On the changes in the microwave dielectric spectrum of aqueous phospholipid bilayer solutions at the ordered-fluid phase transition

The microwave part of the dielectric spectrum (ν ? 1 GHz) is considered of aqueous phospholipid solutions in the limit of high water content. A continuum model is presented which allows to calculate in the water relaxation region the frequency-dependent complex permittivity of solutions in which the bilayers form globular single-walled vesicles as well as multilamellar liposomes. The model is not only capable of explaining the strikingly small values of the extrapolated static permittivity and of the main dielectric relaxation time which became evident in many measurements on colloidal aqueous solutions of phospholipids. It also allows the positive and negative step-like changes in the dielectric properties of solutions, which have been found at the main (order-disorder) phase transition temperature of the bilayers, to be explained by dimensional changes as resulting from vesicle growth and fusion.     

On the inclusion of collisional correlations in quantum dynamics

We present a formalism to describe collisional correlations responsible for thermalization effects in finite quantum systems. The approach consists in a stochastic extension of time dependent mean field theory. Correlations are treated in time dependent perturbation theory and loss of coherence is assumed at some time intervals allowing a stochastic reduction of the correlated dynamics in terms of a stochastic ensemble of time dependent mean-fields. This theory was formulated long ago in terms of density matrices but never applied in practical cases because of its complexity. We propose here a reformulation of the theory in terms of wave functions and use a simplified 1D model of cluster and molecules allowing to test the theory in a schematic but realistic manner. We illustrate the performance in terms of several observables, in particular global moments of the density matrix and single particle entropy built on occupation numbers. The occupation numbers remain fixed in time dependent mean-field propagation and change when evaluating the correlations, then taking fractional values. They converge asymptotically towards Fermi distributions which is a clear indication of thermalization.     

Time-asymptotic boson states from infinite mean field quantum systems coupled to the boson gas

By means of cocycle techniques in a recent paper, the global dynamics of mean field-boson couplings has been studied. Here, by restricting to the bosonic system the infinite time limit (t ) for very general initial states, one obtains time-asymptotic states on the bosonicC ^*-Weyl algebra, in which one partially rediscovers the collective ordering of the infinite mean field lattice.     

The low temperature magnetic phase diagram of EuxSr1−xTiO3

Specific heat and magnetization measurements demonstrate that the antiferromagnetic (AFM) phase transition at T _N  = 5.7 K of EuTiO₃ is rapidly suppressed with Sr doping in Eu _x Sr_1?x TiO₃. Close to x = 0.25, T _N  = 0 K and AFM order vanishes. Above this critical concentration a finite transition temperature to an AFM phase is observed. The exchange couplings are derived as a function of x and the corresponding low temperature phase diagram is presented.     

A Preisach-based hysteresis model for magnetic and ferroelectric hysteresis

In this paper we present a model for hysteretic nonlinearities with non-local memories. This model can be applied to describe hysteretic material behavior. Common applications are ferromagnetic or ferroelectric materials. Our model consists of an analytic function and a Preisach operator. We define a continuous Preisach weight function and introduce a method for the identification of the model parameters. The model parameters are customized to a set of symmetric hysteresis curves. We verify our model for a soft magnetic material, a hard magnetic material and the ferroelectric behavior of some piezoelectric material. After that, non-symmetric curves like the virgin curve are predicted very well by the model. It is especially useful, if forced magnetization or polarization, that appears beyond technical saturation, come into account.     

Grüneisen parameter of NaCl at high compressions

A new method of determining the pressure dependence of the Grüneisen parameter is described. The measurements were carried out on NaCl to 33 kbar at room temperature using an end-loaded piston-cylinder apparatus. A fluid cell arrangement with Bridgman unsupported area seals was used. Changes of sample temperature associated with small adiabatic pressure changes were measured and the Grüneisen parameter could be calculated from the thermodynamic relationship $\text{γ = (}\text{K}{}_{\mathrm{s}}\text{T}\text{)(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}$ where K_s is the adiabatic bulk modulus. Our results are in excellent agreement with those reported by Roberts and Ruppin [1] who calculated the pressure dependence of γ from thermodynamic and ultrasonic data and in excellent agreement with those reported by Hardy and Karo [2] who carried out a lattice-dynamical calculation.     

Automated,high performance,flow-through chemiluminescence microarray for the multiplexed detection of phycotoxins

A novel multiplexed immunoassay for the analysis of phycotoxins in shellfish samples has been developed. Therefore, a regenerable chemiluminescence (CL) microarray was established which is able to analyze automatically three different phycotoxins (domoic acid (DA), okadaic acid (OA) and saxitoxin (STX)) in parallel on the analysis platform MCR3. As a test format an indirect competitive immunoassay format was applied. These phycotoxins were directly immobilized on an epoxy-activated PEG chip surface. The parallel analysis was enabled by the simultaneous addition of all analytes and specific antibodies on one microarray chip. After the competitive reaction, the CL signal was recorded by a CCD camera. Due to the ability to regenerate the toxin microarray, internal calibrations of phycotoxins in parallel were performed using the same microarray chip, which was suitable for 25 consecutive measurements. For the three target phycotoxins multi-analyte calibration curves were generated. In extracted shellfish matrix, the determined LODs for DA, OA and STX with values of 0.5 ± 0.3 μg L⁻¹, 1.0 ± 0.6 μg L⁻¹, and 0.4 ± 0.2 μg L⁻¹ were slightly lower than in PBS buffer. For determination of toxin recoveries, the observed signal loss in the regeneration was corrected. After applying mathematical corrections spiked shellfish samples were quantified with recoveries for DA, OA, and STX of 86.2%, 102.5%, and 61.6%, respectively, in 20 min. This is the first demonstration of an antibody based phycotoxin microarray.     

Chemiluminescence microarrays in analytical chemistry: a critical review

Multi-analyte immunoassays on microarrays and on multiplex DNA microarrays have been described for quantitative analysis of small organic molecules (e.g., antibiotics, drugs of abuse, small molecule toxins), proteins (e.g., antibodies or protein toxins), and microorganisms, viruses, and eukaryotic cells. In analytical chemistry, multi-analyte detection by use of analytical microarrays has become an innovative research topic because of the possibility of generating several sets of quantitative data for different analyte classes in a short time. Chemiluminescence (CL) microarrays are powerful tools for rapid multiplex analysis of complex matrices. A wide range of applications for CL microarrays is described in the literature dealing with analytical microarrays. The motivation for this review is to summarize the current state of CL-based analytical microarrays. Combining analysis of different compound classes on CL microarrays reduces analysis time, cost of reagents, and use of laboratory space. Applications are discussed, with examples from food safety, water safety, environmental monitoring, diagnostics, forensics, toxicology, and biosecurity. The potential and limitations of research on multiplex analysis by use of CL microarrays are discussed in this review. Figure

Achievements in the development of CL microarray analysis platforms