Stress transmission in cemented bidisperse granular materials

We analyze stress distributions in a two-dimensional bidisperse cemented granular packing for a broad range of the values of particle-size ratio, the volumes of large and small particles, and the amount of cementing matrix. In such textured porous materials, the stress concentration, which controls the fracture and fragmentation of the material under tensile loading or in grinding processes, reflects not only the porosity but also the contact network of the particle phase and the resulting stress chains. By means of peridynamic simulations under tensile loading, we show how both the texture and stress distribution depend on size ratio, volume ratio, and the amount of the cementing matrix. In particular, the volume fraction of the class of small particles plays a key role in homogenizing stresses across the system by reducing porosity. Interestingly, the texture controls not only the porosity but also the distribution of pores inside the system with its statistical variability, found to be strongly correlated with the homogeneity of stresses inside the large particles. The most homogeneous stress distribution occurs for the largest size ratio and largest volume fraction of small particles, corresponding to the lowest pore size dispersion and the cushioning effect of small particles and its similar role to the binding matrix for stress redistribution across the packing. At higher porosity, the tensile stresses above the mean stress fall off exponentially in all phases with an exponent that strongly depends on the texture. The exponential part broadens with decreasing matrix volume fraction and particle-size ratio. These correlations reveal the strong interplay between size polydispersity and the cohesive action of the binding matrix for stress distribution, which is significant for the behavior of textured materials in grinding operations.

On the effect of local sample slope during modulus measurements by contact-resonance atomic force microscopy

Contact-resonance atomic force microscopy (CR-AFM) is of great interest and very valuable for a deeper understanding of the mechanics of biological materials with moduli of at least a few GPa. However, sample surfaces can present a high topography range with significant slopes, where the local angle can be as large as  ± 50°. The non-trivial correlation between surface slope and CR-frequency hinders a straight-forward interpretation of CR-AFM indentation modulus measurements on such samples. We aim to demonstrate the significant influence of the surface slope on the CR-frequency that is caused by the local angle between sample surface and the AFM cantilever and present a practical method to correct the measurements. Based on existing analytical models of the effect of the AFM set-up's intrinsic cantilever tilt on CR-frequencies, we compute the non-linear variation of the first two (eigen)modes CR-frequency for a large range of surface angles. The computations are confirmed by CR-AFM experiments performed on a curved surface. Finally, the model is applied to directly correct contact modulus measurements on a durum wheat starch granule as an exemplary sample.

Auditory verbal hallucinations in first episode psychosis – an fMRI symptom capture study

Introduction

Neurobiological models of auditory verbal hallucination (AVH) have been advanced by symptom capture functional magnetic resonance imaging (fMRI), where participants self-report hallucinations during scanning. To date, regions implicated are those involved with language, memory and emotion. However, previous studies focus on chronic schizophrenia, thus are limited by factors, such as medication use and illness duration. Studies also lack detailed phenomenological descriptions of AVHs. This study investigated the neural correlates of AVHs in patients with first episode psychosis (FEP) using symptom capture fMRI with a rich description of AVHs. We hypothesised that intrusive AVHs would be associated with dysfunctional salience network activity.

Methods

Sixteen FEP patients with frequent AVH completed four psychometrically validated tools to provide an objective measure of the nature of their AVHs. They then underwent fMRI symptom capture, utilising general linear models analysis to compare activity during AVH to the resting brain.

Results

Symptom capture of AVH was achieved in nine patients who reported intrusive, malevolent and uncontrollable AVHs. Significant activity in the right insula and superior temporal gyrus (cluster size 141 mm3), and the left parahippocampal and lingual gyri (cluster size 121 mm3), P < 0.05 FDR corrected, were recorded during the experience of AVHs.

Conclusions

These results suggest salience network dysfunction (in the right insula) together with memory and language processing area activation in intrusive, malevolent AVHs in FEP. This finding concurs with others from chronic schizophrenia, suggesting these processes are intrinsic to psychosis itself and not related to length of illness or prolonged exposure to antipsychotic medication.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Intrinsic superoxide dismutase activity of MnO nanoparticles enhances the magnetic resonance imaging contrast

MnO nanoparticles decompose superoxide and hydrogen peroxide in an enzyme-like manner leading to enhanced MRI contrast.

[Neuralgia of the pudendal nerve following violent trauma: analgesia by pudendal neuromodulation]

Pudendal neuralgia is a neuropathic disease which is predominantly caused by pelvic trauma with pressure or stretching strain of the pudendal nerve. The Nantes criteria are used for the differential diagnostics of this disease and therapy includes pressure-relieving and analgesic measures using laparoscopic or open decompression procedures. This article reports the case of a female patient who developed pudendal neuralgia following violent trauma to the pelvic and urogenital regions. Due to the complexity of the symptoms combined sacral and pudendal neuromodulation (PNM) was carried out. A direct comparison of neuromodulative techniques revealed that PNM was superior resulting in almost complete freedom from pain. The PNM procedure could represent a therapeutic option for treatment of pudendal neuralgia.

Solid-phase organometallic synthesis

A solid-phase synthesis approach for a class of molybdenum carbonyl complexes has been developed. The system can be used to perform metal-complexation, ligand substitution reactions and oxidative eliminations on the solid phase and to cleave the final complexes under mild and selective conditions. Comparison is made to corresponding soluble complexes and liquid-phase reactions.

Development of an easy-to-use mass spectrometric technique to monitor solid-phase reactions on polystyrene supports

By using mass spectrometry as an analytical tool to characterise substituted, cross-linked polystyrene resins, it is possible to directly monitor the progress of the solid-phase reactions performed on these resins without prior cleavage of the resin-bound molecules. Therefore, this is a true on-resin analytical method. The mass-to-charge ratios observed in the mass spectra are readily assigned to fragments of the polymer that include the chemically bound substituents. This is the first time that the formation and breaking of bonds have been directly observed on the polymeric support. Furthermore, the relative intensities of the signals in the mass spectra provide a measure of the completeness of the reaction. Because these measurements are rapidly performed without further chemical transformations or cleavage procedures, and because only minimal amounts of material are needed, this technique could become the solid-phase equivalent of thin-layer chromatography used in classical liquid-phase chemistry.

Electronic Communication in C(4)-Bridged Binuclear Complexes with Paramagnetic Bisphosphane Manganese End Groups

Building blocks for conducting polymers or NLO materials are the linear, unsaturated carbon chain bridged manganese complexes 1(n+) (n=0-2). All oxidation states were investigated spectroscopically and by X-ray structure determinations. The analytical data confirm a communication of the electrons over the C(4) chain-a prerequisite for electrical conductivity and NLO properties of oligo- or polymeric materials.

A mathematical model of luteinizing hormone release from ovine pituitary cells in perifusion

We model the effect of gonadotropin-releasing hormone (GnRH) on the production of luteinizing hormone (LH) by the ovine pituitary. GnRH, released by the hypothalamus, stimulates the secretion of LH from the pituitary. If stimulus pulses are regular, LH response will follow a similar pattern. However, during application of GnRH at high frequencies or concentrations or with continuous application, the pituitary delivers a decreased release of LH (termed desensitization). The proposed mathematical model consists of a system of nonlinear differential equations and incorporates two possible mechanisms to account for this observed behavior: desensitized receptor and limited, available LH. Desensitization was provoked experimentally in vitro by using ovine pituitary cells in a perifusion system. The model was fit to resulting experimental data by using maximum-likelihood estimation. Consideration of smaller models revealed that the desensitized receptor is significant. Limited, available LH was significant in three of four chambers. Throughout, the proposed model was in excellent agreement with experimental data.

Effect of chloroquine on the degradation of L-fucose and the polypeptide moiety of plasma membrane glycoproteins

To evaluate the role of lysosomes in the breakdown of the carbohydrate and the polypeptide moiety of plasma membrane glycoproteins, degradation of the plasma membrane glycoprotein gp120 was studied in the liver of rats treated with the lysosomotropic amine chloroquine. Half-lives of degradation of the terminal sugar L-fucose and of L-methionine of gp120 were measured in isolated plasma membranes after pulse-chase experiments in vivo. Chloroquine extended the plasma membrane half-life of the polypeptide moiety of gp120 from 51 h to 143 h. By contrast, L-fucose of gp120 in the plasma membrane was not affected by chloroquine, but decayed with the same short half-lives of 22 h and 23 h in both controls and chloroquine-treated rats. The data suggest that the protein portion of gp120 is degraded within the lysosomes. Conversely, the terminal sugar L-fucose is removed from the glycoprotein independent from proteolysis before segregation of the glycoprotein into the lysosomal compartment.