Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003? substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.     

Kinetic modulation of pulsed chronopotentiometric polymeric membrane ion sensors by polyelectrolyte multilayers

Polymeric membrane ion-selective electrodes are normally interrogated by zero current potentiometry, and their selectivity is understood to be primarily dependent on an extraction/ion-exchange equilibrium between the aqueous sample and polymeric membrane. If concentration gradients in the contacting diffusion layers are insubstantial, the membrane response is thought to be rather independent of kinetic processes such as surface blocking effects. In this work, the surface of calcium-selective polymeric ion-selective electrodes is coated with polyelectrolyte multilayers as evidenced by zeta potential measurements, atomic force microscopy, and electrochemical impedance spectroscopy. Indeed, such multilayers have no effect on their potentiometric response if the membranes are formulated in a traditional manner, containing a lipophilic ion exchanger and a calcium-selective ionophore. However, drastic changes in the potential response are observed if the membranes are operated in a recently introduced kinetic mode using pulsed chronopotentiometry. The results suggest that the assembled nanostructured multilayers drastically alter the kinetics of ion transport to the sensing membrane, making use of the effect that polyelectrolyte multilayers have different permeabilities toward ions with different valences. The results have implications to the design of chemically selective ion sensors since surface-localized kinetic limitations can now be used as an additional dimension to tune the operational ion selectivity.     

An improved method for Organic Bound Tritium (OBT) determination in urine samples

The Organic Bound Tritium (OBT) amount in the body may induce changes in the evaluation of the internal exposure to tritium, due to its different retention time relative to HTO. OBT measurements for urine are not performed routinely, mainly because of the lengthy work needed in preparation of the samples, when using the standard oxygen combustion method. A simpler and more rapid method based on liquid scintillation counting (LSC) was employed, and an evaluation was performed to check its suitability for urine samples. The principle of the proposed method is based on subtracting the LSC counts of the water phase sample (HTO) from the total activity of the urine sample (OBT+HTO). A good correlation was found between the results obtained when applying the proposed direct method and the Gold standard method. The minimum detectable activity when using this method was determined.     

A comparative study of the adsorption of humic acid, fulvic acid and phenol onto Bacillus subtilis and activated sludge

The adsorption of humic acid and fulvic acid onto Bacillus subtilis cells and activated sludge biomass was studied as a function of pH and incubation time. The adsorption of humic and fulvic acids was strongly pH-dependent and followed the same trend on both surfaces, increasing in a sigmoidal way with decreasing pH over the 2-10 pH range. This behaviour is explained in terms of hydrophobic interactions between the uncharged biomass and the uncharged humic and fulvic acids. In contrast, the adsorption of phenol onto B. subtilis cells and activated sludge biomass showed in both cases an optimum pH at around 7.0. This optimum value may be interpreted in terms of a combination of hydrophobic interactions and hydrogen bonds between undissociated phenol and polar groups on the cell walls. Kinetic studies on the adsorption of humic acid, fulvic acid and phenol onto B. subtilis cells and sludge biomass pointed to a rapid uptake of the substances, with an equilibrium time of about 30 min. In all cases, the kinetic curves were acceptably fitted by non-linear regression to an exponential function, suggesting a first-order kinetic phenomenon. The specific adsorption values collected at optimum pH revealed that with the materials used in this work both B. subtilis and activated sludge follow the same adsorption trend: humic>fulvic>phenol. The lower adsorption of fulvic acid as compared with humic acid may be explained in terms of its lower hydrophobicity rather than its lower molecular size. On comparing the specific adsorption values of activated sludge versus B. subtilis, similar but lower figures were found for the three organic compounds studied. This similar behaviour suggests that both types of biomass base their adsorption capacity on the general characteristics of the bacterial cell wall, and the lower adsorption by the sludge would be due to a lower specific area due to clustering of the cells. This is remarkable, since sludge is a heterogeneous and cheap material in comparison with cultured bacterial cells.     

Ab initio correlation effects on the electronic and transport properties of metal(II)-phthalocyanine-based devices

Using first-principles calculations in the framework of density functional theory, we investigated the electronic and transport properties of metal(II)-phthalocyanine (M(II)Pc) systems, both in a single-molecule configuration and in a model device geometry. In particular, using copper(II)-Pc and manganese(II)-Pc as prototypical examples, we studied how electronic correlations on the central metal ion influence the analysis of the electronic structure of the system and we demonstrated that the choice of the exchange-correlation functional, also beyond the standard local or gradient corrected level, is of crucial importance for a correct interpretation of the data. Finally, our electronic transport simulations have shown that M(II)Pc-based devices can act selectively as molecular conductors, as in the case of copper, or as spin valves, as in the case of manganese, demonstrating once more the great potential of these systems for molecular nanoelectronics applications.     

Prediction of the Candida antarctica lipase A protein structure by comparative modeling and site-directed mutagenesis

A number of model structures of the CalA suggested by comparative modeling were tested by site-directed mutagenesis. Enzyme variants were created where amino acids predicted to play key roles for the lipase activity in the different models were replaced by an inert amino acid (alanine). The results from activity measurements of the overproduced and purified mutant enzymes indicate a structure where the active site consists of amino acid residues Ser184, His366, and Asp334 and in which there is no lid. This model can be used for future targeted modifications of the enzyme to obtain new substrate acceptance, better thermostability, and higher enantioselectivity.     

The ATP-binding site of protein kinase CK2 holds a positive electrostatic area and conserved water molecules

CK2 is a highly pleiotropic Ser/Thr protein kinase that is able to promote cell survival and enhance the tumour phenotype under specific circumstances. We have determined the crystal structure of three new complexes with tetrabromobenzimidazole derivatives that display K(i) values between 0.15 and 0.30 microM. A comparative analysis of these data with those of four other inhibitors of the same family revealed the presence of some highly conserved water molecules in the ATP-binding site. These waters reside near Lys68, in an area with a positive electrostatic potential that is able to attract and orient negatively charged ligands. The presence of this positive region and two unique bulky residues that are typical of CK2, Ile66 and Ile174, play a critical role in determining the ligand orientation and binding selectivity.     

Probe transit effect in interferometry of fast moving samples

When a fast moving transparent sample (with a speed close to c) is probed with a laser pulse, some artifacts can occur from data analysis. These artifacts are connected to the transit time of the probe through the sample and can mask the presence of a steep gradient of refractive index in the sample. We study this problem in the case of interferometry. In fact, the problem can affect the femtosecond interferometry of the media under ultrafast ionization by a propagating laser pulse. Two algorithms are introduced: the first based on the phase difference and the second based on visibility. Both algorithms allow for the reconstruction, under suitable assumptions, of an approximated refractive index profile from the distorted fringes.