Solvent extraction of hydrofluosilicic acid with alamine 336

Extraction constants for the solvent extraction of hydrofluosilicic acid with Alamine 336 have been determined. Two species were identified, (R₃NH⁺ )₂ SiF₆^2- and R₃NH⁺ HSiF₆, whose respective extraction constants were determined to be log K₂₁ = 7.42 and log K₁₁ = 2.60. For the dissociation of hydrofluosilicic acid the activity coefficient model presented by Bromley was adapted to sulphuric acid and the values used for hydrofluosilicic acid. The effect of the diluent was experimentally investigated.     

Investigation of the conditions for weld metal hydrogen cracking of low carbon offshore steels by the IRC weldability test

Three low carbon structural steels of different plate thickness have been investigated for hydrogen assisted cold cracking by the IRC weldability test at different restraint intensities. At diffusible hydrogen levels of 10–15 N ml/100 g Fe (ISO 3690), cracking decreases at increasing heat inputs due to a drop in restraint stress and hardness as well as an increase in hydrogen diffusion times. Critical heat inputs for crack prevention range from 0.95 to 1.4 kJmm^?1. Higher restraints enforce higher cracking stresses as well as final stresses of uncracked test welds. Higher restraints and lower heat inputs also induce faster stress increase during cooling which, for the steels containing Ni and Cu, shift the location of cracking from the HAZ to the weld metal. The steel without Ni and lower maximum HAZ hardness reveals weld metal cracking only, regardless of welding conditions. It can be concluded that for weld metal cracking, the relation between stress increase- and hydrogen effusion rates but also the relation between weld metal and HAZ microstructure and mechanical properties are responsible.     

Recent trends on the development of photobiological processes and photobioreactors for the improvement of hydrogen production

Hydrogen production through biological routes is promising because they are environmentally friendly. Hydrogen production through biophotolysis or photofermentation is usually a two stage process. In the first stage CO₂ is utilized for biomass production which is followed by hydrogen production in the second stage in anaerobic/sulfur-deprived conditions. In addition, one-stage photobiological hydrogen production process can be achieved using selected cyanobacterial strains. The major challenges confronting the large scale production of biomass/hydrogen are limited not only on the performance of the photobioreactors in which light penetration in dense cultures is a major bottleneck but also on the characteristics of the organisms. Other dependable factors include area/volume (A/V) ratio, mode of agitation, temperature and gas exchange. Photobioreactors of different geometries are reported for biohydrogen production: Tubular, Flat plate, Fermentor type etc. Every reactor has its own advantages and disadvantages. Airlift, helical tubular and flat plate reactors are found most suitable with respect to biomass production. These bioreactors may be employed for hydrogen production with necessary modifications to overcome the existing bottlenecks like gas hold up, oxygen toxicity and poor agitation. This review article attempts to focus on existing photobioreactors with respect to biomass generation and hydrogen production and the steps taken to improve its performance through engineering innovation that definitely help in the future design and construction of photobioreactors.     

An open-systems approach to calculating time-dependent spectra

Abstract

A new method to calculate the spectrum using cascaded open systems and a master equation is presented. The method uses two-state analyser atoms which are coupled to the system of interest, whose spectrum of radiation is read from the excitation of these analyser atoms. The ordinary definitions of a spectrum uses two-time averages and Fourier transforms. The present method uses only one-time averages. The method can be used to calculate time-dependent as well as stationary spectra.     

Client experience of psychodynamic psychotherapy for bulimia nervosa: An interview study.

We examined 14 bulimic clients' experiences of individual psychodynamic psychotherapy through semistructured interviews, which were analyzed using qualitative methods. The results showed that the psychodynamic approach was a challenge to most of the clients. Yet, most clients profited from therapy both symptomatically and with regard to interpersonal relations and affect regulation. There were, however, marked differences in the clients' experiences. One subgroup rather quickly felt that the therapy met their needs, another initially felt challenged by the approach and the therapeutic attitude but ultimately succeeded in using this particular kind of therapy. A third group remained predominantly critical of their therapies. The clinical implications and possible explanations of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Al-Cu-Zr和Al-Cu-Zr-Ti-V合金中Al_3Zr析出相的析出行为

利用透射电子显微技术研究Al-Cu-Zr和Al-Cu-Zr-Ti-V合金中Al3Zr的沉淀析出行为。亚稳态的Al3Zr沉淀相在枝晶中心均匀形核并获得均匀分布。然而,在枝晶边缘区域的析出复杂,观察到由许多球形Al3Zr析出颗粒组成的螺旋状和条状的形貌。条状的沉淀团簇沿100铝方向优先排列,这可能与Al2Cu的亚稳态θ′和稳态θ析出相相关。添加铜有利于Al3Zr沉淀相从L12→D023的结构转变。     

Solid-phase diffusion mechanism for GaAs nanowire growth

Controllable production of nanometre-sized structures is an important field of research, and synthesis of one-dimensional objects, such as nanowires, is a rapidly expanding area with numerous applications, for example, in electronics, photonics, biology and medicine. Nanoscale electronic devices created inside nanowires, such as p-n junctions, were reported ten years ago. More recently, hetero-structure devices with clear quantum-mechanical behaviour have been reported, for example the double-barrier resonant tunnelling diode and the single-electron transistor. The generally accepted theory of semiconductor nanowire growth is the vapour-liquid-solid (VLS) growth mechanism, based on growth from a liquid metal seed particle. In this letter we suggest the existence of a growth regime quite different from VLS. We show that this new growth regime is based on a solid-phase diffusion mechanism of a single component through a gold seed particle, as shown by in situ heating experiments of GaAs nanowires in a transmission electron microscope, and supported by highly resolved chemical analysis and finite element calculations of the mass transport and composition profiles.     

Development of a correlation between the non-polar solubility parameter,refractive index and molecular structure. II. Aliphatic ethers and alcohols

A relationship between the non-polar solubility parameter (λ) for polar aliphatic solvents and their refractive index has been developed. The use of structural group increments for branched isomers avoids the ambiguous choice between similarity in structure, reduced temperature and molal volume for the polar compound and its hydrocarbon homomorph. For straight-chain compounds, where a direct comparison with λ as calculated from a homomorph correlation function is possible, the mean discrepancy in λ is 0.07% for ethers and 0.14% for alcohols at 25°C.     

Global analysis of steady points for systems of differential equations with sigmoid interactions

A new method to investigate asymptotic properties of linear differential equations with strong threshold and switching effects is presented. The method is applied to systems of equations of the form dx/dt = F(x) - yx, where y = constant and the dependence of F on x is mediated by sigmoid functions. Using a special sigmoid function called a logoid, which rises monotonically from zero to one in a narrow interval surrounding the threshold value, exact analytical expressions for the limiting value of all steady points can be found in the limit when the logoid approaches a step function. The limiting values are independent of the shape of the logoid for a large class of logoids. Relations between steady points and limit cycles of the equations with logoids, their step function limit and the corresponding piecewise linear equations are derived. It is found that the approximation of sigmoids by the step function idealization is not always warranted. The results strongly suggest the use of logoids instead of other sigmoids hitherto employed