Comparison of 3-RPR planar parallel manipulators with?regard to their kinetostatic performance and sensitivity to geometric uncertainties

This paper deals with the sensitivity analysis of 3-RPR planar parallel manipulators. First, the manipulators under study as well as their degeneracy conditions are presented. Then, an optimization problem is formulated in order to obtain their maximal regular dexterous workspace. Moreover, the sensitivity coefficients of the pose of the manipulator moving platform to variations in the geometric parameters and in the actuated variables are expressed algebraically. Two aggregate sensitivity indices are determined, one related to the orientation of the manipulator moving platform and another one related to its position. Then, we compare two non-degenerate and two degenerate 3-RPR planar parallel manipulators with regard to their dexterity, workspace size and sensitivity. Finally, two actuating modes are compared with regard to their sensitivity.     

Porous polymer monoliths for small molecule separations: advancements and limitations

Porous polymer monoliths are considered to be one of the major breakthroughs in separation science. These materials are well known to be best suited for the separation of large molecules, specifically proteins, an observation most often explained by convective mass transfer and the absence of small pores in the polymer scaffold. However, this conception is not sufficient to explain the performance of small molecules. This review focuses in particular on the preparation of (macro)porous polymer monoliths by simple free-radical processes and the key events in their formation. There is special focus on the fluid transport properties in the heterogeneous macropore space (flow dispersion) and on the transport of small molecules in the swollen, and sometimes permanently porous, globule-scale polymer matrix. For small molecule applications in liquid chromatography, it is consistently found in the literature that the major limit for the application of macroporous polymer monoliths lies not in the optimization of surface area and/or modification of the material and microscopic morphological properties only, but in the improvement of mass transfer properties. In this review we discuss the effect of resistance to mass transfer arising from the nanoscale gel porosity. Gel porosity induces stagnant mass transfer zones in chromatographic processes, which hamper mass transfer efficiency and have a detrimental effect on macroscopic chromatographic dispersion under equilibrium (isocratic) elution conditions. The inherent inhomogeneity of polymer networks derived from free-radical cross-linking polymerization, and hence the absence of a rigid (meso)porous pore space, represents a major challenge for the preparation of efficient polymeric materials for the separation of small molecules.     

Development and practical application of a library of CID accurate mass spectra of more than 2,500 toxic compounds for systematic toxicological analysis by LC�CQTOF-MS with data-dependent acquisition

A library of collision-induced dissociation (CID) accurate mass spectra has been developed for efficient use of liquid chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) as a tool in systematic toxicological analysis. The mass spectra (Δm < 3 ppm) of more than 2,500 illegal and therapeutic drugs, pesticides, alkaloids, other toxic chemicals and metabolites were measured, by use of an Agilent 6530 instrument, by flow-injection of 1 ng of the pure substances in aqueous ammonium formate-formic acid-methanol, with positive and negative electrospray-ionization (ESI), selection of the protonated or deprotonated molecules [M+H](+) or [M-H](-) by the quadrupole, and collision induced dissociation (CID) with nitrogen as collision gas at CID energies of 10, 20, and 40 eV. The fragment mass spectra were controlled for structural plausibility, corrected by recalculation to the theoretical fragment masses and added to a database of accurate mass data and molecular formulas of more than 7,500 toxicologically relevant substances to form the "database and library of toxic compounds". For practical evaluation, blood and urine samples were spiked with a mixture of 33 drugs at seven concentrations between 0.5 and 500 ng mL(-1), prepared by dichloromethane extraction or protein precipitation, and analyzed by LC-QTOF-MS in data-dependent acquisition mode. Unambiguous identification by library search was possible for typical basic drugs down to 0.5-2 ng mL(-1) and for benzodiazepines down to 2-20 ng mL(-1). The efficiency of the method was also demonstrated by re-analysis of venous blood samples from 50 death cases and comparison with previous results. In conclusion, LC-QTOF-MS in data-dependent acquisition mode combined with an accurate mass database and CID spectra library seemed to be one of the most efficient tools for systematic toxicological analysis.     

Ultra-trace analysis of 36Cl by accelerator mass spectrometry: an interlaboratory study

A first international (36)Cl interlaboratory comparison has been initiated. Evaluation of the final results of the eight participating accelerator mass spectrometry (AMS) laboratories on three synthetic AgCl samples with (36)Cl/Cl ratios at the 10(-11), 10(-12), and 10(-13) level shows no difference in the sense of simple statistical significance. However, more detailed statistical analyses demonstrate certain interlaboratory bias and underestimation of uncertainties by some laboratories. Following subsequent remeasurement and reanalysis of the data from some AMS facilities, the round-robin data indicate that (36)Cl/Cl data from two individual AMS laboratories can differ by up to 17%. Thus, the demand for further work on harmonising the (36)Cl-system on a worldwide scale and enlarging the improvement of measurements is obvious.     

Toxicity of amorphous silica nanoparticles on eukaryotic cell model is determined by particle agglomeration and serum protein adsorption effects

Cell cultures form the basis of most biological assays conducted to assess the cytotoxicity of nanomaterials. Since the molecular environment of nanoparticles exerts influence on their physicochemical properties, it can have an impact on nanotoxicity. Here, toxicity of silica nanoparticles upon delivery by fluid-phase uptake is studied in a 3T3 fibroblast cell line. Based on XTT viability assay, cytotoxicity is shown to be a function of (1) particle concentration and (2) of fetal calf serum (FCS) content in the cell culture medium. Application of dynamic light scattering shows that both parameters affect particle agglomeration. The DLS experiments verify the stability of the nanoparticles in culture medium without FCS over a wide range of particle concentrations. The related toxicity can be mainly accounted for by single silica nanoparticles and small agglomerates. In contrast, agglomeration of silica nanoparticles in all FCS-containing media is observed, resulting in a decrease of the associated toxicity. This result has implications for the evaluation of the cytotoxic potential of silica nanoparticles and possibly also other nanomaterials in standard cell culture.     

Characterizing a spheroidal nanocage drug delivery vesicle using multi-detector hydrodynamic chromatography

The biological application of nanoparticles has resulted in an increased need for the development of robust, accurate, and precise methods for quality control analysis and characterization. Parameters such as particle size, particle shape, and their distributions affect end-use properties such as chemical reactivity, diffusivity, permeability, and transport. Introduced here is a hydrodynamic chromatography (HDC) method utilizing multi-angle static light scattering, quasi-elastic light scattering, differential viscometry, and differential refractometry detection for characterizing nanoscale vesicles. Quadruple-detector HDC was used to determine multiple sizing parameters and their statistical moments and distributions. Molar mass and molar mass averages were determined in a calibrant-independent fashion. Both the sizing parameters and the molar mass were measured across the HDC elution profile. The shape and structure of the nanoparticle were monitored as a function of HDC elution volume through the dimensionless ratio ??????R _G,z /R _H,z . The HDC results were comparable to those obtained by transmission electron microscopy, but more extensive characterization was possible by HDC, which provided distributions of both particle size and particle shape.

Sensoric potential of gold�Csilver core�Cshell nanoparticles

The sensitivities of five different core-shell nanostructures were investigated towards changes in the refractive index of the surrounding medium. The shift of the localized surface plasmon resonance (LSPR) maximum served as a measure of the (respective) sensitivity. Thus, gold-silver core-shell nanoparticles (NPs) were prepared with different shell thicknesses in a two-step chemical process without the use of any (possibly disturbing) surfactants. The measurements were supported by ultramicroscopic images in order to size the resulting core-shell structures. When compared to sensitivities of nanostructures reported in the literature with those of the (roughly spherical) gold-silver core-shell NPs, the latter showed comparable (or even higher) sensitivities than gold nanorods. The experimental finding is supported by theoretical calculation of optical properties of such core-shell NP. Extinction spectra of ideal spherical and deformed core-shell NPs with various core/shell sizes were calculated, and the presence of an optimal silver shell thickness with increased sensitivity was confirmed. This effect is explained by the existence of two overlapping plasmon bands in the NP, which change their relative intensity upon change of refractive index. Results of this research show a possibility of improving LSPR sensor by adding an extra metallic layer of certain thickness.     

Enhancement of strain-hardening by thermo-oxidative degradation of low-density polyethylene

Low-density polyethylene was thermally and thermo-oxidatively degraded at 170°C and subsequently characterized by linear-viscoelastic measurements and in uniaxial extension. The elongational viscosities measured were analyzed in the framework of the Molecular Stress Function (MSF) model. For the thermally degraded samples, degradation times between 2 and 6?h were applied. Formation of long-chain branching (LCB) evidenced by enhanced strain hardening was found to occur only during the first 2?h of thermal degradation. At longer exposure times, no difference in the level of strain hardening was observed. This was quantified by use of the MSF model, which in elongation has two model parameters: $f_{\max }^2$ determining the maximum relative stretch of the chain segments, and ?? representing the ratio of the molar mass of the (branched) polymer chain to the molar mass of the effective backbone alone. The non-linear parameter $f_{\max }^2$ increased from $f_{\max }^2 =14$ for the non-degraded sample to $f_{\max }^2 =22$ for the samples thermally degraded for 2 up to 6?h. For the thermo-oxidatively degraded samples, i.e. those degraded in the presence of air, degradation times between 30 and 90?min were applied. Surprisingly, under these degradation conditions, the level of strain hardening increases drastically up to $f_{\max }^2 =55$ with increasing exposure times from 30 up to 75?min due to LCB formation and then decreases for an exposure time of 90?min due to chain scission dominating LCB formation. The non-linear parameter ?? of the MSF model was found to be ???=?2 for all samples, indicating that the general type of the random branching structure remains the same under all degradation conditions. Consequently, only the parameter $f_{\max }^2$ of the MSF model and the linear-viscoelastic spectra were required to describe quantitatively the experimental observations. The strain hardening index, which is sometimes used to quantify strain hardening, was shown to follow accurately the trend of the MSF model parameter $f_{\max }^2$ .     

The Mesoscopic Eulerian Approach for Evaporating Droplets Interacting with Turbulent Flows

This paper presents a statistical approach, known as mesoscopic Eulerian formalism (Février et al., J Fluid Mech 533:1?C46, 2005), which is extended in order to model a cloud of inertial evaporating droplets interacting with a turbulent carrier flow. This approach is checked in a non-isothermal droplet-laden turbulent planar jet by means of a priori tests. The ??measurement?? of the mesoscopic particle-velocity and particle-temperature moments is accomplished by using the Eulerian particle fields computed from a Direct Numerical Simulation (DNS) coupled with a Lagrangian approach for the droplets. The results of this work show the ability of such an approach to describe the evaporating dispersed phase interacting with turbulent flows.     

On the role of lattice dynamics on low-temperature oxygen mobility in solid oxides: a neutron diffraction and first-principles investigation of {\hbox{L}}{{\hbox{a}}_2}{\hbox{Cu}}{{\hbox{O}}_{{4 + \delta }}}

The structure of oxygen-intercalated La₂CuO_4.07 has been investigated at 20 and 300?K by neutron diffraction on an electrochemically oxidized single crystal. At 20?K, reconstruction of the nuclear density by maximum entropy method shows strong displacements of the apical oxygen atoms towards [100] with respect to the F-centred unit cell, whilst displacements towards [110] and [100] were both found to be present at ambient temperature. Combining structural studies with first-principles lattice dynamical calculations, we interpret the displacements of the apical oxygen atoms to be at least partially of dynamic origin already at ambient temperature. Strong displacements of the apical oxygen atoms of stoichiometric and oxygen-doped $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ and corresponding associated lattice instabilities, i.e. low-energy phonon modes, are considered as a general prerequisite of low-temperature oxygen diffusion mechanisms. Lattice dynamical calculations on $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ suggest that the oxygen species diffusing at low temperature are not the interstitial but, more prominently, the apical oxygen atoms. The presence of interstitial oxygen atoms is, however, important to amplify via specific, low-energy phonon modes, a dynamic exchange mechanism between apical and vacant interstitial oxygen sites, thus allowing a dynamically triggered, shallow potential oxygen diffusion pathway. The crucial role of lattice dynamics to enable low-temperature oxygen mobility in K₂NiF₄-type oxides is discussed on a microscopic scale and compared to similar low-temperature oxygen diffusion mechanisms, recently proposed for non-stoichiometric oxides with Brownmillerite-type structure.