Do ternary liquid mixtures exhibit negative main Fick diffusion coefficients?

Measured main Fick diffusion coefficients are throughout positive. However, they may appear to be negative after transformation to the molar reference frame, if the excess volume is significant and the experimental uncertainties of the cross diffusion coefficients are large.

Diffusion in Multicomponent Liquids: From Microscopic to Macroscopic Scales

In spite of considerable research on the nature of aqueous alcohol mixtures that are characterized by microscopic inhomogeneity or incomplete mixing at the molecular level, transport properties have received little attention. We report the results of a study on diffusion in the ternary mixture of water with two alcohols, that is, water + methanol + ethanol, which is investigated on microscopic and macroscopic scales by means of molecular simulation and Taylor dispersion experiments. A novel protocol is developed for the comparison of mutual diffusion coefficients sampled by two fundamentally different approaches, which allows for their critical analysis. Because of complex intermolecular interactions, given by the presence of hydrogen bonding, the analysis of transport processes in this mixture is challenging for not only on the microscopic scale for simulation techniques but also on the macroscopic scale due to unfavorable optical properties. Binary limits of the Fick diffusion matrix are used for validation of the experimental ternary mixture results together with the verification of the validity of the phenomenological Onsager reciprocal relations. The Maxwell-Stefan diffusion coefficients and the thermodynamic factor are sampled by molecular simulation consistently on the basis of given force field models. The protocol for the comparison of the results from both approaches is also challenging because Fick diffusion coefficients of ternary mixtures depend on the frame of reference. Accordingly, the measured coefficients are transformed from the volume-averaged to the molar-averaged frame of reference, and it is demonstrated that both approaches provide not only similar qualitative behavior along two concentration paths but also strong quantitative agreement. This coordinated work using different approaches to study diffusion in multicomponent mixtures is expected to be a significant step forward for the accurate assessment of cross-diffusion.

Investigation of biokinetics of radioiodine with a population kinetics approach

The dosimetric studies required for planning individually tailored radioiodine therapy of benign thyroid pathologies may be too complex and time-demanding for many ordinary nuclear medicine departments. In this work, a preliminary population kinetics approach was applied to a model structure for iodine biokinetics in order to identify those model features that actually need to be individually investigated, in order to simplify the protocol for data collection in patients. Data from 29 patients undergoing radioiodine therapy for the treatment of the autonomous nodule syndrome were used in the analysis. The greatest inter-individual variations were observed in the parameters describing the transformation of iodide into organic iodine in the thyroid and in the kinetics of the organic form.

New calculations for internal dosimetry of beta-emitting radiopharmaceuticals

The calculation of absorbed dose from internally incorporated radionuclides is based on the so-called specific absorbed fractions (SAFs) which represent the fraction of energy emitted in a given source region that is absorbed per unit mass in a specific target organ. Until recently, photon SAFs were calculated using MIRD-type mathematical phantoms. For electrons, the energy released was assumed to be absorbed locally ('ICRP 30 approach'). For this work, photon and electron SAFs were derived with Monte Carlo simulations in the new male voxel-based reference computational phantom adopted by the ICRP and ICRU. The present results show that the assumption of electrons being locally absorbed is not always true at energies above 300-500 keV. For source/target organ pairs in close vicinity, high-energy electrons escaping from the source organ may result in cross-fire electron SAFs in the same order of magnitude as those from photons. Examples of organ absorbed doses per unit activity are given for (18)F-choline and (123)I-iodide. The impact of the new electron SAFs used for absorbed dose calculations compared with the previously used assumptions was found to be small. The organ dose coefficients for the two approaches differ by not more than 6 % for most organs. Only for irradiation of the urinary bladder wall by activity in the contents, the ICRP 30 approach presents an overestimation of approximately 40-50%.

Characterization of Streptococcus thermophilus lytic bacteriophages from mozzarella cheese plants

Phage infection still represents the main cause of fermentation failure during the mozzarella cheese manufacturing, where Streptococcus thermophilus is widely employed as starter culture. Thereby, the success of commercial lactic starter cultures is closely related to the use of strains with low susceptibility to phage attack. The characterization of lytic S. thermophilus bacteriophages is an important step for the selection and use of starter cultures. The aim of this study was to characterize 26 bacteriophages isolated from mozzarella cheese plants in terms of their host range, DNA restriction profile, DNA packaging mechanism, and the variable region VR2 of the antireceptor gene. The DNA restriction analysis was carried out by using the restriction enzymes EcoRV, PstI, and HindIII. The bacteriophages were distinguished into two main groups of S. thermophilus phages (cos- and pac-type) using a multiplex PCR method based on the amplification of conserved regions in the genes coding for the major structural proteins. All the phages belonged to the cos-type group except one, phage 1042, which gave a PCR fragment distinctive of pac-type group. Furthermore, DNA sequencing of the variable region VR2 of the antireceptor gene allowed to classify the phages and examine the correlation between typing profile and host range. Finally, bacterial strains used in this study were investigated for the presence of temperate phages by induction with mitomycin C and only S. thermophilus CHCC2070 was shown to be lysogenic.

Subterahertz superlattice parametric oscillator

We report a superlattice parametric oscillator (SPO), with a GaAs/AlAs superlattice as the active element. The SPO was pumped by a microwave field (power 4 mW) and produced third harmonic radiation at subterahertz frequencies (near 300 GHz; 0.1 mW). We attribute the parametric gain to the nonlinearity of the miniband transport.

Microstructure and rheology of yogurt made with cultures differing only in their ability to produce exopolysaccharides

Yogurt was made using an exopolysaccharide-producing strain of Streptococcus thermophilus and its genetic variant that only differed from the mother strain in its inability to produce exopolysaccharides. The microstructure was investigated using confocal scanning laser microscopy, allowing observation of fully hydrated yogurt and the distribution of exopolysaccharide within the protein network. Yogurt made with the exopolysaccharide-producing culture exhibited increased consistency coefficients, but lower flow behavior index, yield stress, viscoelastic moduli and phase angle values than did yogurt made with the culture unable to produce exopolysaccharide. The exopolysaccharides, when present, were found in pores in the gel network separate from the aggregated protein. These effects could be explained by the incompatibility of the exopolysaccharides with the protein aggregates in the milk. Stirring affected the yogurt made with exopolysaccharide differently from yogurt without exopolysaccharide, as it did not exhibit immediate syneresis, although the structural breakdown was increased. The shear-induced microstructure in a yogurt made with exopolysaccharide-producing culture was shown to consist of compartmentalized protein aggregates between channels containing exopolysaccharide, hindering syneresis as well as the buildup of structure after stirring.

Differences in baseline EEG measures for ADD and normally achieving preadolescent males

This study was designed as a replication of previous studies describing dynamic EEG differences between behaviorally dissimilar groups. This study is intended as a reference point from which other researchers can continue to establish the EEG correlates of "on-task" behavior. Eight Attention Deficit Disordered (ADD) children and eight Normally Achieving Controls (NAC) were assessed using dynamic EEG measures. Results are reported for the tasks of baseline (eyes open), reading, and drawing as recorded from FZ, CZ, PZ, C3, and C4. Significant amplitude differences between the groups were demonstrated in the theta band (4-8 hertz) during all tasks and for all sites. Amplitude differences in the beta band (12-20 hertz) were negligible. Differences between groups expressed as a ratio of theta/beta revealed significant differences mainly in the parietal region for on-task conditions. These results are discussed in relation to EEG neuro-feedback training paradigms and the importance of establishing normative "on-task" EEG values.

Sequencing and characterization of pST1, a cryptic plasmid from Streptococcus thermophilus

Eighty-six strains of S. thermophilus were examined for their plasmid content. Thirteen strains were found to contain one or two plasmids ranging in size from 2.1 to 7.4 kb. DNA-DNA hybridization analysis revealed the presence of five distinct groups of DNA homology. The complete nucleotide sequence of plasmid pST1 (Accession number X65856), which belongs to the major homology group, was determined. It has a molecular size of 2093 bp, a GC content of 35% and contains one major open reading frame of 945 bp (ORF A). The predicted protein, designated Rep A, showed sequence homology with replication proteins from a group of plasmids which are known to replicate via single-stranded DNA intermediates (ssDNA plasmids).