Modification of a-Si under 100 eV Si atom bombardment

By molecular dynamics simulation, we study the response of an initially defect-free a-Si sample to 100 eV Si atom bombardment for fluences up to 2.6×10¹⁵ cm⁻², i.e., an equivalent of 4 ML coverage. Defects (over-coordinated atoms) are introduced into the sample at depths extending up to 30 Å, far beyond the average projectile range of 5.5 Å. This build-up of over-coordinated atoms is accompanied by a local increase of pressure of more than 1 GPa. For comparison, we also study atom bombardment of a strongly under-dense a-Si sample, prepared by simulated growth. This sample compactifies under irradiation, the initially high bulk concentration of under-coordinated atoms is reduced, and the initially tensile pressure in the sample relaxes.     

Do suspended sediments modulate the effects of octylphenol on rainbow trout?

A system was devised which allows particles to remain in suspension in a conventional 60 L aquarium without undue disturbance to resident fish. Using this system, juvenile rainbow trout were exposed for one week to 4-tert-octylphenol (OP, 10-1000 μg/L) with or without the presence of suspended sediments (10-20 mg/L of natural suspended sediments from the River Calder, UK). About 8% of the added OP partitioned to the solid phase. Vitellogenin levels were determined in the plasma of the exposed rainbow trout and showed a dose-dependent increase with regards to OP exposure concentration. Considerable variation in the vitellogenin response was observed between separate runs with the same OP concentration. There was no statistically significant (at P < 0.05) difference in plasma VTG levels between the OP treatments with or without suspended sediments. This suggests that the dissolved concentration is the key factor and natural suspended sediment neither protects against, nor exacerbates, the endocrine disrupting effect of OP on fish.     

Dynamical energy limits in traditional and work-driven operations II.: Systems with heat and mass transfer

This is the second part of the work that analyses dynamical energy limits for diverse operations with finite rates important in engineering. Our position is that a dynamic limit of a sufficiently high hierarchy may be helpful in modelling and design of a prescribed operation. In particular, we treat active systems with coupled heat and mass transfer important in separation and biological systems. The operations considered occur in separation units, heat and mass exchangers, energy converters and chemical reactors. The energy limits are expressed in terms of classical exergy and a residual minimum of entropy generated in equipment of a fixed dimension. To ensure physical limits we treat sequential work-driven operations, in particular those of dissolving or evaporation which run jointly with thermal machines (e.g. heat pumps). We also compare structures of optimization criteria describing these limits (in particular “endoreversible limits”) in traditional and work-driven operations. Through quantitative analyses we extend to the realm of mass transfer operations the method initiated in Part I that applies “Carnot variables” as suitable controls. Functions of extremum work, which apply a residual minimum entropy production, are found in terms of initial and final states, duration and (in discrete processes) number of stages. Mathematical analogies between entropy production expressions in traditional and work-driven operations are helpful to formulate optimization criteria in both cases.     

Investigation of oviposition deterrent in larval frass ofSpodoptera littoralis (Boisd.)

Previous experiments demonstrated an oviposition-deterring effect of larval frass in the Egyptian cotton leaf worm,Spodoptera littoralis (Boisd.). In this study, females were shown to perceive the oviposition-deterring substance(s) with their antennae. During dark, airtight, and cold (–10 °C) storage, the deterrent was persistent for at least 395 days. On the other hand, larval frass retained its activity for only two days when applied to cotton leaves. The deterrent activity of frass was independent of larval density. Frass of larvae reared at high densities deterred oviposition as well as frass of larvae feeding separately or in small groups. For significant oviposition deterrence, the minimum amount of frass was in the range of 5–10 mg frass per cotton leaf. An acetone extract of larval frass was highly deterrent, in contrast to extracts prepared with water, ethanol, chloroform, or pentane.     

Precipitation of titanium nitride in low-alloyed steel during solidification

The microsegregation of titanium and manganese and the precipitation of titanium nitride during dendritic solidification were investigated on an Fe-0.051%Ti-0.77%Mn alloy. Carbon and nitrogen were introduced into the liquid sample via the gas phase. The material solidifies as delta ferrite at a carbon mass content of about 0.08% but predominantly as austenite at ≥ 0.3%. At ferritic solidification, an about 3fold enrichment of the titanium in the residual melt between secondary dendrite arms is attained by segregration, whereas in the corners between some dendrites or grains in maximum a 10fold enrichment was detected. TiN particles of 0.5 to 1.0 μm size are formed only in the regions of maximum segregation where the supersaturation is higher than 15fold. An equal supersaturation has been calculated for homogeneous nucleation in the melt. The number of particles is moderate at 0.016% nitrogen but low at 0.008%. At austenitic solidification, the titanium content in the residual melt increases to more than the 30fold of the starting value. Particles formed in the melt grow to diameters in the 2 μm range.     

Surface chemistry of SnO2 nanowires on Ag-catalyst-covered Si substrate studied using XPS and TDS methods

In this paper we investigate the surface chemistry, including surface contaminations, of SnO₂ nanowires deposited on Ag-covered Si substrate by vapor phase deposition (VPD), thanks to x-ray photoelectron spectroscopy (XPS) in combination with thermal desorption spectroscopy (TDS). Air-exposed SnO₂ nanowires are slightly non-stoichiometric, and a huge amount of C contaminations is observed at their surface. After the thermal physical desorption (TPD) process, SnO₂ nanowires become almost stoichiometric without any surface C contaminations. This is probably related to the fact that C contaminations, as well as residual gases from air, are weakly bounded to the crystalline SnO₂ nanowires and can be easily removed from their surface. The obtained results gave us insight on the interpretation of the aging effect of SnO₂ nanowires that is of great importance for their potential application in the development of novel chemical nanosensor devices.     

A New Functional Form for Equations of State for Some Weakly Associating Fluids

A new functional form for equations of state for polar and weakly associating fluids was developed. It was established with a simultaneous optimization algorithm developed previously. As a result, equations of state in terms of the Helmholtz energy as a function of temperature and density were developed for hydrogen chloride (HCl) valid within \(T =\) (155–330) K and pressures up to \(p = 20\) MPa, diethyl ether (DEE) valid within \(T =\) (270–500) K and pressures up to \(p = 40\) MPa, and methyl chloride (R40) valid within \(T =\) (230–630) K and pressures up to \(p =\) 100 MPa. Those equations can be used for the calculation of all thermodynamic properties, including density, internal energy, enthalpy, heat capacity, speed of sound, saturation properties, etc.