On strongly equivalent context-free grammar forms

It is shown that the set of all interpretations of one (or of all) context-free grammar forms modulo strong equivalence is a distributive lattice with respect to the ordering relation “is an interpretation of”. It is also established that for each context-free grammar form there exists a unique (up to “pseudo-isomorphism”) symbol-tight, strongly equivalent context-free grammar form which is minimal with respect to the number of productions.     

Concise description of finite languages

This paper is a contribution to the theory of grammatical complexity, in particular to the following basic question: consider some language L and grammars of some type X; what is the smallest number of productions of a type X grammar required to generate L? This complexity measure, the so-called X complexity of L, has been investigated before. We study the more basic case when the languages L considered are finite (a case which has been neglected, so far). We obtain a number of results and insights suggesting that such study is of importance. In addition to a number of ‘expected’ (but not necessarily easy to prove) results that with type X grammars more productions are necessary than with some other type Y grammars (even if types X and Y define the same family of languages) we show that if the limit of certain sequences of finite languages is of type X₁ then the type X complexity of each of the finite languages involved must be low.     

Pressure‐Sensitive Adhesive Blend Films for Low‐Tack Applications

Polymer blend films consisting of a tacky and a nonadhesive component are promising candidates for low‐tack applications. Immiscibility of both components results in a phase separation process yielding a tacky matrix with glassy objects embedded. The influence of the blending ratio of the components poly(n‐butyl acrylate) (PnBA) and polystyrene (PS) is addressed. The mechanical information resulting from the tack test shows the possibility of varying the bonding strength of the PSA blend over a wide range. The macroscopic and microscopic structural characterization with optical microscopy and ultrasmall angle X‐ray scattering (USAXS) shows that the blend PnBA/PS exhibits similarities to common filler systems as well as deviates regarding installed structures. Due to the large domain size on a microscopic level, only the tacky component, PnBA, defines the adhesive behavior. The nonadhesive component limits the contact area between the adhesive and the substrate.

     

Systematic comparison of bias and precision data obtained with multiple-point and one-point calibration in six validated multianalyte assays for quantification of drugs in human plasma

One-point (linear through zero) calibration is often used as a compromise between necessary calibration, workload, and time. The aim of the present study was to systematically check the applicability of one-point calibration by comparing bias and precision data obtained with full and one-point calibration. Data from validation studies of six mass spectrometry-based multianalyte bioanalytical assays were used for this purpose. Bias and intermediate precision datasets of full multiple-point calibration were compared to six one-point calibration datasets (A-F in rising calibrator concentration order) calculated from the same raw data. The datasets were statistically compared using the Friedman test followed by Dunn's multiple comparison test. The results obtained with full calibration and the different one-point calibrations were found to differ significantly (P < 0.05) in all of the six studied methods. The best one-point calibration results were obtained with calibrator D, with which acceptance criteria for bias and precision were fulfilled for the majority of analytes. However, some extremely high bias and precision data were obtained for some analytes in the low-concentration range. In conclusion, one-point calibration with a calibrator close to the center of the full calibration range can be a feasible alternative to full calibration.     

Hydrogen permeation and diffusion in densified MOF-5 pellets

The metal-organic framework Zn₄O (BDC)₃ (BDC = 1,4-bezene dicarboxlate), also known as MOF-5, has demonstrated considerable adsorption of hydrogen, up to 7 excess wt.% at 77 K. Consequently, it has attracted significant attention for vehicular hydrogen storage applications. To improve the volumetric hydrogen density and thermal conductivity of MOF-5, prior studies have examined the hydrogen storage capacities of dense MOF-5 pellets and the impact of thermally conductive additives such as expanded natural graphite (ENG). However, the performance of a storage system based on densified MOF-5 powders will also hinge upon the rate of hydrogen mass transport through the storage medium. In this study, we further characterize MOF-5 compacts by measuring their hydrogen transport properties as a function of pellet density (ρ = 0.3–0.5 g cm⁻³) and the presence/absence of ENG additions. More specifically, the Darcy permeability and diffusivity of hydrogen in pellets of neat MOF-5, and composite pellets consisting of MOF-5 with 5 and 10 wt.% ENG additions, have been measured at ambient (296 K) and liquid nitrogen (77 K) temperatures. The experimental data suggest that the H₂ transport in densified MOF-5 is strongly related to the MOF-5 pellet density ρ.