Showing papers by "Istanbul Technical University published in 2003"

Molecular biomimetics: nanotechnology through biology

Abstract: Proteins, through their unique and specific interactions with other macromolecules and inorganics, control structures and functions of all biological hard and soft tissues in organisms. Molecular biomimetics is an emerging field in which hybrid technologies are developed by using the tools of molecular biology and nanotechnology. Taking lessons from biology, polypeptides can now be genetically engineered to specifically bind to selected inorganic compounds for applications in nano- and biotechnology. This review discusses combinatorial biological protocols, that is, bacterial cell surface and phage-display technologies, in the selection of short sequences that have affinity to (noble) metals, semiconducting oxides and other technological compounds. These genetically engineered proteins for inorganics (GEPIs) can be used in the assembly of functional nanostructures. Based on the three fundamental principles of molecular recognition, self-assembly and DNA manipulation, we highlight successful uses of GEPI in nanotechnology.

Multi‐criteria supplier selection using fuzzy AHP

Abstract: A supplier selection decision inherently is a multi‐criterion problem. It is a decision of strategic importance to companies. The nature of this decision usually is complex and unstructured. Management science techniques might be helpful tools for these kinds of decision‐making problems. The aim of this paper is to use fuzzy analytic hierarchy process (AHP) to select the best supplier firm providing the most satisfaction for the criteria determined. The purchasing managers of a white good manufacturer established in Turkey were interviewed and the most important criteria taken into account by the managers while they were selecting their supplier firms were determined by a questionnaire. The fuzzy AHP was used to compare these supplier firms.

The Power of Statistical Tests for Trend Detection

Abstract: The existence of a trend in a hydrological time series is detected by statistical tests. The power of a test is the probability that it will reject a null hypothesis when it is false. In this study, the power of the parametric t-test for trend detection is estimated by Monte Carlo simulation for various probability distributions and compared with the power of the non-parametric Mann-Kendall test. The t-test has less power than the non-parametric test when the probability distribution is skewed. However, for moderately skewed distributions the power ratio is close to one. Annual streamflow records in various regions of Turkey are analyzed by the two tests to compare their powers in detecting a trend.

An integrated approach for supplier selection

Abstract: Competitive international business environment has forced many firms to focus on supply chain management to cope with highly increasing competition. Hence, supplier selection process has gained importance recently, since most of the firms have been spending considerable amount of their revenues on purchasing. The supplier selection problem involves conflicting multiple criteria that are tangible and intangible. Hence, the purpose of this study is to propose an integrated model for supplier selection. In order to achieve this purpose, supplier selection problem has been structured as an integrated lexicographic goal programming (LGP) and analytic hierarchy process (AHP) model including both quantitative and qualitative conflicting factors. The application process has been accomplished in a food company established in Istanbul, Turkey. In this study, the model building, solution and application processes of the proposed integrated model for supplier selection have been presented.

Virtual-topology adaptation for WDM mesh networks under dynamic traffic

Abstract: We present a new approach to the virtual-topology reconfiguration problem for a wavelength-division-multiplexing- based optical wide-area mesh network under dynamic traffic demand. By utilizing the measured Internet backbone traffic characteristics, we propose an adaptation mechanism to follow the changes in traffic without a priori knowledge of the future traffic pattern. Our work differs from most previous studies on this subject which redesign the virtual topology according to an expected (or known) traffic pattern, and then modify the connectivity to reach the target topology. The key idea of our approach is to adapt the underlying optical connectivity by measuring the actual traffic load on lightpaths continuously (periodically based on a measurement period) and reacting promptly to the load imbalances caused by fluctuations on the traffic, by either adding or deleting one or more lightpath at a time. When a load imbalance is encountered, it is corrected either by tearing down a lightpath that is lightly loaded or by setting up a new lightpath when congestion occurs. We introduce high and low watermark parameters on lightpath loads to detect any over- or underutilized lightpath, and to trigger an adaptation step. We formulate an optimization problem which determines whether or not to add or delete lightpaths at the end of a measurement period, one lightpath at a time, as well as which lightpath to add or delete. This optimization problem turns out to be a mixed-integer linear program. Simulation experiments employing the adaptation algorithm on realistic network scenarios reveal interesting effects of the various system parameters (high and low watermarks, length of the measurement period, etc.). Specifically, we find that this method adapts very well to the changes in the offered traffic.

Estimation, forecasting and extrapolation of river flows by artificial neural networks

Abstract: River flow forecasting and estimation provide basic information on a wide range of problems related to the design and operation of river systems. In this study the applicability of artificial neural networks (ANNs) to forecasting, estimation and extrapolation of the daily flow data belonging to the rivers in the East Mediterranean region of Turkey was investigated. Throughout the study a multi-layer perceptron network was used as the ANN structure. In the forecasting part of the study predictions one day and six days ahead were investigated. The extrapolation ability of ANNs, the prediction beyond the calibration range, was the next concern of the study. The ANNs were then implemented to investigate their generalization ability, i.e. the prediction of a different time series with the trained model. River flow estimation using data from nearby stations was the final application of the ANNs. From the graphs and statistics it is apparent that a neural network solution can provide a tighter fit to th...

A Web page prediction model based on click-stream tree representation of user behavior

Abstract: Predicting the next request of a user as she visits Web pages has gained importance as Web-based activity increases. Markov models and their variations, or models based on sequence mining have been found well suited for this problem. However, higher order Markov models are extremely complicated due to their large number of states whereas lower order Markov models do not capture the entire behavior of a user in a session. The models that are based on sequential pattern mining only consider the frequent sequences in the data set, making it difficult to predict the next request following a page that is not in the sequential pattern. Furthermore, it is hard to find models for mining two different kinds of information of a user session. We propose a new model that considers both the order information of pages in a session and the time spent on them. We cluster user sessions based on their pair-wise similarity and represent the resulting clusters by a click-stream tree. The new user session is then assigned to a cluster based on a similarity measure. The click-stream tree of that cluster is used to generate the recommendation set. The model can be used as part of a cache prefetching system as well as a recommendation model.

Hydrolysis and acidogenesis of particulate organic material in mesophilic and thermophilic anaerobic digestion

Abstract: The purpose of this study was to evaluate the effect of pH and inorganic nutrient supplementations for anaerobic hydrolysis and addogenesis of paniculate organic materials at both mesophilic (35 °C) and thermophilic (55 °C) temperatures. Hydrolysis and addogenesis of a synthetic sludge was observed in batch operation for the evaluation of the pH effect. pH was uncontrolled in one reactor and controlled at 4.5, 5.5, and 6.5 in the other three reactors at both temperatures. The greatest degree of hydrolysis and addogenesis occurred when the pH was controlled at 6.5. The pH of the uncontrolled reactor dropped to 3.4 at both temperatures severely retarding hydrolysis and addogenesis. Concentrations of acetic and n‐butyric adds predominated with lower concentrations of propionic add at both temperatures in all reactors. Lactic add was produced as the earliest intermediate but as the reaction proceeded, short chain VF As were produced as final end products with a decrease in lactic add. The higher the ...

The North Anatolian fault in the Sea of Marmara

Abstract: [1] Using the detailed geometry and tectonics of the Main Marmara fault that connects the Gulf of Izmit fault with the Ganos fault established by Le Pichon et al. [2001] and the new GPS data set recently analyzed by Meade et al. [2002], we confirm the existence of a Marmara block delimited to the north by the northern branch of the North Anatolian fault (the Marmara branch) and to the south by the southern branch. The kinematics of this block indicate that the Marmara branch that crosses the Sea of Marmara is close to pure dextral strike slip at a rate of 23 mm/yr on its whole length. The short Cinarcik section is the only one where a significant extensional component is predicted. A simple kinematic model accounts for slip partitioning there, with 8–10 mm/yr of extension to the south of the basin and 23 mm/yr of dextral strike slip along the northern Cinarcik margin. The new GPS data demonstrate the existence of important asymmetric elastic loading along the Main Marmara fault that may have significant implications for the seismotectonics of the area. The expected future large earthquake may rupture the whole main Marmara fault. The partitioning in the Cinarcik basin may produce magnitude 7 normal faulting earthquakes if their repetition time is about 250 years. The 1896 earthquake may have been one of these normal fault earthquakes. The Marmara block is less than 1 Ma. Prior to its formation, it was part of the Anatolian block. At this time the Ganos fault was already a dextral strike-slip fault, but the fault system in the Sea of Marmara would have been affected by an extensional component increasing toward the east that accounts for the increasing size of the sedimentary basins eastward.

One-Component Bimolecular Photoinitiating Systems, 2†

Abstract: The compounds 2-thioxanthone-thioacetic acid and 2-(carboxymethoxy)thioxanthone, bimolecular photoinitiators for free radical polymerization, are synthesized and characterized. Their capability to act as initiators for the polymerization of methyl methacrylate was examined. The postulated mechanism is based on the intermolecular electron-transfer reaction of the excited photoinitiator with the sulfur or oxygen atom of the ground state of the respective photoinitiator followed by decarboxylation. The resulting alkyl radicals initiate the polymerization. Structures of the photoinitiators.

Diversity in Entrepreneurship: Ethnic and Female Roles in Urban Economic Life

Abstract: The aim of this paper is to investigate the phenomenon of ethnic female entrepreneurship in urban economic life. The focus of the research is on the attitudes and behaviour of Turkish female entrepreneurs in Amsterdam. The main question we pose is: Are ethnic female entrepreneurs special ethnic entrepreneurs or special female entrepreneurs? This paper provides an answer to this question on the basis of field surveys. The results of the case study research on Turkish female entrepreneurs in Amsterdam show that the “ethnic female profile” is a “special female profile” and that Turkish female entrepreneurs are “special female entrepreneurs”, particularly in terms of their personal and business characteristics, and their driving forces and motivations. They appear to combine their ethnic opportunities with their personal characteristics (and other opportunities) in the urban market, and to perform successfully. This is also due to the fact that they have become service providers for not only their own ethnic groups, but also for other groups in the city.

Compressive behaviour of carbon fibre composite jacketed concrete with circular and non-circular cross-sections

Abstract: This paper describes the concentric compression test results of carbon fibre reinforced polymer (CFRP) composite sheet jacketed concrete specimens with circular, square and rectangular cross-sections. In the experimental program, pre-damaged specimens and repeated compressive loads were considered as well as undamaged specimens and monotonic compressive loads. The contribution of CFRP composite jackets to the compressive behaviour of the specimens is evaluated quantitatively, in terms of strength, longitudinal and lateral deformability and energy dissipation. Simple analytical expressions are proposed for compressive strength and ultimate axial strain that are valid for CFRP composite jacketed concrete with circular, square and rectangular cross-sections. The analytical results obtained by the proposed expressions are in good agreement with the experimental data obtained in this study, as well as the experimental data available in literature.

A review of the effects of dye‐assisting chemicals on advanced oxidation of reactive dyes in wastewater

Abstract: The effect of dye-assisting chemicals frequently used in the reactive dyeing process (i.e. chloride, carbonate and sulphate sodium salts) on the kinetics, reaction mechanism and efficiency of advanced oxidation processes has been discussed. The review begins with a brief description of various advanced oxidation processes, their chemistry and major application ranges, and continues with recent case studies reported for reactive dye degradation with advanced oxidation processes. Finally, experimentally-observed effects of dye-assisting chemicals on advanced oxidation rates have been kinetically ranked and compared to the inhibition rates of theoretically predicted advanced oxidation processes.

Employee satisfaction in higher education: the case of academic and administrative staff in Turkey

Abstract: The main purpose of this research is to explore the differences in satisfaction dimensions between the academic and administrative employees in higher education institutions in a developing country, Turkey. In this research, a state university in Istanbul was selected as the case. A total of 291 academic and administrative employees of the institution participated in the research conducted using the method whereby participants answered an original questionnaire. According to the results of the research, it has been found out that there are certain differences in factors such as “colleague relations satisfaction”, “colleague competition level satisfaction”, “other work group satisfaction”, “professional satisfaction”, “work environment satisfaction”, and “salary satisfaction” with respect to the satisfaction of academic and administrative employees.