Representing a scientific field: A bibliometric approach

A new bibliometric method is proposed for representing links between subfields as defined by a classification scheme. The frequency of co-occurrence of articles from different subfields in selected journals is used for measuring the degree of relatedness between these subfields. The results of such quantitative analysis could be compared to the tree topology of the classification network established in a qualitative analysis. The method is applied to describe the internal links within the field of condensed matter physics using the 1984 Physics Abstracts database. A distinction is made between experimental and theoretical links on the basis of treatment codes assigned to journal articles. The links described by cluster analysis are matched against the cross-reference network of the International Classification for Physics.     

Structural development of poly(ethylene terephthalate) during uniaxial stretching above the glass‐transition temperature: Study of the statistical influence of the stretching variables

In this article, we present an investigation of the structural development of poly(ethylene terephthalate) (PET) during uniaxial stretching above the glass‐transition temperature; this followed a statistical design of experiment approach to determine the influence of the stretching variables on the structural development. Amorphous PET was submitted to a stretching program with variations in the stretching temperature (T_st), stretching rate ( $\dot {\varepsilon}_{st}$ ), and stretching ratio (λ_st). Stretched samples were rapidly quenched and characterized by wide‐angle X‐ray scattering, optical birefringence, and differential scanning calorimetry. The relevance and influence of the stretching variables on the obtained parameters (phase fraction, phase orientation, and thermal parameters) were analyzed. The strain‐induced crystallinity was controlled by T_st, λ_st, and the interactions between them. Mesophase development was not dependant on T_st but on the interactions between $\dot {\varepsilon}_{st}$ and λ_st. The molecular orientation was proportionally dependent on T_st, λ_st, and their interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Device characteristics of a 10.1% hydrazine‐processed Cu2ZnSn(Se,S)4 solar cell

A power conversion efficiency record of 10.1% was achieved for kesterite absorbers, using a Cu₂ZnSn(Se,S)₄ thin‐film solar cell made by hydrazine‐based solution processing. Key device characteristics were compiled, including light/dark J–V, quantum efficiency, temperature dependence of V_oc and series resistance, photoluminescence, and capacitance spectroscopy, providing important insight into how the devices compare with high‐performance Cu(In,Ga)Se₂. The record kesterite device was shown to be primarily limited by interface recombination, minority carrier lifetime, and series resistance. The new level of device performance points to the significant promise of the kesterites as an emerging and commercially interesting thin‐film technology. Copyright © 2011 John Wiley & Sons, Ltd.     

Cosine tuning minimizes motor errors

Cosine tuning is ubiquitous in the motor system, yet a satisfying explanation of its origin is lacking. Here we argue that cosine tuning minimizes expected errors in force production, which makes it a natural choice for activating muscles and neurons in the final stages of motor processing. Our results are based on the empirically observed scaling of neuromotor noise, whose standard deviation is a linear function of the mean. Such scaling predicts a reduction of net force errors when redundant actuators pull in the same direction. We confirm this prediction by comparing forces produced with one versus two hands and generalize it across directions. Under the resulting neuromotor noise model, we prove that the optimal activation profile is a (possibly truncated) cosine--for arbitrary dimensionality of the workspace, distribution of force directions, correlated or uncorrelated noise, with or without a separate cocontraction command. The model predicts a negative force bias, truncated cosine tuning at low muscle cocontraction levels, and misalignment of preferred directions and lines of action for nonuniform muscle distributions. All predictions are supported by experimental data.     

Effect of urea on the polymer buffer solutions used for the electrophoretic separations of nucleic acids

The present study describes the effect of urea on the properties of hydroxyethyl cellulose (HEC) polymer solutions used for the separation of nucleic acids. Solution properties were investigated by viscosity measurements and supplemented by Raman spectroscopy of the solution components. By using viscosimetry, it was possible to identify that borate, urea, and HEC participate in an interaction causing an increase in the viscosity of dilute solutions. In addition, short polymer chains exhibited a 4-fold decrease in the entanglement threshold in the presence of 4 M urea and 0.356 M total borate concentration. These interactions were found to be specific to HEC. Raman spectroscopy monitored serial addition of 8 M urea to HEC sieving solutions combined with factor analysis indicated formation of minor urea species. Lack of change in the Raman spectrum and relative amount of borate suggested that there is no direct interaction between borate and urea. These effects on HEC sieving solution properties lead to the use of low HEC concentrations that are beneficial for the separation of nucleic acids under denaturing conditions.     

Stable, soluble T-cell receptor molecules for crystallization and therapeutics

Antibody and T-cell receptors (TCRs) are the primary recognitionmolecules of the adaptive immune system. Antibodies have beenextensively characterized and are being developed for a largenumber of therapeutic applications. This has been possible becauseof the ability to manufacture stable, soluble, monoclonal antibodieswhich retain the antigen specificity of B cells. Unlike antibodies,TCRs are not expressed in a soluble form, but are anchored tothe T-cell surface by an insoluble trans-membrane domain. Characterizationand development of TCRs has been hampered by the lack of suitablemethods for producing them as soluble and stable proteins. Herewe report the engineering of soluble human TCRs suitable forcrystallization studies and potentially for in vivo therapeuticuse. Received March 11, 2003; revised July 1, 2003; accepted July 30, 2003.