A numerical experiment of backward erosion piping: kinematics and micromechanics

Meccanica - We report on a numerical experiment by which we investigated the propagation of an erosion pipe in a water saturated granular soil. The simulation was performed with a two-dimensional...     

Effect of the pulse trajectory on ultrasonic fluid velocity measurement

In a general situation a non-uniform velocity field gives rise to a shift of the otherwise straight acoustic pulse trajectory between the transmitter and receiver transducers of a sonic anemometer. The aim of this paper is to determine the effects of trajectory shifts on the velocity as measured by the sonic anemometer. This determination has been accomplished by developing a mathematical model of the measuring process carried out by sonic anemometers; a model which includes the non-straight trajectory effect. The problem is solved by small perturbation techniques, based on the relevant small parameter of the problem, the Mach number of the reference flow, M. As part of the solution, a general analytical expression for the deviations of the computed measured speed from the nominal speed has been obtained. The correction terms of both the transit time and of the measured speed are of M ² order in rotational velocity field. The method has been applied to three simple, paradigmatic flows: one-directional horizontal and vertical shear flows, and mixed with a uniform horizontal flow.     

The instability of an axially loaded viscoelastic constrained bar in the large displacement range

Summary This paper deals with the behaviour of an axially loaded viscoelastic structure at one degree of freedom in the large deformation range; the stress-strain relation assumed is linearly viscoelastic, with the kernel at non invariant memory, typical of concrete.The study is rigorously conducted for two types of restraint, characterizing, in the elastic range, the instability of both first and second kind; the problem is then stated in respect of a type of mixed restraint, such as can be found in some real structures, an approximate solution of which is here supplied.

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Sommario Vengono analizzate le caratteristiche di comportamento nel tempo di una struttura viscoelastica a un grado di libertà, caricata di punta, nel campo delle grandi deformazioni; il legame sforzi-deformazioni assunto è viscoelastico lineare, con il nucleo a memoria non invariante caratteristico dei calcestruzzi.Lo studio è svolto in forma rigorosa per due tipi di vincolo che caratterizzano, in campo elastico, l'instabilità di prima e quella di seconda specie; viene inoltre impostato il problema corrispondente ad un tipo di vincolo misto, presentato da alcune strutture reali, del quale si fornisce una soluzione approssimata.

     

Effects of mutational (Lys to Ala) surface charge changes on the redox properties of electrode-immobilized cytochrome c

Untrimethylated yeast iso-1-cytochrome c (cytc) and its single and multiple Lys to Ala variants at the surface lysines 72, 73, and 79 were adsorbed on carboxyalkanethiol self-assembled monolayers (SAMs) on gold, and the thermodynamics and kinetics of the heterogeneous protein-electrode electron-transfer (ET) reaction were determined by voltammetry. The reaction thermodynamics were also measured for the same species freely diffusing in solution. The selected lysine residues surround the heme group and contribute to the positively charged domain of cytc involved in the binding to redox partners and to carboxyl-terminated SAM-coated surfaces. The E degrees' (standard reduction potential) values for the proteins immobilized on SAMs made of 11-mercapto-1-undecanoic acid and 11-mercapto-1-undecanol on gold were found to be lower than those for the corresponding diffusing species owing to the stabilization of the ferric state by the negatively charged SAM. For the immobilized proteins, Lys to Ala substitution(s) do not affect the surface coverage, but induce significant changes in the E degrees' values, which do not simply follow the Coulomb law. The results suggest that the species-dependent orientation of the protein (and thereby of the heme group) toward the negatively charged SAM influences the electrostatic interaction and the resulting E degree' change. Moreover, these charge suppressions moderately affect the kinetics of the heterogeneous ET acting on the reorganization energy and the donor-acceptor distance. The kinetic data suggest that none of the studied lysines belong to the interfacial ET pathway.     

Theory, measurements, and modeling of OH and HO2 formation in the reaction of cyclohexyl radicals with O2

The production of OH and HO(2) in Cl-initiated oxidation of cyclohexane has been measured using pulsed-laser photolytic initiation and continuous-laser absorption detection. The experimental data are modeled by master equation calculations that employ new G2(MP2)-like ab initio characterizations of important stationary points on the cyclo-C(6)H(11)O(2) surface. These ab initio calculations are a substantial expansion on previously published characterizations, including explicit consideration of conformational changes (chair-boat, axial-equatorial) and torsional potentials. The rate constants for the decomposition and ring-opening of cyclohexyl radical are also computed with ab initio based transition state theory calculations. Comparison of kinetic simulations based on the master equation results with the present experimental data and with literature determinations of branching fractions suggests adjustment of several transition state energies below their ab initio values. Simulations with the adjusted values agree well with the body of experimental data. The results once again emphasize the importance of both direct and indirect components of the kinetics for the production of both HO(2) and OH in radical + O(2) reactions.     

Influence of the interface material layers and semiconductor energetic disorder on the open circuit voltage in polymer solar cells

Material layers at electrode/semiconductor interfaces are fundamental for the photovoltaic properties of polymer solar cells. The relationship between open‐circuit voltage ( V_OC ) and the work function ( φ ) of these interface layers is still a matter of debate. Simulations, together with experiments on over more than 20 cell architectures based on P3HT:PC₆₀BM, enabled us to analyze the physical dependence of V_OC on φ . In particular, when the work function of the contacts is well inside the gap we observe that performance depends strongly on even small variations of φ . On the other hand, when it approaches the energy levels of the semiconducting polymers, device operation becomes the most efficient and less sensitive to variations in φ . Furthermore, by varying the Gaussian density of states (DOS) of the active blend we were able to show that V_OC performance depends significantly also on the DOS. Our study based on the simultaneous variation of transport layers represents a promising method to optimize the design and performance of polymer solar cells. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 690–699