Shielding Gas Coaxial Jet Pipes Numerical Study of a Vertical Laser Welding Process of AZ91 Magnesium Alloy

The laser welding of magnesium alloys, largely used in many fabrication applications, has gained considerable interest especially in aerospace, electronics, automotive industry etc. Unfortunately, this process is associated to an undesired phenomenon which is “oxidation”. For this reason, a good shielding system of the welding zone is of major importance. This paper presents a numerical study using computational fluid dynamics (CFD) of a laser welding process employing a moving volumetric heat source. Starting with the turbulence model validity, a parametric study of this welding process in a vertical position aiming to optimize the design of protection gas device, the gas jet inclination, the appropriate welding direction and the gas type is, then, proposed. The optimum parametric combination ensuring the largest gas coverage area is the one where the shielding gas is Argon, supplied by the coaxial nozzles at a downward inclination angle with respect to the laser beam axis, and a downward welding direction

Elevated atmospheric CO2 concentration ameliorates effects of NaCl salinity on photosynthesis and leaf structure of Aster tripolium L.

This study investigated the interaction of NaCl-salinity and elevated atmospheric CO2 concentration on gas exchange, leaf pigment composition, and leaf ultrastructure of the potential cash crop halophyte Aster tripolium. The plants were irrigated with five different salinity levels (0, 25, 50, 75, 100% seawater salinity) under ambient and elevated (520 ppm) CO2. Under saline conditions (ambient CO2) stomatal and mesophyll resistance increased, leading to a significant decrease in photosynthesis and water use efficiency (WUE) and to an increase in oxidative stress. The latter was indicated by dilations of the thylakoid membranes and an increase in superoxide dismutase (SOD) activity. Oxidative stress could be counteracted by thicker epidermal cell walls of the leaves, a thicker cuticle, a reduced chlorophyll content, an increase in the chlorophyll a/b ratio and a transient decline of the photosynthetic efficiency. Elevated CO2 led to a significant increase in photosynthesis and WUE. The improved water and energy supply was used to increase the investment in mechanisms reducing water loss and oxidative stress (thicker cell walls and cuticles, a higher chlorophyll and carotenoid content, higher SOD activity), resulting in more intact thylakoids. As these mechanisms can improve survival under salinity, A. tripolium seems to be a promising cash crop halophyte which can help in desalinizing and reclaiming degraded land

Food Security as a Public Good: Oman’s Prospects

The recent phenomenal crisis in the financial sector and the surge in food prices have resurrected the debate on the role of government, in economic management and in particular in securing national food security. This paper briefly reviews the theoretical literature in favor of government intervention in the market to secure food security. It is argued that food security needs to be considered as a public good, hence justifying government intervention in supplying it. Sustaining the potential to domestically produce safe minimum amounts of a staple food should be considered as a national strategic objective to achieve food security. Wheat is a staple food in Oman and it has been a major crop in the farming systems of Oman. Wheat cultivation under present circumstances of crop prices, yield, agricultural technology and resource availability in Oman’s commercial farming is not viable, without government support. With the use of a linear programming model that simulates the farming systems; in a major agricultural region in Oman (Batinah region) the production subsidy that is required as an incentive to promote the cultivation of wheat is estimated. The wheat yield in Oman is considered as 3 Tons/Ha and world price of wheat is around 100 OR/Ton. Wheat cultivation under commercial farming would be viable if a subsidy of at least 414 OR/Ha (138 OR/Ton) is provided. This subsidy can be instrumented as an input subsidy and/or price supports as Saudi Arabia had done (190 OR/Ton of wheat). If the wheat yield could be increased through technological and managerial means to global potential yield of 5 Tons/Ha then the price support needs to be at least 83 OR/Ton of wheat. The extent of its achievement in terms of extent of land cultivated and total domestic production of wheat, need to be considered in relation to the trade-off of fiscal cost and political choice of the degree of food security deemed as necessary to achieve

Internationalization of Oman Fisheries Firms After the European Union Ban

This paper examines the impacts of the l998 ban on Oman fish exports to the EU markets and ensuing the internationalization of Oman fish companies. The ban raises two concerns that the paper intends to answer: (i) how firms have responded to surmount the ban, and (ii) which strategies are more effective in the process of internationalization. The paper distinguishes three sets of actions: during the ban and immediate actions; short term actions; and long term actions. Besides government support for the implementation of international norms of quality and safety control, firms have responded individually to the EU ban. The actions subsequently undertaken by firms in response to the ban were selected: identification of new markets (alternatives); implementation of the required regulations and needed support to continue exporting to traditional European markets (competence); and long term business and marketing strategies (strategic thinking). These actions or steps represent the internationalization process or approach followed by the fisheries firms in Oman. All these actions have been undertaken after the EU ban, which leads to the conclusion that the ban has indeed worked as a driving force to internationalize, i.e. to develop the requisites of international markets

Internationalization of Oman Fisheries Firms After the European Union Ban

This paper examines the impacts of the l998 ban on Oman fish exports to the EU markets and ensuing the internationalization of Oman fish companies. The ban raises two concerns that the paper intends to answer: (i) how firms have responded to surmount the ban, and (ii) which strategies are more effective in the process of internationalization. The paper distinguishes three sets of actions: during the ban and immediate actions; short term actions; and long term actions. Besides government support for the implementation of international norms of quality and safety control, firms have responded individually to the EU ban. The actions subsequently undertaken by firms in response to the ban were selected: identification of new markets (alternatives); implementation of the required regulations and needed support to continue exporting to traditional European markets (competence); and long term business and marketing strategies (strategic thinking). These actions or steps represent the internationalization process or approach followed by the fisheries firms in Oman. All these actions have been undertaken after the EU ban, which leads to the conclusion that the ban has indeed worked as a driving force to internationalize, i.e. to develop the requisites of international markets. 

Constructing a Social Accounting Matrix: Concepts and Use in Economic Policy Analysis

The objective of this paper was to construct a social accounting matrix (SAM) and show how it can be used to determine the economy-wide and sectoral effects of external shocks and various policy options available using Oman as a model. We first constructed an aggregate SAM (macro SAM) based on the country’s national accounts which provided the control totals for a multisectoral, multi-institutional SAM. Then, we used the SAM to derive the multiplier matrix coefficients and simulated the effects of four policy scenarios: 1) an increase in agricultural and manufacturing exports (diversification scenario), 2) an increase in oil export value, 3) a reduction in worker remittances, and 4) an income transfer to rural households (equity scenario). Results showed that the diversification scenario had the largest overall production multiplier, while the increase in oil export price scenario had the highest impact on government revenue, balance of trade and saving. The remittance control scenario had the highest impact on total household income but most of the income increase went to urban households. The equity scenario had the second largest increase on household income, mostly rural income, but the least effect on saving, and trade balance. The policy implications of these simulations are not clear-cut. In addressing development issues, policy makers would need to use a combination of policy instruments to achieve a specific objective

Effect of Industrial Impregnation Process on the Magnetic Properties of Electrical Steels

International audienceThis paper deals with the experimental investigation of the effect of impregnation process on the normal magnetization curve and iron losses of electrical steels. To address this issue, several laminated toroidal magnetic circuits have been designed to characterize the magnetic properties with the flux metric method. The first configuration considers magnetic circuits wrapped with adhesive tape so that the dielectric resin will be deposited only on the outer surface of the magnetic circuit. In the second configuration, the magnetic circuits are unwrapped, which will allow the resin to diffuse within the inter-laminar spaces of the magnetic circuit. The obtained experimental results show significant effects on the magnetic properties in both cases. However, depending on the considered configuration, the resin diffusion also has an influence on the changes in magnetic properties

Floating thrombus in the ascending aorta revealed by peripheral arterial embolism

A floating thrombus in the ascending aorta is rarely found in clinical practice and is an uncommon cause of peripheral arterial embolization. When there is minimal atherosclerosis or a normal aorta, the management of such a lesion is poorly defined. Currently, there is no clear consensus concerning optimal treatment. Herein, we report 2 cases of ascending aortic thrombus that are complicated by a peripheral embolic event. Due to the risk of recurrent systemic embolism, particularly with strokes, surgical thrombectomy with ascending aortic wall replacements was performed. We believe that floating ascending aorta thrombus represents a serious source of systemic embolism and stroke. Surgical removal is easy to perform with good clinical outcomes. Conservative treatments such as anticoagulation or thromboaspiration may be considered in high-risk or inoperable patients