Birkhoff’s Polytope and Unistochastic Matrices,N = 3 and N = 4

The set of bistochastic or doubly stochastic N×N matrices is a convex set called Birkhoff’s polytope, which we describe in some detail. Our problem is to characterize the set of unistochastic matrices as a subset of Birkhoff’s polytope. For N=3 we present fairly complete results. For N=4 partial results are obtained. An interesting difference between the two cases is that there is a ball of unistochastic matrices around the van der Waerden matrix for N=3, while this is not the case for N=4.     

Comparison of neutron emission spectra for D and DT plasmas with auxiliary heating

The DT experimental campaign on JET (1997) represents a major step forward for neutron emission spectroscopy (NES) diagnostic through the high quality data collected by the Magnetic Proton Recoil (MPR) spectrometer. These data for different DT plasma heating scenarios were analyzed here to determine the underlying fuel ion populations which in turn were used to project the 2.5-MeV neutron emission spectra for deuterium plasmas. The results on neutron spectra for DT and D plasmas in the same conditions were compared in order to determine the plasma information that could be expected from NES diagnosis of D plasmas and the instrumental characteristics that would be required. Future NES experiments would make dual sight line observations possible and the added diagnostic value is also assessed based on the present results.     

MRI measurements of the dependence on T1 of the echo amplitudes using a multiple spin-echo scheme

Analytical calculations using the Bloch formalism were performed to assess the dependence on T₁ of the echo amplitudes for the Phase-Alternating Phase-Shift (PHAPS) multiple spin-echo protocol. Measurements in a 0.5 T MR imaging unit were performed to ratify the analytical results. especially for low T₂ values, the echo amplitudes were erroneous, with an increasing contribution from stimulated echo components with increasing T₁. Apart from affecting T₂ estimates, stimulated echoes generated a non-monoexponential signal decay of the echo trains. The results confirmed previous simulation studies as regards the dependence on T₁ of T₂ estimates from PHAPS.     

Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 1. n-nonyl-beta-D-glucoside

The influence of salt, temperature, and deuterium oxide on the self-aggregation of n-nonyl-beta-D-glucoside (beta-C9G1) in dilute solution has been investigated by static and dynamic light scattering, neutron scattering, and tensiometry. Scattering data show that the micelles can be described as relatively stiff, elongated structures with a circular cross section. With a decrease of temperature, the micelles grow in one dimension, which makes it surprising that the critical micelle concentration (cmc) shows a concomitant increase. On the other hand, substitution of D2O for H2O causes a large increase in micelle size at low temperatures, without any appreciable effect on cmc. With increasing temperature, the deuterium effect on the micelle size diminishes. The effects of salt on the micelle size and cmc were found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreased according to the sequence SO4(2-) > Cl- > Br- > NO3- > I- > SCN-, whereas the effect on cmc displays the opposite trend. Here, I- and SCN are salting-in anions. Similarly, the effects of cations decrease with increasing polarizability in the sequence Li+ > Na+ > K+ > Cs+. At high ionic strength, the systems separate into two micellar phases. The results imply that the size of beta-C9G1 micelles is extremely sensitive to changes in the headgroup size. More specifically, temperature and salt effects on effective headgroup size, including intermolecular interactions and water ofhydration, are suggested to be more decisive for the micelle morphology than the corresponding effects on unimer solubility.     

Binding of surfactants to hydrophobically modified polymers

Recent progress in the understanding of the binding of surfactants to hydrophobically modified polymers (HMP), and the consequences of such binding, is reviewed. HMP are water-soluble polymers onto which low proportions of hydrophobic sidechains (hydrophobes) have been grafted. In an aqueous environment, the HMP hydrophobes associate among themselves and with added surfactant molecules into micelle-like aggregates. An HMP may therefore be considered as a ‘modified surfactant’, and the binding of surfactants to HMP is analogous to the mixed micellisation in mixed surfactant solutions. The binding isotherm gives the concentration of free (monomeric) surfactant and the stoichiometry of the HMP/surfactant complex at different total compositions. In mixtures involving ionic surfactants, it is found that the free surfactant often dominates, and gives important contributions to the ionic strength. Characteristic properties of HMP/surfactant mixtures may be related to stoichiometries of the mixed complexes. Thus, the maximum in solution viscosity, which is commonly found in HMP/surfactant mixtures, occurs at a similar hydrophobe stoichiometry (ratio of bound surfactant to HMP hydrophobe) for many different systems, although the total concentrations of surfactant at the maximum may vary by orders of magnitude, depending on the surfactant cmc. The solubility of a complex of oppositely charged HMP and surfactant is related to the charge stoichiometry of the complex. The phase separation/redissolution phenomena occurring in the bulk solution influence the HMP adsorption to surfaces and the forces between surfaces with adsorbed HMP.     

Studies of ligand-induced site-specific phosphorylation of epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase involved in the regulation of growth in many animal cells, including cancer cells. Phosphorylation of specific tyrosine residues within the cytoplasmic domain of EGFR is part of the initial activation process that occurs upon ligand binding, and these phosphotyrosine residues subsequently serve as docking sites for intracellular signaling molecules. To study the phosphorylation on each individual site, EGFR generated from a human epidermoid carcinoma cell line (A431) was analyzed by mass spectrometry. Liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) was used to identify the tryptic phosphopeptides and their sites of phosphorylation (Y992, Y1045, Y1068, Y1086, S1142, Y1148, and Y1173). Ion intensities for the phosphorylated and unphosphorylated tryptic peptides containing the sites of phosphorylation were measured, and the intensity ratios were used to assess the degree of phosphorylation at each site. Ligand concentrations were varied for epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) as stimuli, and all of the EGFR tyrosine sites were consequently found to exhibit increased levels of phosphorylation, although at different rates and to different extents. Phosphorylation of Y992 appeared to plateau at lower concentrations of ligand, whereas the other sites continued to have increased phosphorylation throughout a wide range of concentrations. Only small differences could be detected between the EGF and the TGF alpha-induced EGFR phosphorylation. Pretreatment of A431 cells with a small molecule EGFR inhibitor nearly eliminated the ligand-induced phosphorylation on all of the sites except for Y992 and Y1068.     

Quinolizidine-Based Variations and Antifungal Activity of Eight Lupinus Species Grown under Greenhouse Conditions

Fusarium oxysporum is an aggressive phytopathogen that affects various plant species, resulting in extensive local and global economic losses. Therefore, the search for competent alternatives is a constant pursuit. Quinolizidine alkaloids (QA) are naturally occurring compounds with diverse biological activities. The structural diversity of quinolizidines is mainly contributed by species of the family Fabaceae, particularly the genus Lupinus. This quinolizidine-based chemo diversity can be explored to find antifungals and even mixtures to address concomitant effects on F. oxysporum. Thus, the antifungal activity of quinolizidine-rich extracts (QREs) from the leaves of eight greenhouse-propagated Lupinus species was evaluated to outline promising QA mixtures against F. oxysporum. Thirteen main compounds were identified and quantified using an external standard. Quantitative analysis revealed different contents per quinolizidine depending on the Lupinus plant, ranging from 0.003 to 32.8 mg/g fresh leaves. Bioautography showed that all extracts were active at the maximum concentration (5 µg/µL). They also exhibited >50% mycelium growth inhibition. All QREs were fungistatic except for the fungicidal QRE of L. polyphyllus Lindl. Angustifoline, matrine, 13α-hydroxylupanine, and 17-oxolupanine were ranked to act jointly against the phytopathogen. Our findings constitute reference information to better understand the antifungal activity of naturally afforded QA mixtures from these globally important plants.     

High-resolution spectroscopic imaging of the human skin

High-resolution water, fat and chemical shift artefact-free images of different areas of the skin were obtained on a whole-body MR unit (1.5 T) with commercial receiver surface coil with a diameter of 25 mm and high-power gradients (23 mT/m). Sufficient signal-to-noise ratio was achieved by lowering receiver bandwidth to +/-10 kHz or lower and shortening the echo time to 11 (13) ms. Spectroscopic image data sets were acquired with resolution 0.102 x 0.133 mm in plane and slice thickness 0.5 mm. The results demonstrate that it is possible to produce high-quality water and fat micro-images of the skin layers using only a few chemical shift encoding steps in a clinically reasonable time (approximately 2 minutes per slice).