Evaluation of gas chromatographic isotope fractionation and process contamination by carbon in compound-specific radiocarbon analysis

The relevance of both modern and fossil carbon contamination as well as isotope fractionation during preparative gas chromatography for compound-specific radiocarbon analysis (CSRA) was evaluated. Two independent laboratories investigated the influence of modern carbon contamination in the sample cleanup procedure and preparative capillary gas chromatography (pcGC) of a radiocarbon-dead 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) reference. The isolated samples were analyzed for their 14C/12C ratio by accelerator mass spectrometry. Sample Delta14C values of -996 +/- 20 and -985 +/- 20 per thousand agreed with a Delta14C of -995 +/- 20 per thousand for the unprocessed PCB 169, suggesting that no significant contamination by nonfossil carbon was introduced during the sample preparation process at either laboratory. A reference compound containing a modern 14C/12C ratio (vanillin) was employed to evaluate process contamination from fossil C. No negative bias due to fossil C was observed (sample Delta14C value of 165 +/- 20 per thousand agreed with Delta14C of 155 +/- 12 per thousand for the unprocessed vanillin). The extent of isotopic fractionation that can be induced during pcGC was evaluated by partially collecting the vanillin model compound of modern 14C/12C abundance. A significant change in the delta13C and delta14C values was observed when only parts of the eluting peak were collected (delta13C values ranged from -15.75 to -49.91 per thousand and delta14C values from -82.4 to +4.71 per thousand). Delta14C values, which are normalized to a delta13C of -25 per thousand, did not deviate significantly (-58.9 to -5.8 per thousand, considering the uncertainty of approximately +/-20 per thousand). This means that normalization of radiocarbon results to a delta13C of -25 per thousand, normally performed to remove effects of environmental isotope fractionation on 14C-based age determinations, also cor-rects sufficiently for putative isotopic fractionation that may occur during pcGC isolation of individual compounds for CSRA.     

Review on the Oxidation of Metallic Thermal Sprayed Coatings: A Case Study with Reference to Rare-Earth Permanent Magnetic Coatings

Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices. Despite this potential, thermal spray of PMCs is still not widely explored due to oxidation concerns. It was established that oxidation leads to the loss of ferromagnetic phases in these materials and results in deterioration of magnetic performance. Although this review focuses on a specific class of material, i.e., magnetic materials, there is significant technical crossover to all classes of feedstocks that are employed in thermal spray processing. The oxidation mechanisms and the associated influencing factors are explored in this work to implement effective processing techniques during the deposition process. This paper reviews the various stages and mechanisms of oxidation in thermal spray processes. The factors that influence the extent of oxidation depend on the type of oxidation that is dominant and rely on the type of spray system, powder injection position, and the particle size of feedstock. Among the aspects that are reviewed include the oxygen-fuel ratio for high velocity oxygen-fuel (HVOF), current intensity, gas flow rate, particle size, spray distance, and substrate temperature. Protection strategies to minimize oxidation in thermal spray processes, such as gas shrouding and shielding, are presented.     

Void Formation and Spatial Distribution in Plasma Sprayed Nd-Fe-B Coatings

Formation of voids is inevitable in plasma sprayed coatings and the role of voids on coating properties has long been established. In fact, the void content within coatings is adjusted by optimizing the process parameters to obtain coatings with desirable performance. Quantification of voids via image analysis allows determination of not only the void content within a coating, but also the spatial distribution of the voids. Void content in plasma sprayed neodymium iron boron (Nd-Fe-B) coatings was adjusted by changing the standoff distance, and was found to vary from 1.8 to 8.2%. Spatial distribution parameters, which include nearest neighbor distance (d _min), mean near neighbor distance (d _mean), and nearest neighbor angle (θ_n), were determined via the Dirichlet tessellation method. Coefficient of variation (COV) values of d _min and d _mean allow determination of inhomogeneity and degree of clustering of the voids within a coating. The θ_n values reveal the anisotropic behavior of voids within plasma sprayed coatings. The influence of void content and its spatial distribution within the coatings on the microhardness and elastic modulus of coatings was determined.     

A mixed isogeometric analysis and control volume approach for heat transfer analysis of nonuniformly heated plates

Abstract

A framework for conducting heat transfer analysis of nonuniformly heated plates using isogeometric analysis (IGA) is proposed. The modeling approach represents a method that is capable of capturing the full 3D thermal states of plate structures subjected to nonuniform heating. The formulation can be deemed a mixed IGA and control-volume scheme that describes the governing equations using a set of 2D lumped temperature layers. The non-matching grids between the fire domain and the solid domain are weakly coupled. Numerical results demonstrate that the approach is a suitable first step towards coupled CFD-IGA-based fire-structure simulation.     

The predictive value of behavioural characteristics on the success of strategic alliances

An increasing number of companies are setting up strategic alliances with suppliers and customers. However, the majority of these alliances do not succeed. Our aim is to understand how different behavioural characteristics are associated with alliance success. We hypothesise that alliance attributes, communication behaviour, and alliance management are predictors of cost benefits and service benefits. Furthermore, we found that while alliance attributes are related with both cost and service benefits, communication behaviour and alliance management are only associated with service and cost benefits, respectively. We also see that alliance attributes explain most of the variance of supply chain success and are thus better predictors of alliance success than other behavioural characteristics. Furthermore, we provide insight into the way managers can build up supply chain performance by setting up strategic alliances.     

Optimal linear phase mask for the singular beam synthesis from a Gaussian beam and the scheme of its experimental realisation

The functions of phase wedge and symmetric phase mask for optical vortex synthesised from a Gaussian beam are carefully analysed. The optimal linear phase dependence in the cross-section of a Gaussian beam for the singular beam with a single charge synthesis is found. The similarity of the obtained beam phase and intensity distributions in the singular beam depending on the distance of the resulting field observation is investigated. The simple original technique of the experimental realisation of the necessary phase mask for the singular beam synthesis with the help of two inclined mirrors is offered.     

无线充电应用的次级端整流桥应用方案研究

本文主要介绍了在无线充电应用中,如何进行次级端的整流桥设计,并对三种设计方案进行了比较,得出采用2颗肖特基二极管和2颗MOSFET的最佳最佳整流桥配置方案。     

Al/Cu键合系统中金属间化合物的形成规律及防止方法

Al/Cu键合界面金属间化合物的形成是导致微电子器件失效的重要因素之一,总结了微电子器件生产和使用过程中Al/Cu键合界面金属间化合物的生长规律,分析了Al/Cu键合系统的失效机制。热超声键合过程中,Al焊盘上氧化铝层的破裂使金属间化合物的形成成为可能,键合及器件使用过程中,金属间化合物和柯肯德尔空洞的形成和长大最终导致键合失效。采用在Al焊盘上镀覆Ti过渡层的方法,可有效降低键合系统中Cu原子的扩散速度,抑制金属间化合物的生长,从而提高电子元器件的可靠性。     

Chemical and biological recovery of Lake Saudlandsvatn, a formerly highly acidified lake in southernmost Norway, in response to decreased acid deposition

We studied acid-sensitive organisms in Lake Saudlandsvatn in southernmost Norway in relation to acidification: brown trout (Salmo trutta), the caddisfly Hydropsyche siltalai and the zooplankter Daphnia longispina. The study lake was highly acidified with episodic pH depressions <5.0 in the 1970s and 1980s, and sulphur (S) deposition five times greater than the critical load. Chemical recovery following reduced deposition of S became evident in the late 1990s, when the pH increased to 5.5-6.0. By 2000, S deposition had decreased to the critical load. The lake sustained a good brown trout population until the early 1980s, but then it started to decline and nearly went extinct ten years later. Severe recruitment failures were found in most years prior to 1995, both in the inlet and outlet stream. However, since 2003 a marked recovery of the brown trout population has occurred in the lake. During the 1980s, the H. siltalai disappeared from the lake tributaries. In 1996, the species reappeared, and increased highly in abundance from 2000 and onwards. The first post-acidification record of D. longispina from net hauls in Lake Saudlandsvatn was in 2002. Palaeolimnological data confirmed their presence prior to acidification. Any significant recovery in all three organism groups coincided with an acid-neutralizing capacity (ANC) of > 20 μeq L^− 1 and toxic inorganic aluminium of < 30 μg L^− 1. Projections made with the MAGIC model indicate that unless further reductions in deposition of S are made, the ANC will fluctuate around the ANC survival threshold for the biological elements described. Thus, full biological recovery will not occur in the near future.