On the Capacity Bounds of Undirected Networks

In this work we improve on the bounds presented by Li&Li for network coding gain in the undirected case. A tightened bound for the undirected multicast problem with three terminals is derived. An interesting result shows that with fractional routing, routing throughput can achieve at least 75% of the coding throughput. A tighter bound for the general multicast problem with any number of terminals shows that coding gain is strictly less than 2. Our derived bound depends on the number of terminals in the multicast network and approaches 2 for arbitrarily large number of terminals.Comment: 5 pages, 5 figures, ISIT 2007 conferenc

The effect of tool fixturing quality on the design of condition monitoring systems for detecting tool conditions

Condition monitoring systems of machining processes are essential technology for improving productivity and automation. Tool wear monitoring of cutting tools is one of the important applications in this area. In this paper, the effect of collet fixturing quality on the design of condition monitoring systems to detect tool wear is discussed. The paper investigates the difference in the system's behaviour and the changes in the condition monitoring system when the cutting tool is not rigidly fastened to the collet. A group of sensors, namely acoustic emission, force, strain, vibration and sound, are used to design the condition monitoring system. Automated Sensor and Signal Processing Selection (ASPS) approach1 is implemented to address the effect of the tool holding device (collet) on the monitoring system and the most sensitive sensors and signal processing method to detect tool wear. The results prove that the change in the fixturing quality could have significant effect on the design of the condition monitoring system and the behaviour of the system

Shear design of HSC beams with combination of links and horizontal web steel

The existing recommendations in Eurocode 2 and the British Code of Practice for the shear design of beams are derived from research conducted essentially on normal-strength concrete (NSC) with cube strengths up to 50 MPa, and it was found that the shear strengths of high-strength concrete (HSC) members made with limestone aggregate are below the characteristic resistances of identical NSC members. Previous experimental tests have also shown that significant differences exist in the angle of crack of shear failure of NSC and HSC. This paper presents data from five beam tests, which demonstrate that HSC with limestone aggregate has a reduced shear strength compared with NSC made with gravel and thus shows a gap in knowledge in the design approach to shear resistance of HSC beams. Previous investigations have suggested that horizontal web steels can contribute to the overall shear resistance of a reinforced concrete member in conjunction with the other constituents, concrete, tension and shear steel. The paper also presents data from tests on 11 beam tests and shows that the shear resistance of HSC beams is highly dependent on dowel action resulting from horizontal web bars positioned at the centre of the depth of the beam. Past attempts to quantify this dowel action are investigated and an improved design rule is proposed

Investigating the Impact of Nano-Calcined Halloysite on Concrete Durability under Chloride Attack

يشكل تأثير العوامل العدوانية، وخاصة الكلوريدات، على الهياكل الخرسانية تحديا كبيرا في مجال الهندسة. يؤدي وجود الكلوريدات إلى تآكل الخرسانة وتدهورها مما يؤثر على أدائها. تخترق الكلوريدات الخرسانة مما يؤدي إلى تدمير الطبقة الواقية حول حديد التسليح مما يؤدي إلى تآكل الفولاذ وتكوين الصدأ، يؤثر هذا التآكل سلبًا على قوة الارتباط بين الفولاذ والخرسانة ويمكن أن يسبب أيضًا تشققات على سطح الخرسانة، مما يقلل من متانتها, ولمواجهة هذا التحدي، تم إجراء دراسة بحثية لاستكشاف استخدام المواد النانوية، وتحديداً الهالويسايت المكلس النانوي، لتحسين أداء ومتانة الخرسانة. كان الهدف هو دراسة تأثير دمج الهالويسايت في الخرسانة على تغلغل الكلوريدات والتآكل اللاحق لقضبان حديد التسليح. تم فحص ثلاثة خلطات خرسانية مختلفة تحتوي على نسب متفاوتة من الهالويسيت (1.5%، 3%، 4.5%). وقام الباحثون بتقييم معدلات امتصاص الماء ومعاملات الهجرة لهذه الخلائط, بالإضافة إلى ذلك، تم استخدام تقنية التيار المسلط، حيث تم تطبيق تيار 14 مللي أمبير لمدة 26 يومًا لتسريع تآكل قضبان التسليح الفولاذية. أظهرت نتائج الدراسة فعالية دمج الهالويسيت في الخرسانة لتعزيز خواصه. حقق الخليط المحتوي على 3% و4.5% من الهالويسايت (CHNC) الأهداف المرجوة، مما أدى إلى تقليل امتصاص الماء بشكل كبير. على سبيل المثال، أظهر الخليط الذي يحتوي على %4.5 (CHNC) انخفاضًا بنسبة 42.99% في امتصاص الماء بعد 7 أيام. كما أدى هذا الانخفاض في امتصاص الماء إلى انخفاض كبير في معامل هجرة الكلوريدات واختراقها في الخرسانة. علاوة على ذلك، أدى إدراج 4.5% من الهالويسايت و25% من خبث الفرن العالي المحبب (GGBS) في الخليط إلى تحسين أداءه.The impact of aggressive agents, especially chlorides, on concrete structures is a significant challenge in the field of engineering. The presence of chlorides leads to corrosion and deterioration of concrete, affecting its performance. Chlorides penetrate the concrete, leading to the destruction of the protective layer around the reinforcing steel, which results in the corrosion of the steel and the formation of rust. This corrosion negatively affects the bond strength between the steel and the concrete and can also cause cracks on the concrete surface, reducing its durability. To address this challenge, a research study was conducted to explore the use of nanomaterials, specifically nano-calcined halloysite, to improve the performance and durability of concrete. The aim was to investigate the impact of incorporating halloysite in concrete on the penetration of chlorides and the subsequent corrosion of reinforcing steel rebars. Three different concrete mixtures containing varying percentages of halloysite (1.5%, 3%, and 4.5%) were examined. The researchers evaluated the water absorption rates and migration coefficients of these mixtures. Additionally, the impressed current technique was utilized, where a 14mA current was applied for 26 days to accelerate the corrosion of steel rebars. The results of the study demonstrated the effectiveness of incorporating halloysite in concrete to enhance its properties. The mixture containing 3% and 4.5% of halloysite (CHNC) achieved the desired objectives, significantly reducing water absorption. For example, the mixture with 4.5% CHNC showed a 42.99% reduction in water absorption after 7 days. This decrease in water absorption also led to a considerable decrease in the migration coefficient of chlorides and their penetration in the concrete. Furthermore, the inclusion of 4.5% halloysite and 25% ground granulated blast furnace slag (GGBS) in the mixture further improved its performance