A simplification of the terpolymerization equation

The terpolymerization composition equation has been modified to eliminate the consideration of interactions between monomers 2 and 3 when they are present in low concentration in the feed mixture relative to monomer 1. Terpolymers with a wide variety of comonomers and compositions have been synthesized and used to demonstrate that a simplified terpolymerization equation accurately predicts terpolymer composition.     

Dollar vs. percentage markup pricing schemes under a dominant retailer

We investigate two very common pricing schemes for a Stackelberg-dominant retailer: percentage-markup and dollar-markup. We show that when a dominant retailer switches from dollar to percentage markup, the channel’s “overall pie” and the retailer’s “pie-piece” are both enlarged. In contrast, the manufacturer will be forced to levy a lower wholesale price, thus receiving a smaller pie-piece despite the larger pie. The preceding statements hold regardless of whether the demand is deterministic or stochastic. However, the effects of switching to percentage markup on the retail price and sales volume will depend not only on whether the demand is stochastic, but also on the assumed demand-curve shape and on whether demand stochasticity is “additive” or “multiplicative”. Besides presenting a comprehensive set of answers on the comparative performance of dollar- and percentagemarkups, our results also highlight the often overlooked importance of choosing between: (i) dollar- and percentage-markup; and (ii) the formats of the assumed stochasticity and demand curves.     

Early discovery of individual firm insolvency

Email: wxding{at}uic.edu Received on 11 January 2006. Accepted on 21 November 2006. This paper proposes a new methodology for the early discoveryof individual firm insolvency without employing any other firm'sdata. The proposed individual-level model can be applied todifferent firms, regardless of industry type or asset size,and thereby overcomes the sample selection problem commonlyfound in aggregate-level prediction models. Unlike many previousstudies, which assume that the distributions of variables involveddo not change over time and that the variables follow a singleknown distribution, the proposed model can capture each individualfirm's potential multiple data-generating processes and determinethe actual distributions exhibited in its own data. Thus, itcaptures each individual firm's intrinsic heterogeneity. Anempirical study illustrates the greater predictive power ofthis model compared with the current conventional methods. Specifically,the predictive accuracy of the proposed model is 92.65% and77.45% for 2 and 5 years prior to actual bankruptcy, respectively.Moreover, the proposed model is adaptive and simple to implement.     

Development of the Cantonese speech intelligibility index

A Speech Intelligibility Index (SII) for the sentences in the Cantonese version of the Hearing In Noise Test (CHINT) was derived using conventional procedures described previously in studies such as Studebaker and Sherbecoe [J. Speech Hear. Res. 34, 427-438 (1991)]. Two studies were conducted to determine the signal-to-noise ratios and high- and low-pass filtering conditions that should be used and to measure speech intelligibility in these conditions. Normal hearing subjects listened to the sentences presented in speech-spectrum shaped noise. Compared to other English speech assessment materials such as the English Hearing In Noise Test [Nilsson et al., J. Acoust. Soc. Am. 95, 1085-1099 (1994)], the frequency importance function of the CHINT suggests that low-frequency information is more important for Cantonese speech understanding. The difference in ,frequency importance weight in Chinese, compared to English, was attributed to the redundancy of test material, tonal nature of the Cantonese language, or a combination of these factors.     

Grating-assisted phase matching in extreme nonlinear optics

We propose a new technique for phase matching high harmonic generation that can be used for generating bright, tabletop, tunable, and coherent x-ray sources at keV photon energies. A weak quasi-cw counterpropagating field induces a sinusoidal modulation in the phase of the emitted harmonics that can be used for correcting the large plasma-induced phase mismatch. We develop an analytical model that describes this grating-assisted x-ray phase matching and predicts that very modest intensities (<10(10) W/cm2) of quasi-cw counterpropagating fields are required for implementation.     

Quantitation of 8-hydroxydeoxyguanosine in DNA by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry

A methodology has been developed and validated for quantifying 8-hydroxydeoxyguanosine (8-OHdG) in both commercial DNA and DNA isolated from livers of male Sprague-Dawley rats by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry. The analytical method conditions, including conditions for stabilizing 8-OHdG during complex nuclease P1 enzymatic digestion, were also evaluated. The limit of detection for 8-OHdG was 1.0 ng/mL (17.6 fmol on-column), and the linearity of the calibration curve was greater than 0.998 from 1.0 to 500 ng/mL. The intraday assay precision relative standard deviation (RSD) value for quality control (QC) samples was < or =5.59% with accuracies ranging from 91.84 to 117.61%. The interday assay precision (RSD) value was < or =1.76% with accuracies ranging from 91.84 to 116.67%. This method, combined with the LC/UV analysis of deoxyguanosine (dG), was used for determination of the levels of 8-OHdG/10(6) dG in DNA nuclease P1 enzymatic hydrolysates from both commercial DNA and rat liver DNA.     

Dynamic docking of cytochrome b5 with myoglobin and alpha-hemoglobin: heme-neutralization "squares" and the binding of electron-transfer-reactive configurations

Intracomplex electron transfer (ET) occurs most often in intrinsically transient, low affinity complexes. As a result, the means by which adequate specificity and reactivity are obtained to support effective ET is still poorly understood. We report here on two such ET complexes: cytochrome b5 (cyt b5) in reaction with its physiological partners, myoglobin (Mb) and hemoglobin (Hb). These complexes obey the Dynamic Docking (DD) paradigm: a large ensemble of weakly bound protein-protein configurations contribute to binding in the rapid-exchange limit, but only a few are ET-active. We report the ionic-strength dependence of the second-order rate constant, k2, for photoinitiated ET from within all four combinations of heme-neutralized Zn deuteroporphyrin-substituted Mb/alphaHb undergoing ET with cyt b5, the four "corners" of a "heme-neutralization square". These experiments provide insights into the relative importance of both global and local electrostatic contributions to the binding of reactive configurations, which are too few to be observed directly. To interpret the variations of k2 arising from heme neutralization, we have developed a procedure by which comparisons of the ET rate constants for a heme-neutralization square permit us to decompose the free energy of reactive binding into individual local electrostatic contributions associated with interactions between (i) the propionates of the two hemes and (ii) the heme of each protein with the polypeptide of its partner. Most notably, we find the contribution from the repulsion between propionates of partner hemes to the reactive binding free energy to be surprisingly small, DeltaG(Hb) approximately +1 kcal/mol at ambient temperature, 18 mM ionic strength, and we speculate about possible causes of this observation. To confirm the fundamental assumption of these studies, that the structure of a heme-neutralized protein is unaltered either by substitution of Zn or by heme neutralization, we have obtained the X-ray structure of ZnMb prepared with the porphyrin dimethyl ester and find it to be nearly isostructural with the native protein.