The Horn of Africa includes four countries: Somalia, Ethiopia, Eritrea, and Djibouti. One of the problems in this region is the border and territorial Conflicts and its insecurities in the border areas of the countries. Various factors are effective in creating this instability and border insecurity. Among them, history, historical mentalities, and the role of colonial history is significant. This research is a descriptive-analytical study that uses library resources to investigate the role of history in creating border insecurity with a case study of the role of colonialism in border insecurity in the Horn of Africa. The dependent variable of the research is border insecurity and independent variables are history, colonial history, and the Horn of Africa region. The main question is what is the role of history and historical changes in creating border insecurity in the Horn of Africa? In the Horn of Africa, the most important border conflicts and insecurities include border clashes between Ethiopia and Eritrea; Djibouti and Eritrea; and the insecurity has been caused by ethnic and tribal conflicts in the Somalia-Kenya border areas. The research results show that the history, colonial history, and actions of the colonial powers in drawing the borders of the countries, especially in the Horn of Africa region, which is based on colonial interests and not local interests, it has played an important role in border disputes between countries and instability and insecurity in border areas.

Due to its geographical location and vital dependence on the Nile River, Egypt considers its presence and influence in the Horn of Africa to be part of its national security and geopolitical strategy. This region, which includes the countries of Ethiopia, Somalia, Djibouti, Eritrea and Sudan, due to its proximity to the Red Sea and the Bab al-Mandab Strait, has become a focal point in strategic competitions between regional and international powers. This research, using the descriptive-analytical method and using the conceptual framework of strategic culture, seeks to answer this question: How has Egypt's attitude as a regional power in the Arab world and Africa influenced the country's policies in the Horn of Africa? This research argues that Egypt's strategic culture, which emphasizes the country's role as a central power in the Arab world and Africa, has led this country to more aggressive policies and increased presence in the Horn of Africa in order to consolidate its leadership role and influence the powers Limit the competitor.

Since the invention of ultrasonic vibration assisted turning, this process has been widely considered and investigated. The reason for this consideration is the unique features of this process, which include reducing machining forces, reducing wear, and friction, increasing the tool life, creating periodic cutting conditions, increasing the machinability of difficult-to-cut material, increasing the surface quality, creating a hierarchical structure (micro-nano textures) on the surface and so on. Different methods have hitherto been used to apply ultrasonic vibration to the tip of the tool during the turning process. In this research, a unique horn has been designed and constructed to convert linear vibrations of piezoelectrics to three-dimensional vibrations (longitudinal vibrations along the z axis, bending vibrations around the x axis, and bending vibrations around the y axis). The advantage of this ultrasonic machining tool compared with other similar tools is that in most other tools, it is only possible to apply one-dimensional (linear) and two-dimensional (elliptical) vibrations, while this tool can create three-dimensional vibrations. Additionally, since the nature of the designed horn can lead to the creation of three-dimensional vibrations, there is no need for piezoelectric half-rings (which are stimulated by 180 phase difference) to create bending vibrations around the x and y axes. The reduction of costs as well as simplicity of applying three-dimensional vibrations in this new method can play an important role in industrializing the process of three-dimensional ultrasonic vibration assisted turning.

Today, the application of ultrasonic tools in various processes such as machining, welding, homogenizing, etc., has become widespread. One of the most important and key components in the transfer of acoustic energy in emulsion homogenization applications is the ultrasonic horn. This part is stable from the point of view of energy, but the amount of vibration amplitude can be changed by changing the shape and material. The purpose of this paper is to analyze the multistage ultrasonic horn to achieve the desired vibration amplitude in various applications. Optimal horn design has been done with the aim of increasing the amplitude of vibration, increasing and distributing the wave transmission surface and considering the strength of the horn, the appropriate length to diameter ratio to achieve uniform cavitation in the emulsion. The goal is to achieve a horn with a high amplification factor and a larger and wider radiation area at the end and lateral area of the horn. The high vibration amplitude and wave propagation area at the tip and the lateral area of the horn increase the amount of cavitation in the emulsion process, and the wider the wave propagation regions, the more efficient the homogenization process will be.