McEliece Public Key Cryptosystems Using Algebraic-Geometric Codes

McEliece proposed a public-key cryptosystem based on algebraic codes, in particular binary classical Goppa codes. Actually, his scheme needs only a class of codes with a good decoding algorithm and with a huge number of inequivalent members with given parameters. In the present paper we look at various aspects of McEliece's scheme using the new and much larger class of R-ary algebraic-geometric Goppa codes.     

Viscoelastic relaxation mechanisms of conventional polypropylene toughened by a plastomer

Plastomers are new alternatives that provide a higher impact strength in polypropylene synthesized by conventional methods. This study presents an analysis of the structure and thermal characterization of two sets of polypropylene/plastomer blends. The difference between the two polypropylene samples is their molecular weight. With the structural knowledge obtained, a comprehensive analysis of the different relaxation processes has been performed. Neither component is miscible. The area under the loss tangent curves provides preliminary information about how the toughness is enhanced with this type of impact modifier. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1878–1888, 2003     

Periodic,incommensurate and chaotic states in a continuum statistical mechanics model

We study the thermodynamic behavior of a continuum system with competing periodicities. We show that in addition to commensurate and incommensurate phases, there exist configurations which are chaotic in nature and exhibit no long-range order. These phases are metastable and characterized by an order parameter with a continuous spectrum. By transforming the problem of determining the ground states of the system into a classical mechanics problem, we construct a two-dimensional area-preserving map which can be used to study the qualitative nature of the orbits. Our results might be of relevance to adsorbed monolayers on periodic substrates.     

LC-Multistage Mass Spectrometry for the Characterization of Poly(Butylene Adipate-co-Butylene Terephthalate) Copolyester

A comprehensive study using liquid chromatography electrospray ionization multistage mass spectrometry (LC-ESI MS ⁿ ) was performed to get detailed structural information on poly(butylene adipate-co-butylene terephthalate) co-polyester and its product of partial degradation. LC-MS and LC-MSⁿ identified the existence of cyclic structures in the original samples that disappear completely during the degradation. The occurrence of methanol transesterification in the degradation process was confirmed. MS² on the first ¹³C isotope peak helped to determine the elemental composition of the fragments and facilitated end group determination. The method can be used to provide an alternative for high mass accuracy MS² experiments. Sequence information was also revealed for certain copolymeric structures.     

Infrared spectroscopy of Li(+)(CH4)1Ar(n), n = 1-6, clusters

Infrared predissociation (IRPD) spectra of Li(+)(CH(4))(1)Ar(n), n = 1-6, clusters are reported in the C-H stretching region from 2800 to 3100 cm(-1). The Li(+) electric field perturbs CH(4) lifting its tetrahedral symmetry and gives rise to multiple IR active modes. The observed bands arise from the totally symmetric vibrational mode, v(1), and the triple degenerate vibrational mode, v(3). Each band is shifted to lower frequency relative to the unperturbed CH(4) values. As the number of argon atoms is increased, the C-H red shift becomes less pronounced until the bands are essentially unchanged from n = 5 to n = 6. For n = 6, additional vibrational features were observed which suggested the presence of an additional conformer. By monitoring different photodissociation loss channels (loss of three Ar or loss of CH(4)), one conformer was uniquely associated with the CH(4) loss channel, with two bands at 2914 and 3017 cm(-1), values nearly identical to the neutral CH(4) gas-phase v(1) and v(3) frequencies. With supporting ab initio calculations, the two conformers were identified, both with a first solvent shell size of six. The major conformer had CH(4) in the first shell, while the conformer exclusively present in the CH(4) loss channel had six argons in the first shell and CH(4) in the second shell. This conformer is +11.89 kJ/mol higher in energy than the minimum energy conformer at the MP2/aug-cc-pVDZ level. B3LYP/6-31+G* level vibrational frequencies and MP2/aug-cc-pVDZ level single-point binding energies, D(e) (kJ/mol), are reported to support the interpretation of the experimental data.     

Thioether-phosphite: new ligands for the highly enantioselective Ir-catalyzed hydrogenation of minimally functionalized olefins

We have described the first successful application of non-N-donor heterodonor ligands--thioether-phosphite ligands--in the Ir-catalyzed hydrogenation of minimally functionalized olefins. Excellent enantioselectivities (ee's up to 99%) have been obtained for a range of substrates, including challenging terminal disubstituted substrates, under standard conditions.     

Structural, thermal and optical characterization of a Schiff base as a new organic material for nonlinear optical crystals and films with reversible noncentrosymmetry

Macroscopic single crystals of (E)-5-(diethylamino)-2-((3,5-dinitrophenylimino)methyl)phenol (DNP) were obtained from slow cooling of chloroform or dichlorometane saturated solutions at controlled temperature. X-ray diffraction analysis showed that this compound crystallizes in a noncentrosymmetric space group (P2(1)2(1)2(1)). Thermal analysis was performed and indicated that the crystals are stable until 260 °C. Second-order nonlinear optical properties of DNP were experimentally investigated in solution through EFISH technique and in solid state through the Kurtz-Perry powder technique. Crystals of compound DNP exhibited a second-harmonic signals 39 times larger than of the technologically useful potassium dihydrogenphosphate (KDP) under excitation at infrared wavelengths. In addition, the second-order nonlinear optical properties of DNP were also studied at visible wavelengths through the photorefractive effect and applied to demonstrate dynamic holographic reconstruction.     

A comparative study of physical and chemical processes for removal of biomass in biofilters

After 6 months of operation a long-term biofilter was stopped for two weeks and then it was started up again for a second experimental period of almost 1.3 years, with high toluene loads and submitted to several physical and chemical treatments in order to remove excess biomass that could affect the reactor's performance due to clogging, whose main effect is a high pressure drop. Elimination capacity and removal efficiency were determined after each treatment. The methods applied were: filling with water and draining, backwashing, and air sparging. Different flows and temperatures (20, 30, 45 and 60 °C) were applied, either with distilled water or with different chemicals in aqueous solutions. Treatments with chemicals caused a decrease of the biofilter performance, requiring periods of 1 to 2 weeks to recover previous values. The results indicate that air sparging with pure distilled water as well as with solutions of NaOH (0.01% w/v) and NaOCl (0.01% w/v) were the treatments that removed more biomass, working either at 20, 30 or 45 °C and at relatively low flow rates (below 320 L h(-1)), but with a high biodegradation inhibition after the treatments. Dry biomass (g VS) content was determined at three different heights of the biofilter in order to carry out each experiment under the same conditions. The same amount of dry biomass when applying a treatment was established so it could be considered that the biofilm conditions were identical. Wet biomass was used as a control of the biofilter's water content during treatments. Several batch assays were performed to support and quantify the observed inhibitory effects of the different chemicals and temperatures applied.     

Pyrrolic tripodal receptors for carbohydrates. Role of functional groups and binding geometry on carbohydrate recognition

The contribution from several H-bonding groups and the impact of geometric requirements on the binding ability of benzene-based tripodal receptors toward carbohydrates have been investigated by measuring the affinity of a set of structures toward octyl β-D-glucopyranoside, selected as a representative monosaccharide. The results reported in the present study demonstrate that a judicious choice of correct geometry and appropriate functional groups is critical to achieve the complementary hydrogen bonding interactions required for an effective carbohydrate recognition.     

New seven membered palladacycles: C-Br bond activation of 2-bromo-pyridine derivative by Pd(II)

C-Br bond activation followed by a C-C coupling reaction of the 2-bromo-pyridyl unit of [1-phenyl-2-(6-bromopyridin-2-yl)-benzoimidazole] was performed by Pd(CH(2)CMe(2)-o-C(6)H(4))(η(4)-COD). Two new seven membered palladacycles were obtained. A combined experimental and theoretical DFT study elucidates the mechanism for this reaction.