Heat pipe is a passive two phase device capable of transferring large rates of heat with a minimal temperature drop. It is a sealed tube with a wick structure lined in it and with a working fluid inside the tube. It consists of three parts: an evaporator, a condenser and an adiabatic section. The heat pipes are widely used in electronics cooling and spacecraft applications. Although they can transfer large rate of heat in a short range, they have operating limits, namely: the capillary limit, the viscous limit, the entrainment limit, the sonic limit and the boiling limit. These limits determine the heat transfer capacity of the heat pipe. The properties of the working fluid, the structure of the wick, the orientation of the pipe, the length and the diameter of the tube etc. are the parameters that affect the limits. In this study, an analytical 1-D heat pipe model is formed and a computer code is prepared in order to analyze the effects of the parameters on the heat transfer capacity of a heat pipe. Water, Ammonia and Mercury are investigated as working fluids for different operating temperature ranges. The software is tested for a typical application for each working fluid.

The aim of this study is designing steel structures with the same geometry, material and soil conditions but in the different countries, and comparing these designs in terms of material savings. According to three steel building codes, namely TS 648, LRFD, Eurocode 3, same structures with various stories (2, 4, 6, 8, and 10) are analyzed and designed. To calculate the design loads, Turkish Earthquake Code 2007 and Turkish Standard 498 (Design Load for Buildings) are utilized when TS 648 is applied. When LRFD is concerned, ASCE Standard 7-05 (Minimum Design Loads for Buildings and Other Structures) and AISC Standard 341-05 (Seismic Provisions for Structural Steel Buildings) are used for calculation of the design loads and earthquake loads. When Eurocode 3 is applied, Eurocode 8 (Earthquake Resistance Code), Eurocode 1 (Actions of Structures) and Eurocode-EN 1990 (Basis of Structural Design) are used in order to determine the design and earthquake loads. Weight of steel used on 1 m&sup2 / is almost the same for procedures of LRFD and EC3. It is important to note that those procedures consider 20 % of material saving compared to TS648.

Recent devastating earthquakes revealed that bridges are one of the most vulnerable components of the transportation systems. These seismic events have emphasized the need to mitigate the risk resulting from the failure of the bridges. Depending on the seismicity of the bridge local site, seismic vulnerability assessment of the bridges can be done based on the fragility curves. These curves are conditional probability functions which give the probability of a bridge attaining or exceeding a particular damage level for an earthquake of a given intensity level. In this dissertation, analytical fragility curves are developed for the ordinary highway bridges in Turkey constructed after the 1990s to be used in the assessment of their seismic vulnerability. Bridges are first grouped into certain major bridge classes based on their structural attributes and sample bridges are generated to account for the structural variability. Nonlinear response history analyses are conducted for each bridge sample with their detailed 3-D analytical models under different earthquake ground motions having varying seismic intensities. Several engineering demand parameters are employed in the determination of seismic response of the bridge components as well as defining damage limit states in terms of member capacities. Fragility curves are obtained from the probability of exceeding each specified damage limit state for each major bridge class. Skew and single-column bent bridges are found to be the most vulnerable ones in comparison with the other bridge classes. Developed fragility curves can be implemented in the seismic risk assessment packages for mitigation purposes.

The main purposes of this study is to investigate first year calculus students&rsquo / understanding of formal limit concept and change in their understanding after limit instruction designed by the researcher based on APOS theory. The case study method was utilized to explore the research questions. The participants of the study were 25 students attending first year calculus course in Middle East Technical University in Turkey. Students attended five weeks instruction depending on APOS theory in the fall semester of 2007-2008. Limit questionnaire including open-ended questions was administered to students as a pretest and posttest to probe change in students&rsquo / understanding of limit concept. At the end of the instruction a semi-structured interview protocol developed by the researcher was administered to all of the students to explore students&rsquo / understanding of limit concept in depth. The interview results were analyzed by using APOS framework. The results of the study showed that constructed genetic decomposition was found to be compatible with student data. Moreover, limit instruction was found to play a positive role in facilitating students&rsquo / understanding of limit concept.

The cut slopes at a segment between Km 25+600 and 26+000 of the Antalya-Burdur Breakaway-Korkuteli State Road to be newly constructed have slope instability problems due to the existence of highly jointed limestone. The purpose of this study is to investigate the engineering geological properties of the units exposed at three cut slopes, to assess stability of the cut slopes, and to recommend remedial measures for the problematic sections. In this respect, both field and laboratory studies have been carried out. The limestone exposed at the cut slopes are beige to gray, fine grained, fossiliferous, and highly jointed. It has two joint sets and a bedding plane as main discontinuities. The kinematic analysis indicates that planar failure is expected at Km: 25+900. Limit equilibrium analysis show that the cut slopes with bench have no slope instability problems except rockfalls which endanger the traffic safety. In this thesis it is recommended to covering the cut slope with wire mesh and fibre reinforced shotcrete

Designing with Limit Equilibrium Methods involve a factor of safety (FS) in order to maintain the stability and to keep the resisting structure away from limit state on the safe side. Finite Element Program (such as Plaxis) on the other hand, instead of an FS, reduces the shear strength of the soil by introducing a reduction factor that is applied to tan

Mathematica is an extremely powerful and flexible symbolic computer algebra system that enables the user to deal with complicated algebraic tasks. It can also easily handle the numerical and graphical sides. One such task is the derivation of moment generating functions (MGF) and characteristic functions (CF), demonstrably effective tools to characterize a distribution. In this paper, we define some rules in Mathematica to help in computing the MGF and CF for linear combination of independent random variables. These commands utilizes pattern-matching code that enhances Mathematica's ability to simplify expressions involving the product of algebraic terms. This enhancement to Mathematica's functionality can be of particular benefit for MGF and CF. Applications of these rules to determine mean, variance and distribution are illustrated for various independent random variables.

This dissertation is devoted to groups generated by bounded automata and geometric objects related to these groups (limit spaces, Schreier graphs, etc.). It is shown that groups generated by bounded automata are contracting. We introduce the notion of a post-critical set of a finite automaton and prove that the limit space of a contracting self-similar group generated by a finite automaton is post-critically finite (finitely-ramified) if and only if the automaton is bounded. We show that the Schreier graphs on levels of automaton groups can be constructed by an iterative procedure of inflation of graphs. This was used to associate a piecewise linear map of the form fK(v) = minA[set]KAv, where K is a finite set of nonnegative matrices, with every bounded automaton. We give an effective criterium for the existence of a strictly positive eigenvector of fK. The existence of nonnegative generalized eigenvectors of fK is proved and used to give an algorithmic way for finding the exponents λmax and λmin of the maximal and minimal growth of the components of fK(n)(v). We prove that the growth exponent of diameters of the Schreier graphs is equal to λmax and the orbital contracting coefficient of the group is equal to 1/λmin . We prove that the simple random walks on orbital Schreier graphs are recurrent. A number of examples are presented to illustrate the developed methods with special attention to iterated monodromy groups of quadratic polynomials. We present the first example of a group whose coefficients λmin and λmax have different values.

No description available.

<p>Occupational Exposure Limits (OELs) are used as an important regulatory instrument to protect workers’ health from adverse effects of chemical exposures. The OELs mirror the outcome of the risk assessment and risk management performed by the standard setting actor. In paper I the OELs established by 18 different organisations or national regulatory agencies from the industrialised world were compared. The comparison concerned: (1) what chemicals have been selected and (2) the average level of exposure limits for all chemicals. In paper II the OELs established by 7 different national regulatory agencies of EU member states are compared to those of the European Commission (EC). In addition to the same comparisons as performed in the first study a comparison level was introduced (3) the similarity between the OELs of these EU member states and the OELs recommended by the EC.</p><p>List of OELs were collected through the web-pages of, and e-mail communication with the standard-setting agencies. The selection of agencies was determined by availability of the lists. The database of paper I contains OELs for a total of 1341 substances; of these 25 substances have OELs from all 18 organisations while more than one third of the substances are only regulated by one organisation alone. In paper II this database was narrowed down to the European perspective.  The average level of OELs differs substantially between organisations; the US OSHA exposure limits are (on average) nearly 40 % higher than those of Poland. Also within Europe there was a nearly as large difference. The average level of lists tends to decrease over time, although there are exceptions to this. The similarity index in paper II indicates that the exposure limits of EU member states are converging towards the European Commission’s recommended OELs. These two studies also showed that OELs for the same substance can vary significantly between different standard-setters. The work presented in paper III identifies steps in the risk assessment that could account for these differences. Substances for which the level of OELs vary by a factor of 100 or more were identified and their documentation sought for further scrutiny. Differences in the identification of the critical effect could explain the different level of the OELs for half of the substances. The results reported in paper III also confirm the tendency of older OELs generally being higher. Furthermore, several OELs were more than 30 years old and were based on out-dated knowledge. But the age of the data review could not account for all the differences in data selection, only one fifth of the documents referred to all available key studies. Also the evaluation of the key studies varied significantly.</p>