Sharif Digital Repository

One of the main arguments between scientific realists and scientific anti-realists is about observability. As a prominent anti-realist, van Fraassen and his theory of constructive empiricism and his views on observability and the use of scientific instruments, have been the subject of many debates. He believes that observation is the sole path to knowledge and observation is only possible through unaided human eye, so seeing through scientific instruments like microscopes does not count as observation, therefore the information gained from these procedures are not necessarily true.This thesis not only examines van Fraassen’s outlooks on the matter, but also examines his opponents’ view and... 

Titanium is the most widely used material in medical implants. One of the drawbacks of utilizing titanium in implants, is its biologically inert surface; which hinders the creation of the optimal bond between the implant and the surrounding tissue. This limitation can be addressed by altering the surface texture. As a technology, applying vibration to the tool or workpiece during machining operations is a practical method to create surface micro textures. Upon reviewing the existing literature, it is evident that the impact of the surface texture achieved by vibration-assisted milling, on the interaction of bone cells with the titanium surface has not been investigated. Therefore, this... 

In this piece of work, a gravity model is suggested as Iranian non-fuel export model to OIC countries. The most important results out of this model are the acquired coefficients of two variables, namely “ECO membership” and “Economic and Trade Freedom of Importer”. At first, we expected that for importer, being a member of ECO would increase the amount of trade with iran. Surprisingly, this is not what we see in a model. In fact, as ECO has not achieved any tangible success in increasing trade between its members, eastern Asian Muslim countries has become an important trade partner for iranians. This result is compatible with other pieces of researches about ECO. “Economic and Trade Freedom... 

In this thesis, we model and analyze coherent optical OFDM systems which are highly concerned as future fiber optic communication. To this end, we first introduce various applications of that in optical communication systems and investigate its probes and cones. In the rest of the thesis, we characterize the mathematical structure of the nonlinear phase noise and discuss the previous methods of compensation of that and propose some new ways of nonlinear phase noise compensation and equalization. And as we discuss each method we also investigate its computational complexity and BER performance. We propose three new phase noise compensation method, considering optical phase conjugation, we... 

Today’s growing interest to the underwater explorations and navigations demands to design appropriate underwater communication methods and systems. However, radio frequencies which are widely being used in free space communications, can’t be a good candidate for underwater wireless communications, due to their sever attenuation in water. On the other hand, underwater acoustic communication has been widely studied and implemented in the past decades, inspired by suitable propagation of acoustic waves through the underwater medium. Nevertheless, acoustic communication systems have limited bandwidth, lower propagation speed and lower security than optical counterparts, which suggests underwater... 

Utilizing ultrashort light pulses in optical communication systems can enhance the data rate or throughput in multiple access telecommunication systems. One of the most important challenges in ultrashort light pulse communication systems is the detection of such pulses among various types of noise in the receiver with conventional band-limited photodetectors which is proved to degrade the detection performance considerably. To overcome the aforementioned obstacle, contriving nonlinear optical preprocessors prior to the photodetector at the receiver is suggested. This preprocessor can increase the discrimination between ultrashort light pulse with high peak power and the noise with average... 

Tool condition Monitoring is done with the aim of reducing the cost and production time along with protect the quality of the machined product and the life of the tool. In this study, using the PCB333B30 vibration sensor and USB-4431 data logger and MATLAB software, the tool conditions in the milling process was examined. The selected feature is to monitor the status of the chatter. The data extracted from the sensor after processing was sent to a cloud user interface that designed on a website. The purpose of this study is to develop a system in which the user can observe the conditions of the tool (chatter occurrence) in real-time, over time and over place, just by access the... 

Past theory-changes in science were sometimes accompanied by radical conceptual shifts. This has urged some philosophers of science to project the same possibility onto current theories and suspend belief in the conceptual parts of our current best scientific theories. This type of argument is called the “pessimistic induction” (PI) and is often used by scientific anti-realists. Scientific realists, on the other hand, have argued against PI, by insisting that past theory-changes were not as radical as anti-realists suggest, as well as by appealing to the differences between current and past science. In recent decades, anti-realists, such as Kyle Stanford and Brad Wray, have renewed the... 

let Mn n be a positive semmi definite matrix and M:= (U; B) be a matroid. Consider the problem of finding S 2 B such that det(MS;S) is maximized, in witch MS; S is the submatrix of M, restricted to rows and columns of S. This problem has a variety of applications including page ranking algorithms. The problem above is an NP-hard problem in the general case. However, there are several approximating and estimating algorithms for some special cases, which are interesting. Also, exactly solving the problem is NP-hard, even for some special matroids. As an example, one can consider the uniform matroids. Khachiyan introduced a greedy algorithm with dd approximation factor. Afterward, Di summa et... 

The importance of the issue of laws of nature is obvious so that some say the purpose of science is discovering the laws of nature. In his “laws and symmetry” (1989) van Fraassen takes an antirealistic position toward the laws. His project is to clear science from metaphysics, and since the notion of laws of nature has heavy metaphysical presuppositions it should be eliminated from the literature of science. He tries to provide three kinds of arguments against the notion of laws: first, historical arguments, second, arguing in favor of insufficiency of all presented accounts of laws, and third, rejecting the tasks that accounts of laws should do. In van Frassen’s view, studies of science... 

Visible light communication (VLC) uses huge license-free spectral bandwidth of visible light for high-speed wireless communication. Since each VLC access point covers a small area, handovers of mobile users are inevitable. In order to deal with these handovers, developing fast and effective resource allocation algorithms is a challenge. this paper introduces the problem of mobility-aware optimization of resources in hybrid VLC and 5G radio access technologies networks using the T-step look-ahead policy and employing the notion of handover efficiency. It is shown that the handover efficiency can correlate the overall performance of the network with future actions based on the mobility of... 

We know that Science has been one of the most influential cultural revolutions in recent centuries, and that, due to its remarkable successes and achievements, it has rapidly spread across many societies and cultures. Scientific theories have attracted the attention of many thinkers, but among these theories, Darwin's theory of evolution has attracted more attention in that it also claims to explain the origin of humans. One outcome of this theory is that man, and consequently all his attributes, including his cognitive powers, language, and culture (which are unique among the attributes of other species), came into being through a process of evolution and natural selection. But can the... 

In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract... 

Nowadays, metallic microsystems such as miniature and meso-scale gears, microgrippers, and comb structures constitute a significant portion of key components in various microelectromechanical systems (MEMS). Due to their extremely lightweight nature, small size, high dimensional accuracy, superior performance, and extended lifetime, the manufacturing process of these microsystems has always been a subject of discussion and research. The goal is to enhance the strength and precision of the products while reducing production costs.LIGA and wire-cut electrical discharge machining (WEDM) are two well-known methods for fabricating microstructurs. Despite their advantages, such as high dimensional... 

Laser-assisted mahining is a process whose positive impact on metal cutting has been repeatedly demonstrated. In recent years, with a significant reduction in the cost of laser technology, the necessity of utilizing this technology in machining materials that are not as difficult to cut as superalloys and ceramics, but still present unique challenges, has become evident. In this study, the laser-assisted machining process on LVM316 stainless steel alloy is comprehensively investigated. This alloy, due to its very low impurities and excellent corrosion resistance, has medical applications and is used in the manufacture of implants and medical equipment. However, because of these very... 

Descriptive complexity refers to the difficulty of expressing a problem in a formal language, allowing for a complete and precise description of the problem, including output specifications for function problems. Despite the success of the descriptive approach in computational complexity, this approach has been predominantly used for decision problems. In contrast to decision problems, a counting problem can be considered as a function with the range of natural numbers. This thesis focuses on the examination of counting problems from a descriptive perspective, exploring the connection between their descriptive and computational versions. Toward this goal, weighted logic is utilized to... 

The No-Miracle Argument (NMA), the primary argument employed by realists to support their position, has been understood in two different ways: as a kind of IBE and as a probabilistic argument. Following an overview of this argument and its status, this dissertation addresses and evaluates the most recent version of NMA given as a kind of IBE, as well as the many versions of its probabilistic forms. I then move on to the criticisms of the NMA's probabilistic forms. Among these criticisms, I have devoted three chapters on the base rate fallacy, which has received little attention to date. In the first of these three chapters, I discuss the base rate fallacy criticism and the responses of...