Bacteriostatic Behavior of PLA-BaTiO3 Composite Fibers Synthesized by Centrifugal Spinning and Subjected to Aging Test

The present work investigated the effect of Polylactic acid (PLA) fibers produced by centrifugal spinning with incorporated BaTiO₃ particles to improve their bacteriostatic behavior. The PLA matrix and three composites, presenting three different amounts of fillers, were subjected to UV/O₃ treatment monitoring the possible modifications that occurred over time. The morphological and physical properties of the surfaces were characterized by different microscopic techniques, contact angle, and surface potential measurements. Subsequently, the samples were tested in vitro with human dermal fibroblasts (HDF) to verify the cytotoxicity of the substrates. No significant differences between the PLA matrix and composites emerged; the high hydrophobicity of the fibers, derived by the polymer structure, represented an obstacle limiting the fibroblast attachment. Samples underwent bacterial exposure (Staphylococcus epidermidis) for 12 and 24 h. Increasing the concentration of BT, the number of living bacteria and their distribution decreased in comparison with the PLA matrix suggesting an effect of the inorganic filler, which generates a neutralization effect leading to reactive oxygen species (ROS) generation and subsequently to bacterial damages. These results suggest that the barium titanate (BT) fillers clearly improve the antibacterial properties of PLA fibers after aging tests made before bacterial exposure, representing a potential candidate in the creation of composites for medical applications.     

Detecting exponential dichotomy on the real line: SVD and QR algorithms

In this paper we propose and implement numerical methods to detect exponential dichotomy on the real line. Our algorithms are based on the singular value decomposition and the QR factorization of a fundamental matrix solution. The theoretical justification for our methods was laid down in the companion paper: “Exponential Dichotomy on the real line: SVD and QR methods.”     

Quantum cascade laser-based photoacoustic spectroscopy of volatile chemicals: application to hexamethyldisilazane

The use of photoacoustic spectroscopy and mid-infrared quantum-cascade lasers (QCLs) for the detection of hexamethyldisilazane (HMDS) is reported. A detection limit of 200 parts in 10(9) is found using a Fabry-Perot QCL operated at 8.4 microm in pulsed mode and a photoacoustic cell equipped with four electret microphones. The laser multimode spectrum matches the range of the N-H bending absorption band of HMDS. Further improvements to reach lower detection limits are discussed.     

Quadratic-Residue Codes and Cyclotomic Fields

We present an exposition of quadratic-residue codes through their embedding in codes over the quadratic subfield of the th cyclotomic field, the algebraic number field of th roots of unity. This representation allows the development of effective syndrome decoding algorithms that can fully exploit the code’s error-correcting capability. This is accomplished via Galois automorphisms of cyclotomic fields. For each fixed , the general results hold for all pairs , with a finite number of exceptions that depends on . A complete discussion of the set of quadratic-residue codes of length and dimension illustrates these results. This set includes the Golay code, the only perfect binary three-error-correcting code.A preliminary version of this paper was presented at the International Conference on Statistics, Combinatorics and Related Areas, October 3–5, 2003, University of Southern Maine, Portland, ME, USA.     

Counterpropagating spatial Kerr soliton in reflection gratings

We analytically predict the existence of both spatial bright and dark counterpropagating solitons in a reflection grating in the presence of the Kerr nonlinearity. The basic trapping mechanism consists of a twofold balance where diffraction is compensated by self-focusing and reflection is altered by the nonlinear-induced interferometric grating. We find that, whenever the spectral soliton profile lies within the grating stop band, bright and dark solitons exist only if the mutual phase of the counterpropagating solitons is pi or 0, respectively.     

Residual variance estimation using a nearest neighbor statistic

In this paper we consider the problem of estimating E[(Y−E[Y∣X])²] based on a finite sample of independent, but not necessarily identically distributed, random variables . We analyze the theoretical properties of a recently developed estimator. It is shown that the estimator has many theoretically interesting properties, while the practical implementation is simple.     

Synthesis of 4-haloserotonin derivatives and synthesis of the toad alkaloid dehydrobufotenine

4-Chloro-, 4-bromo- and 4-iodoserotonin derivatives were synthesized from 4-halo-5-oxyindoles, themselves derived from coumarins. Synthesis of the 4-iodoserotonins involved conjugate addition of an allyl group to a 5-iodocoumarin, followed by conversion of the allyl group into an aminoethyl unit. One of the iodoserotonin derivatives was converted into the toad alkaloid dehydrobufotenine, which was isolated as its hydroiodide.     

Volatile components of Centaurea bracteata and C. pannonica subsp. pannonica growing wild in Croatia

This paper reports on the volatile components of oils from the aerial parts (CBA) and roots (CBR) of Centaurea bracteata Scop. and aerial parts of C. pannonica (Heuffel) Simonkai subsp. pannonica (CPA), two Asteraceae growing wild in Croatia. The volatile components, obtained by hydrodistillation, were determined by GC-MS analysis. The yields (w/w) of the dried oils were 0.10% (CBA), 0.22% (CBR) and 0.09% (CPA), respectively. A total of 91 compounds were identified accounting for 91.1%, 93.3% and 87.9% of the total oil for CBA, CBR and CPA, respectively. All the samples were characterized mainly by hydrocarbons (7.1-34.1%), fatty acids (9.7-45.9%), and oxygenated sesquiterpenes (15.2-16.6%). The major components of the samples were hexadecanoic acid (8.1-31.1%), nonacosane (0.6-13.4%) and caryophyllene oxide (4.5-11.9%). Monoterpenes, both hydrocarbons and oxygenated, were either absent or present in low amounts in all the oils. The similarity in the oil contents is consistent with the two species being placed in the same section, Jacea.