Tetramethyl guanidine-assisted synthesis and thermal crosslinking of multifunctional benzoxazine monomers based on natural phloretic acid

An efficient strategy to synthesize novel biobased multifunctional benzoxazine compounds was developed using the 1,1,3,3-tetramethyl guanidine (TMG)-triggered esterification of natural phloretic acid with organic halides as a key synthetic step. First, phloretic acid was combined with either aniline or furfurylamine to prepare the corresponding carboxylic acid-functional monobenzoxazine monomer. Next, the use of TMG enabled an efficient esterification of these compounds with di-, tri-, and tetra-functional benzyl bromide compounds at room temperature to afford a series of new multi-benzoxazine monomers tethered to an aromatic core. The effect of the functionality of the monomers on the curing process was analyzed, indicating that the reactivity during the thermally induced ring-opening increases with the number of furan and oxazine rings in the monomers. The resulting thermosets revealed good correlation between the number of oxazine rings in the structure of the monomer and the properties of the crosslinked materials. Furfurylamine-based polybenzoxazines showed improved thermal behavior compared to the aniline-based systems, due to the role of furan rings. All materials showed high T_g, good thermal stability, and promising flame retardancy properties.     

Internal symmetries of cellular automata

(Internal) transformations on the space Sigma of automaton configurations are defined as bi-infinite sequences of permutations of the cell symbols. A pair of transformations (gamma,theta) is said to be an internal symmetry of a cellular automaton f:Sigma-->Sigma if f=theta(-1)fgamma. It is shown that the full group of internal symmetries of an automaton f can be encoded as a group homomorphism F such that theta=F(gamma). The domain and image of the homomorphism F have, in general, infinite order and F is presented by a local automaton-like rule. Algorithms to compute the symmetry homomorphism F and to classify automata by their symmetries are presented. Examples on the types of dynamical implications of internal symmetries are discussed in detail. (c) 1997 American Institute of Physics.     

Nitric oxide binding and photodelivery based on ruthenium(II) complexes of 4-arylazo-3,5-dimethylpyrazole

Two fluorescent ligands, 3,5-dimethyl-4-(6'-sulfonylammonium-1'-azonaphthyl)pyrazole (dmpzn, 1) and 3,5-dimethyl-4-(4'-N,N'-dimethylaminoazophenyl)pyrazole (dmpza, 2) were obtained by condensation of ketoenolic derivatives with hydrazine. 1 and 2 formed the novel dinuclear complexes [(H(2)O)(3)ClRu(micro-L)(2)RuCl(H(2)O)(3)] (3 or 4) and [(H(2)O)(NO)Cl(2)Ru(micro-L)(2)RuCl(2)(NO)(H(2)O)] (6 or 7) (where L 1 = 2 or , respectively) which were characterized by IR, NMR and elemental analysis. The nitrosyl complexes were prepared by bubbling purified nitric oxide through methanol solutions of the corresponding ruthenium(II) chloroderivative or by reaction of the appropriate ligands with Ru(NO)Cl(3). Complexes 3 and 4 were found to bind NO, resulting in an increase in fluorescence. Ligand 1 also formed the mononuclear nitrosyl complex [Ru(NO)(bpy)(2)(dmpzn)]Cl(2) (8) which released NO in water at physiological pH and in the solid state as revealed by fluorescence and IR measurements, respectively.     

Using biased randomization for solving the two-dimensional loading vehicle routing problem with heterogeneous fleet

This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L-CVRP) with heterogeneous fleet (2L-HFVRP). The 2L-CVRP can be found in many real-life situations related to the transportation of voluminous items where two-dimensional packing restrictions have to be considered, e.g.: transportation of heavy machinery, forklifts, professional cleaning equipment, etc. Here, we also consider a heterogeneous fleet of vehicles, comprising units of different capacities, sizes and fixed/variable costs. Despite the fact that heterogeneous fleets are quite ubiquitous in real-life scenarios, there is a lack of publications in the literature discussing the 2L-HFVRP. In particular, to the best of our knowledge no previous work discusses the non-oriented 2L-HFVRP, in which items are allowed to be rotated during the truck-loading process. After describing and motivating the problem, a literature review on related work is performed. Then, a multi-start algorithm based on biased randomization of routing and packing heuristics is proposed. A set of computational experiments contribute to illustrate the scope of our approach, as well as to show its efficiency.     

Conformational adaptation and selective adatom capturing of tetrapyridyl-porphyrin molecules on a copper (111) surface

We present a combined low-temperature scanning tunneling microscopy and near-edge X-ray adsorption fine structure study on the interaction of tetrapyridyl-porphyrin (TPyP) molecules with a Cu(111) surface. A novel approach using data from complementary experimental techniques and charge density calculations allows us to determine the adsorption geometry of TPyP on Cu(111). The molecules are centered on "bridge" sites of the substrate lattice and exhibit a strong deformation involving a saddle-shaped macrocycle distortion as well as considerable rotation and tilting of the meso-substituents. We propose a bonding mechanism based on the pyridyl-surface interaction, which mediates the molecular deformation upon adsorption. Accordingly, a functionalization by pyridyl groups opens up pathways to control the anchoring of large organic molecules on metal surfaces and tune their conformational state. Furthermore, we demonstrate that the affinity of the terminal groups for metal centers permits the selective capture of individual iron atoms at low temperature.     

Preparation and Characterization of Carbon Nano‐Onion/PEDOT:PSS Composites

Composites of unmodified or oxidized carbon nano‐onions (CNOs/ox‐CNOs) with poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X‐ray photoelectron spectroscopy characterization is performed for pristine and ox‐CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox‐CNO/PEDOT:PSS composites.     

Time-dependent density-functional theory in massively parallel computer architectures: the OCTOPUS project

Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this paper we present the ongoing efforts to achieve the parallelization of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has great potential for execution in massively parallel systems such as modern supercomputers with thousands of processors and graphics processing units (GPUs). For harvesting the potential of conventional supercomputers, the main strategy is a multi-level parallelization scheme that combines the inherent scalability of real-time TDDFT with a real-space grid domain-partitioning approach. A scalable Poisson solver is critical for the efficiency of this scheme. For GPUs, we show how using blocks of Kohn-Sham states provides the required level of data parallelism and that this strategy is also applicable for code optimization on standard processors. Our results show that real-time TDDFT, as implemented in octopus, can be the method of choice for studying the excited states of large molecular systems in modern parallel architectures.     

Liebig–Denigès Method of Cyanide Determination: A Comparative Study of Two Approaches

The paper compares two approaches to the simulated argentometric titration of cyanide with the use of the modified Liebig?CDenigès (L-D) method, carried out according to GATES and applied with (1) classical and (2) pH-static titrations. Both approaches are discussed thoroughly and the results obtained from calculations are presented graphically. The calculations are performed with the use of an iterative computer program, based on charge and concentration balances and expressions for equilibrium constants, providing all physicochemical knowledge of the dynamic system in question. This way, physicochemical knowledge on complex electrolytic systems can be gained during the analytical procedure, i.e., the physicochemical and analytical knowledge are interrelated. The simulations follow the analytical procedures applied in experimental titrations and so provide an example of searching for the best a priori conditions for the quantitative analysis of cyanide. The computer program for pH-static titrations (described in this paper) enables one to carry out the simulation procedures with different preliminary data (concentrations, volumes).     

A Stopping Criterion for a Dynamic Competing Risks Model

We consider the development of a competing risks system following a two-stage stopping rule. This stopping procedure takes into account a desired probability of successfully completing an assigned task. Upon termination, the asymptotic properties of the estimator of the system reliability, as well as the stopping time variable, are examined. Moreover, the asymptotic risk associated with the two-stage procedure is presented. This risk is anchored on a loss function that considers losses incurred in not attaining the desired reliability and that of excessive testing.     

A Theoretical Perspective of the Photochemical Potential in the Spectral Performance of Photovoltaic Cells

We present a novel theoretical approach to the problem of light energy conversion in thermostated semiconductor junctions. Using the classical model of a two-level atom, we deduced formulas for the spectral response and the quantum efficiency in terms of the input photons’ non-zero chemical potential. We also calculated the spectral entropy production and the global efficiency parameter in the thermodynamic limit. The heat transferred to the thermostat results in a dissipative loss that appreciably controls the spectral quantities’ behavior and, therefore, the cell’s performance. The application of the obtained formulas to data extracted from photovoltaic cells enabled us to accurately interpolate experimental data for the spectral response and the quantum efficiency of cells based on Si-, GaAs, and CdTe, among others.