Statistician Heal Thyself: Have We Lost the Plot?

In 1984, Cleveland suggested that statisticians have an important role in changing the use of graphics in science for the better. Thirty years later, we compared graphs published in top-rated applied science and statistics journals, evaluated for overall quality and against five principles of graphical excellence. Nearly 40% of the 97 graphs we sampled were rated as poor, with no striking differences between the applied science and statistics graphs. Better use of graphs requires better definition of variables, units of measurement, scales, groups, and other graphical elements, and more routine use of grid lines on a “standard” set of graphical forms. Progress over the next 30 years needs to be supported by changes in software defaults.     

Chemorheology relations for epoxy-amine crosslinking

The goal of this study is to elucidate the relationship between the mechanism of bond formation, resulting structure, and the viscosity during the step polymerization of a thermoset. The system chosen for this work consists of a bifunctional epoxy, diglycidyl ether of bisphenol A, cured with a tetrafunctional amine, diaminodiphenyl sulfone. Steady shear and dynamic viscosity are measured as a function of extent of reaction throughout the epoxy-amine cure. Branching theory is used to relate the extent of reaction (i.e., conversion of epoxy groups) to certain structural parameters, including the weight-average molecular weight. The combination of the viscosity-conversion data with the branching theory enables the correlation between changes in rheological properties and network structure during polymerization. The steady shear viscosity rise is modeled as the product of a structure-dependent friction factor and weight-average molecular weight. The structural significance of the point in cure when the dynamic storage and loss modulus are equal (i.e., tan δ = 1) is also explored.     

Using Repertory Grids for Problem Construction

In the last couple of years, O.R. workers have expressed interest in the use of repertory grids as a part of their armoury for tackling messy problems in organizations. This paper is designed to describe some of our experiences of using grids to aid the process of problem construction. It will also express some of our views of the theoretical and technical aspects of their use for working on problems.The principles behind the use of grids invite the design of other methods for managing qualitative problem data. The paper will briefly introduce some we have found helpful.     

Electric field effects on insulin chain-B conformation

The response of proteins to different forms of stress continues to be a topic of major interest, especially with the proliferation of electromagnetic devices conjectured to have detrimental effects on human health. In this paper, we have performed molecular dynamics simulations on insulin chain-B under the influence of both static and oscillating electric fields, ranging from 10(7) to 10(9) V/m. We have found that both variants have an effect on the normal behavior of the protein, with oscillating fields being more disruptive to the structure as compared to static fields of similar effective strength. The application of a static field had a stabilizing effect on the secondary structure, restricting the inherent flexibility that is crucial for insulin's biological activity.     

Thermodynamics of protonation of AMP,ADP, and ATP from 50 to 125°C

The interaction of adenosine 5-monophosphate (AMP), adenosine 5-diphosphate (ADP), and adenosine 5-triphosphate (ATP) ions with protons in aqueous solution has been studied calorimetrically from 50 to 125°C and 1.52 MPa. At each temperature, the reaction of acidic AMP with tetramethylammonium hydroxide was combined with the heat of ionization for water to obtain the enthalpy of protonation of AMP, while the reactions of HCl with deprotonated tetramethylammonium salts of ADP and ATP were used to obtain the enthalpies of protonation of ADP and ATP. Equilibrium constant K, enthalpy change H^o, entropy change S^o, and heat capacity change C _p ^o values were calculated for the stepwise protonation reactions as a function of temperature. The reactions involving the first protonation of AMP, ADP, and ATP and the third protonation of ADP and ATP were endothermic over the temperature range studied, while that involving the second protonation is exothermic for AMP and ADP, but is exothermic below 100°C and endothermic at 125°C in the case of ATP. Consequently, log K values for the first and third protonation reactions (phosphate groups) increase while those for the second protonation reaction (N₁-adenine) decrease in the cases of AMP and ADP and go through a minimum in the case of ATP as temperature increases. The H^o values for all protonation reactions increase with temperature. The magnitude and the trend for the H^o, S^o, and C _p ^o values with temperature are discussed in terms of solvent-solute interactions. The magnitude of the C _p ^o values for the second protonation is consistent with little interaction between the phosphate ion and the protonated N₁ site of the adenine moiety in AMP, but indicates moderate interaction between these groups in ADP, and strong interaction in ATP.     

Quality control in combinatorial chemistry: determination of the quantity,purity, and quantitative purity of compounds in combinatorial libraries

The quality of combinatorial libraries determines the success of biological screening in drug discovery programs. In this paper, we evaluate and compare various methods for measuring identity, purity, and quantity (yield) of combinatorial libraries. Determination of quantitative purity reveals the true library quality and often indicates potential quality problems before full-scale library production. The relative purity can be determined for every member in a large library in a high-throughput mode, but must be cautiously interpreted. In particular, many impurities are not observable by relative purity measurements using detectors such as UV(214), UV(254), and evaporative light-scattering detection. These "invisible" impurities may constitute a significant portion of the sample weight. We found that TFA, plastic extracts, inorganic compounds, and resin washout are among these impurities. With compelling evidence, we reach a conclusion that purification is the only way to remove "invisible" impurities and improve the quantitative purity of any compound even though some compounds may have a high relative purity before purification.     

Detection of paralytic shellfish poison by rapid cell bioassay: antagonism of voltage-gated sodium channel active toxins in vitro

Although cytotoxicity assays provide several advantages over mouse bioassays, sodium channel-blocking marine toxins, such as those associated with paralytic shellfish poison (PSP), require prolonged incubation periods of 24-48 h. This is in marked contrast to in vitro detection of sodium channel-enhancing marine toxins such as ciguatoxins or brevetoxins which can be accomplished in as few as 4-6 h. We developed a modified PSP cell bioassay that is as rapid as in vitro methods for sodium channel-enhancing toxins. The cell bioassay is based on a saxitoxin-dependent antagonism of the rapid in vitro effects of brevetoxin or ciguatoxin. Comparative analysis of naturally incurred PSP residues by both antagonism cell bioassay and the mouse bioassay demonstrated significant correlation. The simplicity, sensitivity, and enhanced kinetics of the new antagonism cell bioassay format provide the basis for development of a practical alternative to conventional mouse testing for PSP.     

Enthalpies of Dilution of Aqueous Solutions of LiCl, KCl, and CsCl at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5 to 0.02m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.