High-performance flat-type InGaN-based light-emitting diodes with local breakdown conductive channel

Flat-type InGaN-based light-emitting diodes (LEDs) without an n-type contact electrode were developed by using a local breakdown conductive channel (LBCC), and the effect of the In content of the InGaN quantum wells (QWs) on the local breakdown phenomenon was investigated. Electroluminescence and X-ray analyses demonstrated that the homogeneity and crystallinity of the InGaN QWs deteriorated as the In content of the InGaN QWs increased, thereby increasing the reverse leakage current and decreasing the breakdown voltage. After reverse breakdown with a reverse current of several mA, an LBCC was formed on the GaN-based LEDs. The surface size and anisotropic shape of the LBCC increased as the indium content of the InGaN QWs in the LEDs increased. Moreover, a flat-type InGaN LED without an n-type electrode was developed by using the LBCC. Notably, the resistance of the LBCC decreased with increasing indium content in the InGaN QWs, leading to lower resistance and higher light emission of the flat-type InGaN-based LEDs without an n-type contact electrode.

Experimental Tests for the Analysis of the Load-Bearing Capacity of an Internal Slab-Column Connection after its Punching at Various Positions of the Column

Normally, in practice the situation of a slab-column structure is rarely analyzed after the occurrence of a local breakdown. Catastrophes which have happened so far indicate the need of considering in detail slab-column connections in reinforced concrete structures in order to prevent progressive collapses. Some suggestions concerning the prevention of such situations are to be found merely in CSA A23.3-04 and ACI 318. This problem is not dealt with in the Polish Standards, nor in the Eurocodes. The paper presents the results of investigations performed on a model of slab-column connections in the scale 1:1. Three variants of the position of the column in relation to the centre of the slab have been considered: the axial position, the position in an unidirectional eccentricity, and in bidirectional eccentricity. The tests were performed in two phases, viz. "Phase 1" preceding the punching and "Phase II" after punching to the complete destruction of the connection. The aim of these investigations was to find out how far any additional bending moment resulting from the eccentric effect of the load affects the value of the destructive load imposed on the connection after its punching. The obtained results permitted to determine the relations between the exerted load and the displacement of the column in time, and also to determine the values of the force at which the rupture of the bars above the column had taken place. The results of these tests were compared with the standard.

Compressor Instability: Stall, Surge and their Control

Every compressor has a stall line. In the vicinity of the stall line, the flow field is inherently unsteady due to the interactions between adjacent rows of blades, formation of small stall cells, flow separation and the viscous effects including shock-boundary layer interactions. These factors may aggravate to a state of local breakdown of flow or a total breakdown of flow or with a disastrous flow reversal. This paper starts with an overview on the previous researches about compressor stall and surge. Subsequently, it describes the effects of these instabilities in overall engine performance and design with/ without any control. The main objectives of this paper are to review the phenomenon of instability and methodology to suppress the rotating stall and surge by enlarging the stable operating range of compressor with the application of various control systems. This paper surveys research developments in this field and also tries to find an improved solution to increase the engine performance by applying various surge control strategies. Finally, the paper focuses on some recommendations towards a better design of compressor especially for aircraft power plant.