An Interferometric Optical Technique for In-Situ Measurement of Fiber Diameter

The diameter distribution of fibers plays an important role in the performance of many fiberglass products. The fiberglass industry, however, currently lacks the advanced instrumentation necessary for performing on-line fiber diameter measurements. Enhanced measurement capabilities would provide manufacturers and researchers a tool to improve fiberizing methods, production efficiency, and overall fiberglass product performance. This paper describes the size measurement of moving glass fibers using the Phase Doppler Anemometry technique. Simulation results are presented and validated experimentally. Theoretical modeling uses the mathematical solution for a tilted circular cylinder interacting with focused Laser beams. Experimental laboratory studies have been also conducted to evaluate the factors not included in the theoretical models.     

Elements with prime and small indices in bicyclic biquadratic number fields

We give necessary and sufficient conditions for the existence of primitive algebraic integers with index A in totally complex bicyclic biquadratic number fields where A is an odd prime or a positive rational integer at most 10. We also determine all these elements and prove that there are infinitely many totally complex bicyclic biquadratic number fields containing elements with index A.     

Understanding the mechanism of the intramolecular stetter reaction. A DFT study

The mechanism of the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction of salicylaldehyde 1 to yield chromanone 3 has been theoretically studied at the B3LYP/6-31G** level. This NHC-catalyzed reaction takes place through six elementary steps, which involve: (i) formation of the Breslow intermediate IN2; (ii) an intramolecular Michael-Type addition in IN2 to form the new C-C s bond; and (iii) extrusion of the NHC catalyst from the Michael adduct to yield chromanone 3. Analysis of the relative free energies in toluene indicates that while formation of Breslow intermediate IN2 involves the rate-determining step of the catalytic process, the intramolecular Michael-type addition is the stereoselectivity determining step responsible for the configuration of the stereogenic carbon a to the carbonyl of chromanone 3. An ELF analysis at TSs and intermediates involved in the Michael-type addition allows for the characterization of the electronic changes along the C-C bond-formation.     

Structural and thermal properties of spray-dried methotrexate-loaded biodegradable microparticles

Drug–polymer interactions, structural properties, thermal behavior, and stability of biodegradable microparticles are fundamental aspects in the developing of new polymeric drug delivery systems. In this study, poly (d,l-lactide-co-glycolide) (PLGA) microparticles containing methotrexate (MTX) were successfully obtained by spray drying. Scanning electronic microscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and drug-loading efficiency were used to investigate the effect of drug–polymer ratio and its interactions, in a new MTX-loaded PLGA spray-dried microparticles. High levels of encapsulation efficiency (about 90 %) and a prevalent spherical shape were identified for different drug–polymer ratios used (9, 18, and 27 % m/m). The thermal analyses (DSC and TG) and XRD indicate that MTX is homogeneously distributed in the polymeric matrix, with a prevalent amorphous state in a stable molecular dispersion. Therefore, a correlation between drug content and the structural-thermal properties of drug-loaded PLGA microparticles was established using the thermal analysis data. The biodegradable microparticle leads to an increment of thermal stability of MTX, confirming that spray drying is an efficient process for obtaining MTX-loaded PLGA microparticles.     

”Direct” causal cascade in the stock market

We use wavelets to decompose the volatility (standard deviation) of intraday (S&P500) return data across scales. We show that when investigating two-point correlation functions of the volatility logarithms across different time scales, one reveals the existence of a causal information cascade from large scales (i.e. small frequencies) to fine scales. We quantify and visualize the information flux across scales. We provide a possible interpretation of our findings in terms of market dynamics. Received: 9 January 1998 / Received in final form and accepted: 13 January 1998     

Hydrinden-Derivate. V

Ohne Zusammenfassung     

Comprehensive two-dimensional gas chromatography with capillary flow modulation to separate FAME isomers

A method to separate FAME and the linoleic and linolenic acids isomers by GCxGC using an apparatus equipped with a capillary flow technology (CFT) based modulator and a FID detector has been developed. Four different column combinations (one conventional and three inverted phase sets) were used in these experiments. The conventional set first involved a DB5-MS non-polar column followed by a highly polar HP-INNOWax column in the second dimension. The inverted phase set comprised of a highly polar BPX-70 column in the first dimension and a non-polar ZB5-MS column for the second dimension. Furthermore, the influence of the length of the second dimension column on FAME isomer separation was studied in the inverted phase sets, along with other parameters like the modulation time and column flow. The best results in terms of the time required for the analysis and number of FAME identified with the inverted set were achieved with the shorter second dimension column. After supercritical fluid extraction, the method was applied to identify FAMEs in broccoli leaves from three different cultivars (Naxos, Nubia and Viola).     

Cooperative effects at water-crystalline silica interfaces strengthen surface silanol hydrogen bonding. An ab initio molecular dynamics study

Silica and silica based materials are widely used in chemistry and materials science due to their importance in many technological fields. The properties of these materials, which are crucial for their applications, are mainly determined by the presence of hydrogen bonding between surface silanols. Here, we present ab initio molecular dynamics simulations (AIMD) on different surfaces derived from the crystallographic α-quartz (100) and the α-cristobalite (001) and (101) faces, both free and at the interface with liquid water. The focus was on studying whether water adsorption can disrupt the H-bond pattern at the pristine free silica surface and how deep the perturbation due to the contact with the surface affects the structure of the water multilayer. Results highlight that the water phase is over structured at the interface with silica, as compared to water bulk. Furthermore, an apparent counterintuitive behavior has been observed for quartz (100) and cristobalite (001) surfaces: the interaction with water does not cleave the pre-existent H-bonds between the surface silanol groups. On the contrary, in several cases, it is observed that SiOH···OHSi H-bonds are even strengthened, as the result of a mutual cooperative H-donor/H-acceptor enhancement between silanols and water molecules, which may alter the adsorption capability of these silica surfaces.     

DFT study of the fragmentation mechanism of uracil RNA base

The fragmentation process of the uracil RNA base has been investigated via DFT calculations in order to assign fragments to the ionisation mass spectrum obtained after dissociation induced by collision experiments. The analysis of the electronic distribution and geometry parameters of the cation allows selection of several bonds that may be cleaved and lead to the formation of various fragments. Differences are observed in the electronic behaviour of the bond breaking as well as the energy required for the cleavage. It is reported that N(3)-C(4) and N(1)-C(2) bonds are more easily cleaved than the C(5)-C(6) bond, since the corresponding energy barriers amount to ΔG = +1.627, +1.710, +5.459 eV, respectively, which makes the C(5)-C(6) bond cleavage almost prohibited. Among all possible formed fragments, the formation of the OCN(+) fragment for the peak at m/z = 42 Da is excluded because of an intermediate that was not observed experimentally and too a large free energy barrier. Based on the required free energy, it is observed that two fragment derivatives: C(2)H(4)N(+) and C(2)H(2)O˙(+) may be formed, with a small preference for C(2)H(4)N(+). This latter product is not formed through a retro Diels Alder reaction in contrast to C(2)H(2)O˙(+). The following sequence is proposed for the peak at 42 Da: C(2)H(4)N(+) (from N(1)-C(2), C(4)-C(5) cleavages) > C(2)H(2)O˙(+) (from N(3)-C(4), N(1)-C(2) and C(5)-C(6) cleavages) > C(2)H(4)N(+) (from N(1)-C(2), N(3)-C(4) and C(4)-C(5)) > C(2)H(2)O˙(+) (from C(5)-C(6), N(1)-C(2) and N(3)-C(4) cleavages) > NCO(+) (from N(1)-C(2), C(4)-C(5) and N(3)-C(4) cleavages). Finally the peak at 28 Da is assigned to CNH(2)(+) derivatives that can be formed through two different paths, the easiest one requiring 5.4 eV.