Master of Science

thesisMore than 285,000 total hip replacement (THR) surgeries are performed in the United States each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to manufacture ultra-smooth articulating surfaces. In contrast, this work shows that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. A lubrication model is used to design the geometry of the patterned microtexture, and we experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints

Creating hydrodynamic lubrication in metal-on-polyethylene hip joints using surface microtexture

poste

The Modern Trends of International Tourism in the Baltic Region (on the Example of Latvia)

Розглянуто деякі аспекти розвитку міжнародного туризму в Латвії. Проаналізовано динаміку туристичних прибуттів у країну, географію в’їзного туризму, динаміку витрат іноземних туристів у розрізі окремих країн. Виділено види й форми туризму, які розвиваються випереджальними темпами на основі наявного туристично-рекреаційного потенціалу. Окреслено пріоритетні вектори розвитку туризму в Латвії. Some aspects of international tourism in Latvia is considered. The dynamics of tourist arrivals to the country, the geography of the inbound tourism, the dynamics of outlay of foreign tourists is analyzed. Types and forms of tourism, which developing leading position rates on the basis of tourism and recreational potential is highlighted. The priority vectors of development of tourism in Latvia is outlined

The Maximum Setup Time and Setup Cost of Achieving Just-in-Time System

The primary topic of operation management has turned to setup cost reduction because of the success of Just-in-Time (JIT) system. Setup cost is treated as a policy variable that can be reduced. A few papers prove that setup cost reduction will increase the number of setups and approach to JIT. However, those papers do not discuss the maximum setup time allowed that will successfully achieve to JIT. The Wagner-Whitin (WW) algorithm is known to produce optimal lot size for T-period dynamic lot-sizing problems. This paper develops an extension of the WW algorithm to establish a recursive model and find the sufficient and necessary conditions of yielding JIT. Furthermore, the limited maximum setup time that will yield JIT system is discussed. The maximum setup time of achieving JIT can be easily computed and understood in practice. The formula and table of the setup time allowed are obtained to act as a goal of reducing setup time in JIT system

B&W Call Admission Control for Multimedia Communication Networks

In the multimedia communication networks providing quality of service (QoS), an interface between the signal processing systems and the communication systems is the call admission control (CAC) mechanism. Owing to the heterogeneous traffic produced by diverse signal processing systems in a multimedia communication network, the traditional CAC mechanism that used only one CAC algorithm can no longer satisfy the aim of QoS CAC: Utilize the network resource to the most best and still satisfy the QoS requirements of all connections. For satisfying the aim of QoS CAC in the multimedia communication networks, this study proposed an innovative CAC mechanism called black and white CAC (B&W CAC), which uses two CAC algorithms. One of them is called black CAC controller and is used for the traffic with specifications more uncertain, which is called black traffic here. The other is call white CAC controller and is for the traffic with clearer specifications, which is call white traffic. Because white traffic is simple, an equivalent bandwidth CAC is taken as the white CAC. On the other hand, a neural network CAC (NNCAC) is employed to be the black CAC to overcome the uncertainty of black traffic. Furthermore, owing to more parameters needed in a QoS CAC mechanism, a hierarchical NNCAC is proposed instead of the common used NNCAC. Besides to accommodate more parameters, a hierarchical NNCAC can keep the complexity low. The simulation results show the B&W CAC can obtain higher utilization and still meet the QoS requirements of traffic sources