Two Dieneplatinum Synthetic Reagents,Pt(C6H2F3‐2,4,6)2(cod) and Pt(C6HF4‐2,3,4,5)2(cod)

Reactions of PtCl₂(cod) (cod = cycloocta‐1,5‐diene) with 2,4,6‐trifluoro‐ and 2,3,4,5‐tetrafluoro‐phenyllithium in diethyl ether gives Pt(C₆H₂F₃‐2,4,6)₂(cod) ( 1 ) (monoclinic, P2₁/n, Z = 4, a = 7.141(1), b = 15.002(2), c = 17.071(3) Å, β = 91.37(2)°) and Pt(C₆HF₄‐2,3,4,5)₂(cod) ( 2 ) (triclinic, P 1, Z = 2, a = 10.150(2), b = 10.762(2), c = 10.812(2) Å, α = 63.606(3), β = 63.327(3), γ = 76.496(3)°) respectively, which have two ipso carbon atoms and two double bond midpoint centres in a square planar arrangement, and aromatic rings angled near perpendicular to the coordination plane.     

Crossed product of cyclic groups

All crossed products of two cyclic groups are explicitly described using generators and relations. A necessary and sufficient condition for an extension of a group by a group to be a cyclic group is given.     

General Lower Bounds for the Minor Crossing Number of Graphs

There are three general lower bound techniques for the crossing numbers of graphs: the Crossing Lemma, the bisection method and the embedding method. In this contribution, we present their adaptations to the minor crossing number. Using the adapted bounds, we improve on the known bounds on the minor crossing number of hypercubes. We also point out relations of the minor crossing number to string graphs and establish a lower bound for the standard crossing number in terms of Randič index.     

On spectral characterizations and embeddings of graphs

The least eigenvalue of the 0-1 adjacency matrix of a graph is denoted λ G. In this paper all graphs with λ(G) greater than ?2 are characterized. Such a graph is a generalized line graph of the form L(T;1,0,…,0), L(T), L(H), where T is a tree and H is unicyclic with an odd cycle, or is one of 573 graphs that arise from the root system E₈. If G is regular with λ(G)>?2, then Gis a clique or an odd circuit. These characterizations are used for embedding problems; λ_R(H) = sup{λ(G)z.sfnc;HinG; Gregular}. H is an odd circuit, a path, or a complete graph iff λ_R(H)> ?2. For any other line graph H, λ_R(H) = ?2. A similar result holds for complete multipartite graphs.     

Method of preparing stable composites of a Cu-aluminosilicate microporous compound and cellulose material and their characterisation

A new aluminosilicate cellulose composite material was prepared by coating hydrogel on a cotton fabric. An aluminosilicate material zeolite Faujasite (FAU) was synthesised for a series of desired properties, observing the possibilities of the isomorphous replacement of Al or/and Si atoms, within the structure, with copper. Aluminosilicate microporous material was prepared by convection hydrothermal synthesis, applying microwave energy. The selection and modification of the zeolite deposition procedures on the cellulose material was also carried out. The stability of the obtained cellulose material to washing was determined. The crystalline structure of the aluminosilicate samples and their composites with cellulose materials were checked employing X-ray diffraction analysis. The following analysis methods were used for physicochemical characterisation: Fourier transform infrared spectroscopy and field emission scanning electron microscope with EDS. Structural properties of the newly created composite materials were investigated using the following standard methods: surface mass according to ISO 3801:1977, determination of thickness according to ISO 5084:1996, tensile strength according to DIN EN ISO 13934-1 and air permeability according to HRN EN ISO 9237:2003. Completely new constructional properties, compared to the unprocessed cellulose material, of the newly formed composite materials are mainly evident from the following experimental results: the air permeability values decrease for both samples (59.87 and 61.76 % for Cel-AlSi 1_K and Cel-AlSi 1_M, respectively), the areal density change values (1.45 % for Cel-AlSi 1_K, 4.61 % for Cel-AlSi 1_M), the sample thickness increased by 21.55 % for both composite materials while the tensile strengths decrease slightly for both samples (5.83 % for Cel- AlSi 1_K, 6.41 % for Cel-AlSi 1_M).     

Ethanol Production from Cashew Apple Bagasse: Improvement of Enzymatic Hydrolysis by Microwave-Assisted Alkali Pretreatment

In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses, and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L⁻¹ of NaOH (372 ± 12 and 355 ± 37 mg g_glucan⁻¹) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step, improvement on solid percentage (16% w/v) and enzyme load (30 FPU g_CAB-M⁻¹) increased glucose concentration to 15 g L⁻¹. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L⁻¹ and 1.41 g L⁻¹ h⁻¹, respectively.     

High-gain harmonic-generation free-electron laser seeded by harmonics generated in gas

The injection of a seed in a free-electron laser (FEL) amplifier reduces the saturation length and improves the longitudinal coherence. A cascaded FEL, operating in the high-gain harmonic-generation regime, allows us to extend the beneficial effects of the seed to shorter wavelengths. We report on the first operation of a high-gain harmonic-generation free-electron laser, seeded with harmonics generated in gas. The third harmonics of a Ti:sapphire laser, generated in a gas cell, has been amplified and up-converted to its second harmonic (λ(rad)=133 nm) in a FEL cascaded configuration based on a variable number of modulators and radiators. We studied the transition between coherent harmonic generation and superradiant regime, optimizing the laser performances with respect to the number of modulators and radiators.     

Electroless plating of nickel–phosphorous on surface-modified poly(ethylene terephthalate) films

Chemical surface preparation for Ni–P electroless metallization of poly(ethylene terephthalate) (PET) films without using Chromium-based chemicals, was studied. The applicability of this method was verified by a subsequent metallization process. Thermal analysis was conducted to observe the main thermal transitions and stability of the polymer and metallized films. Contact angle analysis was performed to assess the surface hydrophilicity so as to optimize the substrate preparation process. X-ray diffraction, EDAX and SEM analysis were used to understand the composition and morphology of the polymeric substrate and Ni–P coat growing process. Adherence strength, contact sheet resistivity and optical diffuse reflection were measured on the metallized films. The time of chemical etching affects the polymer surface hydrophilicity, polymer/metal adherence strength, surface resistance and optical diffuse reflection, while Ni coating morphology is controlled by the pH of the electroless bath. High wettability of the polymer surface, adherence strength of 800 N cm⁻², high optical diffuse reflection and low surface resistivity of the Ni coating, were found for films etched for 60 min. Metallizations performed at pH 7.5 produce Ni–P coatings with 12.0 wt.% phosphorous content, which were amorphous and flexible. The contact sheet resistivity of the plated films is sensitive to roughness variations of the substrate. The method proposed in this work allows the production of metallized films appropriate for the fabrication of flexible circuits.     

The circular chromatic number of a digraph

We introduce the circular chromatic number χ_c of a digraph and establish various basic results. They show that the coloring theory for digraphs is similar to the coloring theory for undirected graphs when independent sets of vertices are replaced by acyclic sets. Since the directed k‐cycle has circular chromatic number k/(k – 1), for k ≥ 2, values of χ_c between 1 and 2 are possible. We show that in fact, χ_c takes on all rational values greater than 1. Furthermore, there exist digraphs of arbitrarily large digirth and circular chromatic number. It is NP‐complete to decide if a given digraph has χ_c at most 2. © 2004 Wiley Periodicals, Inc. J Graph Theory 46: 227–240, 2004     

On Lagrange’s History of Mechanics

The birth of Lagranges Mechanics constitutes a milestone in the history of Mechanics. The genius of Lagrange should have been aware of this turning point inasmuch as he devoted a substantial part of his celebrated book to an account of the previous development of Mechanics. This historical part, located before the technical exposition in the Mécanique analytique, is the subject of the present paper. By directly consulting the original writings of the scientists that contributed to the development of Mechanics, Lagrange produced a first hand historical account. It largely influenced the historians of the XIX century and also those of the beginning of XX century. We interpret Lagranges motivations for writing his history and we suggest an interpretation of the foundations of his historical account.