Partially acidulated phosphate rocks made from phosphoric acid using direct acidulation-granulation techniques

Partially acidulated phosphate rocks were produced by spraying phosphoric acid onto North Carolina phosphate rock of three finenesses (unground, medium, or finely ground) in a pan or drum granulator. This direct acidulation-granulation procedure resulted in free-flowing granular products using laboratory acid up to stoichiometric levels of 30% (unground), 45% (medium) and in excess of 50% (fine). However, when less pure works grade acids were used the maximum levels of acidulation were reduced to 15%, 30% and 45% respectively with a corresponding greater difficulty in producing good granules.Mature product analyses indicated an analytical bias with granule size, the larger granules containing greater quantities of soluble phosphate in most instances. Physical tests on mature products indicated that all granules produced were inferior to those of the traditional New Zealand fertiliser single superphosphate.     

Investigating the investigations: a retrospective study in the aviation maintenance error causation

In this paper, the impact of human reliability on aviation maintenance safety is investigated. Its purpose is to explore the actual mechanisms of maintenance errors initialization and propagation and hence to identify requisite characteristics for future solutions. Aviation maintenance errors account for between 12 and 15% of the global aviation accidents initiators, and this proportion rises to 23% when serious incidents are included. A wider global exercise of aviation maintenance safety improvement activities is consequently required. The current research applies the human error risk management in engineering systems (HERMES) methodology that conceptualizes two main streams of study: a retrospective investigation into human errors within aviation maintenance contexts, which is the main subject of this paper, and an ensuing prospective innovation of new tools that work to prevent future errors occurring. An extended fresh inquiry and a deeper data-mining process were concomitantly conducted. A new model signifying the initiation, accumulation, and propagation of crucial maintenance human errors within aviation maintenance organizations is thus introduced. Rotorcrafts are taken as a focal case study due to the high criticality naturally associated with their structural and operational characteristics.     

A streamline approach to two-dimensional steady non-ideal detonation: the straight streamline approximation

Detonations in non-ideal explosives tend to propagate significantly below the nominal one-dimensional detonation speed. In these cases, multi-dimensional effects within the reaction zone are important. A streamline-based approach to steady-state non-ideal detonation theory is developed. It is shown in this study that, given the streamline shapes, the two-dimensional problem reduces to an ordinary differential equation eigenvalue problem along each streamline, the solution of which determines the local shock shape that, in turn, leads to the solution of the detonation speed as a function of charge diameter. A simple approximation of straight but diverging streamlines is considered. The results of the approximate theory are compared with those of high-resolution direct numerical simulations of the problem. It is shown that the straight streamline approximation is remarkably predictive of highly non-ideal explosive diameter effects. It is even predictive of failure diameters. Given this predictive capability, one potential use of the method is in the determination of rate law parameters by fitting to data from unconfined rate stick experiments. This is illustrated by using data for ammonium nitrate fuel oil explosives.     

A critical analysis of the performance of molybdenum compounds in motor vehicles

The potential role of molybdenum-containing compounds in assisting energy conservation in transport systems is discussed. The importance of frictional losses in the major units of motor vehicles is assessed and the ability of molybdenum-containing compounds to reduce such losses in practice is illustrated.Improvements of 3% in engine efficiency and up to 4% in final drive efficiency are possible. Other frictional reductions in other drive line components are also possible as a result of using molybdenum-containing compounds.     

Time-resolved plasma characterisation of modulated pulsed power magnetron sputtering of chromium

Time-resolved Langmuir probe measurements have been employed to investigate the temporal development of the plasma properties, such as electron and ion density, electron temperature as well as the floating and plasma potential, during Modulated Pulsed Power Magnetron Sputtering (MPPMS). A chromium target was sputtered with an average power of 650 W in an argon atmosphere (0.53 Pa) employing two steps of excitation of the discharge which was realised by altering the modulation frequency of the voltage supplied to the target. The overall pulse duration was kept at 750 μs and a repetition frequency of 100 Hz was used. Three distinct stages of the discharge, namely the initial and the second step of excitation as well as the transition region which connects both stable states, were found. Maximum electron densities up to 7 × 10¹¹ cm^? 3 were obtained during the transient phase.     

Some factors associated with the use of the extractants 2% citric acid and 2% formic acid as estimators of available phosphorus in fertiliser products

The influences of calcium chloride, calcium sulphate, monocalcium phosphate, monosodium phosphate, calcium carbonate, sodium carbonate and iron and aluminium sulphates on the solubilities of two phosphate rocks (both ground and unground) in 2% citric and 2% formic acids have been examined. All of these potential impurity elements can affect the solubility of the phosphate rock through a variety of mechanisms, including common ion effects, complexation, acid-base reactions and reduction. 2% formic acid solubilities were slightly more influenced by these effects than 2% citric acid figures, militating against the use of this extractant for assessing mixed component products at present being manufactured in New Zealand.Solid to solvent and P to solvent ratios were also found to affect the solubilities of raw phosphate rocks and a correction for the differences in total P content of the phosphate rocks to produce a consistent P to solvent ratio in solubility tests is suggested. This study has indicated that alternative methods for assessing phosphate rocks in admixture with other components should be examined in future.     

Digital statistical analyser for low frequencies

A measurement process is described for the time integral of the square of a fluctuating voltage and the measuring time on two readout registers, leading to an instrument which provides first and second moments as well as the cumulative amplitude-probability distribution.     

The use of chemical solubility tests in comparing phosphate fertilisers

The standard solubility tests as used in New Zealand for assessing single superphosphate have been applied to alternative high analysis fertilisers such as triple superphosphate and partially acidulated phosphate rocks using phosphoric acid. Under differing experimental conditions it has been established that the phosphate rock component has a variable solubility in 2% citric acid at all levels, and in neutral ammonium citrate at high levels of PR content, making comparisons between percentages of soluble P derived from different fertilisers inappropriate for chemical or agronomic assessment. Only water, which extracts all the monocalcium phosphate component but none of the phosphate rock, can be used to compare the efficiency of the acidulation process, and neutral ammonium citrate can be used to assess the amount of phosphate rock remaining when the acidulation level is in excess of 50%. 2% formic acid produced almost identical results to 2% citric acid for partially acidulated materials and therefore cannot be recommended as an alternative, improved extractant for fertilisers containing large proportions of residual phosphate rock.     

The impact of alerting designs on air traffic controller’s eye movement patterns and situation awareness

Abstract

This research investigated controller’ situation awareness by comparing COOPANS’s acoustic alerts with newly designed semantic alerts. The results demonstrate that ATCOs’ visual scan patterns had significant differences between acoustic and semantic designs. ATCOs established different eye movement patterns on fixations number, fixation duration and saccade velocity. Effective decision support systems require human-centered design with effective stimuli to direct ATCO’s attention to critical events. It is necessary to provide ATCOs with specific alerting information to reflect the nature of the critical situation in order to minimise the side effects of startle and inattentional deafness. Consequently, the design of a semantic alert can significantly reduce ATCOs’ response time, therefore providing valuable extra time in a time-limited situation to formulate and execute resolution strategies in critical air safety events. The findings of this research indicate that the context-specified design of semantic alerts could improve ATCO’s situational awareness and significantly reduce response time in the event of Short Term Conflict Alert (STCA) activation which alerts to two aircraft having less than the required lateral or vertical separation.

Practitioner Summary: Eye movements are closely linked with visual attention and can be analysed to explore shifting attention whilst performing monitoring tasks. This research has found that context-specific designed semantic alerts facilitated improved ATCO cognitive processing by integrating visual and auditory resources. Semantic designs have been demonstrated to be superior to acoustic design by directing the operator’s attention more quickly to critical situations.Abbreviations: APW: area proximity warning; ASRS: aviation safety reporting system; ATC: air traffic control; ATCO: air traffic controller; ATM: air traffic management; COOPANS: cooperation between air navigation service providers; HCI: human-computer interaction; IAA: irish aviation authority; MSAW: minimum safe altitude warning; MTCD: medium-term conflict detection; SA: situation awareness; STCA: short term conflict alert; TP: trajectory prediction     

Adaptation of a Digitally Predistorted RF Amplifier Using Selective Sampling

In this paper,a reduced-cost method of measuring residual nonlinearities in an adaptive digitally predistorted amplifier is proposed.Measurements obtained by selective sampling of the amplifier output are integrated over the input envelope range to adapt a fourth-order polynomial predistorter with memory correction.Results for a WCDMA input with a 101 carrier configuration show that a transmitter using the proposed method can meet the adjacent channel leakage ratio(ACLR) specification.Inverse modeling of the nonlinearity is proposed as a future extension that will reduce the cost of the system further.