Thermodynamic properties of equilibrium air by an exact two-equation model for Euler and Navier–Stokes CFD algorithms

This paper details an exact two-equation procedure to generate pressure, temperature and mass and mole fractions as well as their thermodynamic and Jacobian partial derivatives for five-species neutral equilibrium air. Applicable for arbitrary forms of equilibrium constants and especially designed for explicit and implicit CFD algorithms, the procedure algebraically reduces to two equations the six-equation thermodynamic system comprising the equations for internal energy, law of mass action and conservation of species mass and ratio of oxygen and nitrogen nuclei. This exact algebraic reduction explicitly expresses four mass fractions in terms of nitric oxide mass fraction and temperature, which are then determined through a rapidly converging numerical solution of the internal energy and nitric oxide mass action equations. The procedure then exactly determines the partial derivatives of pressure, temperature and mass fractions analytically. The mathematical formulation also introduces a convenient system non-dimensionalization that makes the procedure uniformly applicable to flows ranging from shock tube flows with zero initial velocity to aerothermodynamic flows with supersonic/hypersonic freestream Mach numbers. Over a wide range of density and internal energy the predicted distributions of mole fractions for the model five species agree with independent published results, while pressure and temperature as well as their partial derivatives remain continuous, smooth and physically meaningful. © 1997 John Wiley & Sons, Ltd.     

Segmented liquid crystalline polyesters with allyl group as lateral substituent

The synthesis and a partial characterization of segmented liquid crystalline polymers with 3,3′-diallyl-4,4′-dihydroxybiphenyl unit in the rigid moiety is reported. The general formula of polymers is [-p-C₆H₄-COO-p-C₆H₃(R)-p-C₆H₃(R)-OOC-p-C₆H₄-O-(CH₂)_nO-]_x, with n = 6, 8, 10, 12, and R =  CH₂ CHCH₂. All polymers have nematic liquid-crystalline behavior. At room temperature, annealed fiber samples of polymers show a complex polymorphism. Three phases have been isolated with very large unit cells accommodating 6 or 12 chains. The projection of the molecular packing in a plane perpendicular to the c axis is characterized by the organization of chains in a two-dimensional hexagonal or quasi-hexagonal array. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2371–2378, 1998     

DNA Damage Induced by Late Spring Sunlight in Antarctica

Sunlight ultraviolet (UV) radiation constitutes an important environmental genotoxic agent that organisms are exposed to, as it can damage DNA directly, generating pyrimidine dimers, and indirectly, generating oxidized bases and single-strand breaks (SSBs). These lesions can lead to mutations, triggering skin and eye disorders, including carcinogenesis and photoaging. Stratospheric ozone layer depletion, particularly in the Antarctic continent, predicts an uncertain scenario of UV incidence on the Earth in the next decades. This research evaluates the DNA damage caused by environmental exposure to late spring sunlight in the Antarctic Peninsula, where the ozone layer hole is more pronounced. These experiments were performed at the Brazilian Comandante Ferraz Antarctic Station, at King’s George Island, South Shetlands Islands. For comparison, tropical regions were also analyzed. Samples of plasmid DNA were exposed to sunlight. Cyclobutane pyrimidine dimers (CPDs), oxidized base damage and SSBs were detected using specific enzymes. In addition, an immunological approach was used to detect CPDs. The results reveal high levels of DNA damage induced by exposure under the Antarctic sunlight, inversely correlated with ozone layer thickness, confirming the high impact of ozone layer depletion on the DNA damaging action of sunlight in Antarctica.     

On the effect of model uncertainty on the Hopf bifurcation of aeroelastic systems

Nonlinear Dynamics - Nowadays, humanity is facing one of the most dangerous pandemics known as COVID-19. Due to its high inter-person contagiousness, COVID-19 is rapidly spreading across the world....     

Crosslinking of a fibrous sample to a macro-oriented mesomorphic network

Preliminary results on the synthesis and characterization of anisotropic networks, oriented on a macroscopic scale, are reported. Fiber samples of segmented thermotropic liquid-crystalline polymers bearing the oxypentenyl lateral substituent have been crosslinked via thermally activated radical reaction. This was made possible by immersion of fiber samples in dichloromethane containing t-butylperoxybenzoate as activating agent, thus allowing its diffusion in the samples. Subsequent annealing at 145°C brings us to an anisotropic network with no loss of the original orientation. A mesophase is stabilized and no structural modification is observed by heating samples from room temperature up to 400°C, where thermal decomposition takes place. Crosslinked fibers exhibit good tensile properties, at both room temperature and at 150°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 433–438, 1998     

Influence of the Temperature on the Crystal Structure of Poly(p‐phenylene sulfide): A Study by X‐Ray Measurements and Molecular Mechanics

The crystal structure of poly(p‐phenylene sulfide) (PPS) has been investigated by X‐ray analysis on fiber samples and by molecular mechanics calculations over a wide range of temperatures, from 0 K to 548 K, showing that all the structural parameters remain substantially constant. The thermal expansion coefficients of the a and b axes have been evaluated. Structural parameters experimentally obtained at the various temperatures have been used in calculations by molecular mechanics. The crystal structures calculated by various methods and using several potential functions are in very good agreement. New parameters are proposed for the nonbonded terms of the potential functions.     

Characterization of the aeolian aerosol from Cape Verde by k 0-INAA and PIXE

Due to its location on West Coast of Africa, Cape Verde is highly influenced by Sahara Desert dust events being an optimum place to observe and study the African aeolian aerosol. During 2011, particulate matter with an aerodynamic diameter lower than 10 μm (PM₁₀) was sampled in Santiago Island and its chemical composition was evaluated by k ₀-instrumental neutron activation analysis (k ₀-INAA) and particle induced X-ray emission (PIXE). This study showed the existence of a seasonal intrusion of dust from Africa (that occurred from October to March) characterized by significant increases of PM₁₀, mineral elements and anthropogenic particles concentrations. In 2011, the PM₁₀ health-based air quality guidelines defined by WHO, EU and USEPA were exceeded. Cape Verde PM₁₀ composition was characterized essentially by high concentrations of elements originating from the soil (Ca, Ce, Co, Fe, K, Mg, Mn, Rb, S, Sc, Si, Sm, and Ti) and sea (Br, Cl, and Na); and low concentrations of anthropogenic elements (As, Cr, Cu, Ni, Pb, Sb, V, and Zn). k ₀-INAA and PIXE were fundamental tools for the determination of airborne chemical elements in Cape Verde. Their multi-elemental capabilities in association with low detection limits made it possible to determine the majority of the element concentrations of environmental interest.     

Plasma processing of the Si(0 0 1) surface for tuning SPR of Au/Si-based plasmonic nanostructures

Au nanoclusters have been deposited on Si(0 0 1) surfaces by sputtering of a metallic Au target using an Ar plasma. Different wet and dry treatments of the Si(0 0 1) surface, including dipping in HF solution and exposure to H₂ and N₂ plasmas, have been applied and the effects of these treatments on the Au nanoparticles/Si interface, the Au nanoclusters aspect ratio and the surface plasmon resonance (SPR) energy and amplitude are investigated exploiting spectroscopic ellipsometry and atomic force microscopy. It is found that the Au nanoclusters aspect ratio depends on the extent of the Au-Si intermixing. The thicker the Au-Si interface layer, the larger the Au nanoparticles aspect ratio and the red-shift of the SPR peak. Furthermore, SiO₂ and the H₂ plasma treatment inhibit the Si-Au intermixing, while HF-dipping and the N₂ plasma treatment favour Au-Si intermixing, yielding silicide formation which increases the Si wetting by Au.