenoptera: Aphidiidae)

The olfactory responses of the parasitoidAphidius nigripes Ashmead were investigated with a four-field airflow olfactometer. Female and male parasitoids did not respond to potato plants, the food plant of their host. However, females were strongly attracted by odors from a preferred host,Macrosiphum euphorbiae (Thomas), and also from less preferred hosts such asMyzus persicae (Sulzer) andAphis nasturtii Kalt. Moreover,A. nigripes females responded positively to odors from a nonhost aphid,Rhopalosiphum maidis Fitch. The honeydew produced by these four aphid species was also very attractive to females. Males did not respond to aphids or honeydew but were highly attracted by odors from conspecific female parasitoids.Contribution No. 394 from the Département de biologie, Université Laval.     

Electrolytic production of hydrogen from aqueous acidic methanol solutions

The electrochemical production of hydrogen (H₂) from liquid methanol in acidic aqueous media was investigated in a proton exchange membrane (PEM) electrolyser, comprising a two-compartment glass cell with a membrane electrode assembly (MEA) composed of a Nafion^® 117 membrane and gas diffusion electrodes (GDE). Methanol electrolysis was studied at concentrations ranging from 0 to 16 M, where 0 M corresponds to water electrolysis. The influence of catalysts (Pt and Pt–Ru), catalyst support (C or black), operating temperatures (23, 50 and 75 °C) and operating modes (dry and wet cathode) were evaluated in the static mode. A theoretical thermodynamic analysis of the system was done as a function of temperature. The limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined.     

Sociotropy/autonomy and vulnerability to specific life events in patients with unipolar depression and bipolar disorders.

Followed samples of unipolar and bipolar patients for a 6-month period, with independent assessment of symptoms and life events. Patients were initially categorized into subtypes using Beck's Sociotropy/Autonomy Scale, with the prediction that onset or exacerbation of symptoms, as well as more total symptoms, would occur for sociotropic individuals experiencing more negative interpersonal events than achievement events, and for autonomous-achievement patients experiencing more achievement events than interpersonal events. Results were confirmed for unipolars, indicating that the course of disorder was associated with the occurrence of personally meaningful life events, but not for bipolars. Further research is recommended to examine whether the effect is equally robust for both subtypes of unipolars, whether longer study duration may be required for bipolars, and whether a cognitive self-schema mechanism may account for the specific vulnerability to a subset of stressful events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An examination of college students' willingness to experience consequences as a unique predictor of alcohol problems.

The focus of the study was to examine (1) the unique variance between willingness to experience specific consequences (e.g., vomit) and reported experience of the consequence after controlling for drinking, and (2) the relationships between consequence specific constructs (attitudes and norms) and willingness to experience specific consequences in the context of a structural equation model. Freshmen students (n = 167) from a large northeastern university were randomly selected to participate. Results indicated willingness to experience consequences accounted for significant variance across consequence outcomes controlling for drinking. Significant relationships were observed between consequence specific constructs (attitudes and norms) and students' willingness to experience consequences. Findings provide empirical support that alcohol-related consequences have multiple determinants and are not only a function of alcohol consumption. Prevention efforts may benefit from a more comprehensive approach that includes both drinking and consequence-specific constructs as targets of change. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Bias and variability of diagnostic spectral parameters extractedfrom closing sounds produced by bioprosthetic valves implanted in themitral position

A method is proposed to estimate the bias and variability of eight diagnostic spectral parameters extracted from mitral closing sounds produced by bioprosthetic heart valves. These spectral parameters are: the frequency of the dominant (F1) and second dominant (F2) spectral peaks, the highest frequency of the spectrum found at -3 dB (F-3), -10 dB (F-10) and -20 dB (F-20) below the highest peak, the relative integrated area above -20 dB of the dominant peak (RIA20), the bandwidth at -3 dB of the dominant spectral peak (BW3), and the ratio of F1 divided by BW3 (Q1). The bias and variability of four spectral techniques were obtained by comparing parameters extracted from each technique with the parameters of a spectral "standard." This "standard" consisted of 19 normal mitral sound spectra computed analytically by evaluating the Z transform of a sum of decaying sinusoids on the unit circle. Truncation of the synthesized mitral signals and addition of random noise were used to simulate the physiological characteristics of the closing sounds. Results show that the fast Fourier transform method with rectangular window provides the best estimates of F1 and Q1, that the Steiglitz-McBride method with maximum entropy (pole-zero modeling with four poles and four zeros) can best evaluate F2, F-20, RIA20 and BW3, and that the all-pole modeling with covariance method (16 poles) is best suited to compute F-3. It was also shown that both the all-pole modeling and the Steiglitz-McBride methods can be used to estimate F-10. It is concluded that a single algorithm would not provide the best estimates of all spectral parameters.     

RF circuit implications of moderate inversion enhanced linear region in MOSFETs

The implications for radio frequency circuit design of the nonlinear behavior of a MOSFET transistor over all regions of operation, including moderate inversion region, are investigated. Third-order intermodulation distortion in a MOSFET amplifier is analyzed by means of Volterra Series representation. Analysis and measurements reveal a significant peaking, or "sweet-spot" of the third-order intercept point in the moderate inversion region. As a result, a significant increase in linearity with low power consumption is possible. Analysis and measurements shows the dependance of distortion on the frequency, and transistor parameters, as well as the effects of the load impedance and feedback.