Search results

This paper aims to introduce a series of experimental results which are the extension of our previous novel observations (Xie et al., Soft Matter, 2011), which could be helpful for revealing the lubrication failure mechanism in bearings when they are exposed to an electrical environment.

An experimental apparatus where a ball was in contact with a glass disk coated with a semi-reflective chromium layer. A small volume of oil droplet was put into the microgap of the ball-disk contact. Then, a potential was applied onto the oil micropool formed by the droplet surrounding the contact region.

It has been found that destabilization of the low-conducting oil micropool around the contact region could be induced after applying a potential. Thin oil films could be drained out of the oil pool and spread on the tribopair surfaces, resulting in the depletion of the oil pool. When the applied potential was increased, the occurrence of spreading would be easier and its development would be more obvious. In contrast, the electrospreading behavior would be suppressed when the oil viscosity, contact load and oil pool size were increased. Thermocapillary force due to thermal effect as a result of the current flow near the oil pool border has been proposed as the main driving force for the spreading behavior. The influences of the operating parameters have been ascribed to the change of the electric current near the oil pool border as well as the corresponding variations in the temperature rise and the surface tension of the oil pool.

This is the first study to directly observe that the lubricant oil micropool around the contact region could deplete after applying a potential, potentially resulting in oil starvation in the contact region.

The purpose of this study is to reveal the underlying mechanism in film formation of oil-in-water (O/W) emulsion.

This study focuses on the film forming characteristics of O/W emulsion between the surface of a steel ball and a glass disc coated with chromium. The lubricant film thicknesses of O/W emulsion with various mechanical stirring strength were discussed, which were observed by technique of relative optical interference intensity.

The authors directly observed the oil pool in the contact area, finding the size of oil pool was closely related to the film-forming ability of emulsion. Enrichment phenomenon occurs in oil pool, which was caused by phase inversion. Further investigations revealed that the emulsion is stable with strong stirring strength, resulting in a smaller oil pool size and worse film forming ability.

With the wide usage of O/W emulsion in both biological and industrial systems, the ability of emulsion film formation is considered as an important factor to evaluate the lubrication effectiveness.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0354/

This paper aims to establish a prediction model of stable transmission time of spiral bevel gear during a loss-of-lubrication event in helicopter transmission system.

To observe the temperature change of spiral bevel gear during working condition, a test rig of spiral bevel gear was developed according to the requirements of experiments and carried out verification experiments.

The prediction is verified by the test of detecting the temperature of oil pool. The main damage form of helicopter spiral bevel gears under starved lubrication is tooth surface burn. The stable running time under oil-free lubrication is mainly determined by the degree of tooth surface burn control.

The experimental data of the spiral bevel gear oil-free lubrication process are basically consistent with the simulation prediction results. The results lay a foundation for the working life design of spiral bevel gear in helicopter transmission system under starved lubrication.

The purpose of this paper is to identify and characterize a geological storage site at more than 800 m depth that is capable of storing large quantities of carbon dioxide (CO₂) in the Alberta Basin and is close to a large CO₂ supply.

Five criteria are used to select the site: total volume of the pore space of the formation for CO₂ (i.e. capacity); accessibility of the pore space in the storage site to CO₂ (i.e. permeability or injectivity); ability of the storage site to retain the CO₂ once the CO₂ has been injected (i.e. containment); protection of other resources from contamination; and cost of the whole process: capture of the CO₂, transport and storage (i.e. economics).

The Heartland Redwater Leduc Reef is identified as a site that has large capacity, good injectivity, and is an excellent trap. Contamination of the oil in the oil reservoir at the top of the reef (the third largest oil reservoir in Canada) is avoided by co‐optimizing CO₂ storage and oil production.

The Heartland Redwater Leduc Reef is ideally located at relatively shallow depth (1,000‐1,200 m), has a large amount of residual oil and is close to large CO₂ sources which make it one of the most economically attractive sites in the Western Canadian Sedimentary Basin.

The Heartland Redwater Leduc Reef Saline Aquifer CO₂ Capture and Geological Storage Project (HARP) is investigating the technical and economic feasibility of injecting significant volumes of CO₂ into the large water‐saturated portion of a huge Devonian reef that is capped by a comparatively small oil reservoir, nevertheless the third largest oil pool in Canada. The reef has a total areal extent of nearly 600 km³, is more than 1,000 m deep and is up to 275 m thick. Based on the high‐water injectivity in the reef, the potential exists to inject sustainably in excess of 1,000 tonnes of CO₂ per day per well in the aquifer portion of the reef. Preliminary storage capacity estimates for the aquifer are in the order of one gigatonne of CO₂. The Heartland Redwater Leduc Reef has the combination of a large oil reservoir sitting on top of a much larger local aquifer. This is a unique site for storage in Canada and could be a model for the rest of the world for carbon dioxide capture and storage.

Purpose – This chapter examines the licensing behavior of patent pools when they are unconstrained by antitrust rules.

Design/methodology/approach – Patent pools allow competing firms to combine their patents and license them as a package to outside firms. Regulators today favor pools that license their patents freely to outside firms, making it difficult to observe the unconstrained licensing strategies of patent pools. This chapter takes advantage of a unique period of regulatory tolerance during the New Deal to investigate the unconstrained licensing decisions of pools. Archival evidence suggests that – in the absence of regulation – pools may not choose to license their technologies.

Findings/originality/value – Eleven of twenty pools that formed between 1930 and 1938 did not issue any licenses to outside firms. Three pools granted one, two, and three licenses, respectively, to resolve litigation. Six pools issued between 9 and 185 licenses. Archival evidence suggests that the pools studied in this chapter used licensing as a means to limit competition with substitute technologies.

This study aims to investigate the contingent roles real effective exchange rates (REERs) play in mediating the effects of oil revenue on the agriculture sector value-added in 25 major and minor oil-exporting (MIOEC) countries during the period of 1975–2014.

The panel autoregressive distributed lag (ARDL) estimator proposed by Pesaran et al. (1999) was relied upon to achieve the objectives of the study. This estimator involves a pool of small cross-sectional units over a long-time span that covers for 25 oil-exporting countries over 39 years (1975–2014).

This paper reveals the following findings. Firstly, oil revenue has a direct negative effect on agricultural value-added in the short- and long-term. This finding holds for full sample and subsamples of major oil-exporting (MAOEC) and MIOEC countries. Further assessment reveals that the magnitude of the impact is larger for MAOEC than that of the MIOEC. Secondly, the finding for the long-run effect shows that the contingent effect of real exchange rate on the nexus between oil revenue and agricultural value-added is negative and statistically significant at the conventional level for the full sample. This suggests that, in the long-run, the appreciation in real exchange rates exacerbate the negative marginal effects of oil revenue on agricultural value-added in all oil-exporting countries. However, when sub-samples of MAOEC and MIOEC are considered, the contingent effect disappeared (become insignificant) in MAOEC while it is positive and statistically significant in MIOEC. Thus, in the long-run, the appreciation in real exchange rates diminishes the negative marginal effects of oil revenue on agricultural value-added in MIOEC. While oil revenue has a direct negative effect, its effect is also moderated by the variations in REERs in MIOEC in the long-run. Finally, in the short-run, fluctuations in the real exchange rate do not matter for the nexus of oil revenue and agriculture sector in these countries whether minor or MAOEC countries.

This study contributes to the debate in the empirical literature on the Dutch disease effect and “oil curse”. Using the appropriate panel ARDL empirical framework, it provides evidence on how exchange rate variations in the oil-exporting countries influence the nature of the effects of the oil revenue on agricultural sectors in the long-run but not in the short-run. Contingent effects of REERs only appear to exist in MIOEC in the long-run.

The cleaning of food production equipment using cleaning detergents may contaminate the lubricant of the bearings, thereby reducing the bearing service life. The purpose of this paper is to investigate the cause and mechanism of such damage of bearings lubricated by cleaning detergent/water-in-oil emulsions.

The emulsion was prepared by adding a mixture of cleaning detergent and water in one base oil. A self-designed ball-on-disc optical interference test rig was applied to examine the effect of emulsion on lubrication and wear of bearing contacts under pure sliding conditions.

The emulsion reduced lubricating film thickness at a relatively low-sliding speed but only when the water concentration (20%) in emulsion was high. Water droplets were trapped around the ball-on-disc contact area under static conditions because of a high capillary force. The emulsion can induce damages on the soft surface in the startup mainly due to the presence of water around the contact.

The basic lubrication behaviour of water/oil emulsions containing cleaning detergent under pure sliding was experimental studied and the mechanism of bearing damage in food production equipment was investigated. Based on the study, the solution to avoid such damage was proposed.

This paper aims to explore the extreme effect of crude oil price fluctuations and its volatility on the economic growth of Middle East and North Africa (MENA) countries. It also investigates the asymmetric and dynamic relationship between oil price and economic growth. Further, a separate analysis for each MENA oil-export and oil-import countries is conducted. Furthermore, it studies to what extent the quality of institutions will change the effect of oil price fluctuations on economic growth.

As the effect of oil price fluctuations is not the same over different business cycles or oil price levels, the paper uses a panel quantile regression approach with other linear models such as fixed effects, random effects and panel generalized method of moments. The panel quantile methodology is an extension of traditional linear models and it has the advantage of exploring the relationship over the different quantiles of the whole distribution.

The paper can summarize results as following: changes in oil price and its volatility have an opposite effect for each oil-export and oil-import countries; for the former, changes in oil prices have a positive impact but the volatility a negative effect. While for the latter, changes in oil prices have a negative effect but volatility a positive effect. Further, the impact of oil price changes and their uncertainty are different across different quantiles. Furthermore, there is evidence about the asymmetric effect of the oil price changes on economic growth. Finally, accounting for institutional quality led to a reduction in the impact of oil price changes on economic growth.

The study concludes more detailed results on the impact of oil prices on gross domestic product growth. Thus, it can be used as a decision-support tool for policymakers.

The purpose of this paper is to examine and compare the impact of oil and gas prices shocks on the non-performing loans (NPLs) of banks at the aggregate as well as at the level of commercial and Islamic banks in Qatar over the period 2000-2016.

Using the West Texas Intermediate Database, BankScope Database, World Bank’s World Development Indicators Database, and International Monetary Fund Database, the authors use a one-step system generalized method of moments dynamic model to examine and compare the association between oil and gas prices shocks with NPLs in Qatari banks. The authors also test the hypotheses of direct and indirect impacts of oil price shocks and gas price shocks on bank NPLs.

The results indicate that oil price shocks and gas price shocks do not have directly affect NPLs of Qatari banks at the aggregate level, while they have indirect effects that are channeled through the country-specific macroeconomic and institutional factors. The authors find that oil and gas prices shocks affect NPLs of Qatari Islamic banks directly through extended oil and gas-related cash flows, while their impact on the NPLs of Qatari commercial banks is indirect. In other words, Islamic banks in Qatar greatly benefits from increased cash flow caused by the rise in the oil and gas prices, which make their NPLs, much lower than that in commercial banks. Better capital cushion, better managerial efficiency, better risk management, and liquidity management systems should be used by the Islamic banks in Qatar to expand their customer base. The authors also find that positive fiscal stance of the government reduces the NPLs in both commercial and Islamic banks.

The results of this study necessitate policy measures that can counter the effects of changes in oil and gas prices on the growth of bank NPLs.

It is widely recognized that oil and gas prices and the level of production are of great importance to the economic development of oil and gas-exporting countries. So far, however, no econometric study has been reported in the literature which analyses and compares the impact of oil and gas prices shocks on the NPLs of commercial and Islamic banks and also at the aggregate level in any of the oil economies. Thus, this study provides the first empirical evidence on distinct direct and indirect channels through which oil and gas prices shocks may affect bank NPLs.