Comparison of different disk searching methods

The efficiency of various disk file processing methods is compared. Serial search and activity frequency ordered list processing, direct access and merged sequential processing are compared and the increase in processing time due to overflow records is calculated. Relationships are given to decide which method is faster in practice for concrete data sets and devices.     

Collaborative learning in the clouds

Cloud computing has emerged as one of the most highly discussed topics both in the academic community and in the computing industry. While most of the work that has been conducted to explore this field focuses either on establishing the basis for cloud computing or almost exclusively on the issues surrounding security and data privacy, this paper takes the first exploratory step into exploring the actual internal working of cloud computing and demonstrates its viability for organizations, more specifically educational establishments . The paper starts by introducing the most important key clouds computing concepts, including virtualization technologies, Web services and Service Oriented Architectures (SOA), and distributed computing. Light will be then shed on the impact and potential benefits of cloud computing on teaching and learning in educational institutions. The paper closes by describing building a private cloud inside educational institution and highlights its offerings for students, staff and lecturers.     

The effectiveness of diaphragmatic pedicled grafts in esophageal injuries and wall reconstruction

BACKGROUND: In the early 1990s cases of tuberculosis in people with HIV infection and AIDS were undernotified. A study to evaluate changes in notification rates in two inner London local authorities was undertaken for the period January 1993-June 1996 inclusive. METHODS: For residents of the two local authorities, tuberculosis notifications were identified using a local database, and cases of AIDS with a recorded diagnosis of tuberculosis were identified from AIDS case reports. RESULTS: During the study period, only 13 (32 per cent) of the 41 AIDS cases with a recorded diagnosis of tuberculosis were also notified as a case of tuberculosis. However, the proportion of notified cases rose from 0 per cent (0 of 11) in 1993 to 50 per cent (5 of 10) in 1995 and 63 per cent (5 of 8) in early 1996. CONCLUSION: The increase in the tuberculosis notification rate for people with AIDS is encouraging, but scope for improvement remains.     

Detection of ATP-induced nitric oxide in a biomimetic circulatory vessel containing an immobilized endothelium

Conditions for the adhesion of bovine pulmonary artery endothelial cells (bPAECs) in microbore tubing of 250-microm i.d. are described. When immobilized to the lumen of microbore tubing, these cells represent a mimic of a circulatory vessel's endothelium. The microbore tubing is coated with 100 microg mL(-1) fibronectin in order to promote bPAEC adhesion to the lumen of the tubing. A series of micrographs of the cells inside of the tubing indicates that approximately 3.5 h is necessary for cell adhesion. In this study, adenosine triphosphate (ATP) is used to induce the release of nitric oxide from the endothelium mimic. The endothelium-derived NO is detected amperometrically at a parallel flow cell containing a glassy carbon working electrode modified with Nafion. Results indicate that detectable amounts of NO are only produced by the endothelium mimic when ATP is present in the buffer. The typical concentration of NO produced by the endothelium mimic upon the introduction of 100 microM ATP is approximately 0.80 microM. Based on the injection volume of ATP and the estimated number of cells on the tubing lumen, this value corresponds to approximately 1 amol of NO/cell. Moreover, shear stress alone does not provide the agonistic effect required for NO production in the submicromolar range.     

TRANSIENT FLOW OF A COMPRESSIBLE FLUID THROUGH BEDS OF SOLID PARTICLES OR POROUS MATERIALS

The problem of transient gas flow through porous structures is a typical one in many practical applications e.g. gas production from an underground reservoir, gas flow through the soil after an underground nuclear explosion or gas flow through a packed column. This later application is important for separation processes called Rapid Pressure Swing Adsorption (RPSA) and Pressure Swing Adsorption (PSA) where the course of the column pressurization strongly affects the mass transfer between the gas and either the adsorbent or the molecular sieve.

A mathematical model for the isothermal transient flow of an ideal gas through a solid bed or porous material has been compared with experimental results both in Darcy's region and in the high velocity region. Numerical simulations have been used to study the effect of the fixed bed characteristic parameters on the pressurization course of a fixed bed column closed at one end and connected to the constant pressure vessel on the other end. In four limiting cases the results have been interpreted using simple algebraic equations.

The theoretical analysis proved that for the particles being tested (d_p smaller than 0·7  mm) the effect of macroscopic inertia forces and nonisothermal effects are negligible under the following conditions: Input pressure smaller than 600  kPa and the ratio of inlet to initial pressure smaller than 20.     

Observer-Based Optimal Control of Flexible Stewart Parallel Robots

The design and simulation of two optimal control schemes for a parallel flexible link manipulator of the Stewart type is presented. The first control scheme combines a nonlinear rigid model of the flexible manipulator with a linear rigid observer, whereas the second scheme uses a nonlinear flexible manipulator model with a linear flexible observer. The majority of the results available in the literature do not address the optimal control problem through the use of observers, as it is done in this paper, for the control of parallel robots. The simulation results have shown in both cases that indeed optimal state-obscrver-based control is a good candidate for controlling parallel-link manipulators in practice. As expected, the second scheme (flexible model plus flexible observer) gives better results than the first one, achieving faster trajectory tracking. The effects of white noises, applied forces, and zero gravity environment were taken under consideration.