Sharif Digital Repository

Polylactic acid (PLA) is a biocompatible polymer that could be used for biomedical applications. Carbon nanotubes (CNT) have excellent mechanical strength and modulus and also are electrically conductive. Inclusion of CNT in PLA could improve mechanical and electrical properties of PLA and find applications as biomaterials in biomedical engineering. The success of the resulted nanocomposites of PLA/CNT depends on uniform dispersion of CNT within PLA and good interfacial adhesion between the nanotubes and the matrix PLA. Chemical modification of CNT surface by grafting maleic anhydride has been reported. However, for biomedical applications chemical agents may prove harmful and should be... 

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... 

Thermalization or the approach to thermal equilibrium in isolated many-body quantum systems is a fundamental problem in quantum statistical physics. There are various quantum systems, whose properties can be described on the basis of statistical mechanics, but there are also systems in which the thermal equilibrium is not realized.Those, that are integrable or systems that exhibit many-body localization (MBL) due to strong disorder, represent non-thermalized phase. Recent theoretical studies have revealed that integrability and the existence of a static disorder are not necessary conditions for the violation of thermalization, while there are translationally invariant and non-integrable... 

Quantum spin liquid (QSL) is an exotic phase of some frustrated magnetic Mott insulators. In this phase, competing interactions result in strong quantum fluctuations which prevent the formation of long-range order even at absolute zero temperature. However, QSL is not solely defined by the absence of order. In the modern definition, it is characterized by fractionalized excitations and emergent gauge fields. The signature of fractional excitations is evident in the form of a broad continuum in conventional probes. However, the continuum spectrum in QSL candidate materials does not definitively indicate whether the continuum is due to fractional excitations or usual ones. Recent theoretical... 

According to Haldane Conjecture Antiferromagnetic Heisenberg Spin Chain with integer spin has an energy gap, and exponential decay of correlation functions , while half integer spin chains are gapless with algebraic decay of correlation functions. A spin chain with two types of spins and Heisenberg interaction shows a mixture of both types of behavior. A ferrimagnet which is composed of two spins (S, s) has two bands of energy, the lower band is gapless and ferromagnetic property while the upper one is gapful with antiferromagnetic behavior. In the present work we have studied the anisotropic ferrimagnet in the presence of a transverse magnetic field. We have shown that the spin wave theory... 

Nowadays, considering intense competition and the need for continuous improvement in organizations, research and development projects have attracted the attention of many organizations. Due to the intense competition and turbulence in the competitive market, there is a need for flexibility in the strategic decisions. In this thesis, we introduce a systematic framework for executive decision making within a strategic planning framework using the real options valuation method. This two-stage model first takes value of strategic projects in different periods considering the market effects of using the real options opportunity approach. Then the effect of this selection on all the options is... 

Pulsating heat pipes (PHP) are complex heat transfer devices which unlike conventional heat pipes do not contain any wick in their structure. The effective parameters consist of; working fluid, volumetric filling ratio, operational orientation and input heat power have been investigated here. The experimental set-up we have contemplated, fabricated and tested included five turns, made of copper tube coupled with two glass tube of internal diameter 1.8 mm. The height of evaporator, condenser and adiabatic section was 60, 60 and 150 mm, respectively. The evaporator was heated with electrical element connected to an AC variant power supply and the condenser was connected to a constant... 

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... 

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... 

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... 

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... 

Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the... 

Lithium has 9 isotopes which two isotopes are stable and remaining isotopes are unstable and have half-life. Lithium stable isotopes include 6Li and 7Li that their abundance is 7.53% and 92.47% respectively. Importance of lighter lithium isotope appears for its small cross section against thermal neutron and producing fusion reactors fuel in nuclear industries. Thermal neutron absorption cross section for 6Li and 7Li are 950 barn and 37 mbarn respectively. Interesting of these isotopes in nuclear industry is due to the large difference in the absorption cross section.6Li compounds implied for tritium producing in coat of nuclear fusion reactor with DT fuel. Following tritium is used in... 

The purpose of the present project is to construct and improve the quality of an absorbable membrane using a supercritical process and study the effects of the operative parameters. Today, usage of biodegradable polymers is intensively increasing and these kinds of polymers are used as drug delivery carrier and tissue engineering medium. A biodegradable membrane is suitable for this goal. In this study Poly Ethylene Glycol (PEG) is used as the biodegradable polymer. Gas anti-solvent (GAS) method was applied for the production of the membrane. The used anti-solvent was Supercritical Carbon Dioxide. In order to study the effects of the operative parameters on the structure of the produced... 

Reducing fossil fuels and increasing urban air pollution, has made the automotive industry to reduce the fuel consumption of their engines by various approaches. Removing the compressor of air conditioning system by replacing the absorption chiller instead of inverse rankin cycle is a shortcut to reduce the fuel consumption which at the same time reduces costs of using air conditioning system for occupants. Design of a 3 kW lithium bromide-water absorbent chiller has verified based on environmental conditions and car space limitations and using the combustion products as the heat source of system. K4M engine of L90 sedan Car as an internal combustion engine sample’s exhaust manifold has been... 

Nowadays Lab-on-a-chip systems are being widely used in medical applications, especially in analyzing minute volumes of blood for diagnosis and treatment of some crucial diaseses like diabetic. A Lab-on-a-chip is comprised of a variety of components such as micromixer, microdispenser, detection and separation units and so on. In this thesis, however, we have analyzed and numerically simulated a microdispenser which is electrokinetically driven. In other words, electrical potentials are applied to electrodes in order to conduct two fluids within a cross microchannel, and distribution of a sample fluid takes place due to appropriately applied potentials. In order to analyze and simulate the... 

Various application of polyethylene material in different industries caused to modern techniques for controlling and measuring specifications of micro-particle suspension. Many industries try to increase stability of suspensions in front of their phase separation.
Because of the consequences of suspension homogeneity, at first, we measured this property. Then, the stability was tested by three different methods. In the first method, the transmitted laser light was measured to assay the suspensions stability. In the second, number of sediments of particles was counted. Sedimentation velocity of particles was measured directly by using a horizontal microscope as the third method. The... 

Foil gas bearings are compliant surface, self-acting hydrodynamic bearings that use ambient gas as their working fluid. They do not require external pressurization and are typically constructed from several layers of sheet metal foils. In high-speed, high-temperature applications the GFB’s have the advantage of developing higher load capacities than with fixed geometry gas bearings. Since GFB’s have a complex structure consisting of a spring-like substructure with an overlying flexible surface, there exists a great variety of permutations on any given design. At current work presents a 1D model for GFB with couple solving Reynolds and Euler-Bernoulli beam equation. This mean top foil assume to... 

Lameness in dairy cattle is a crucial welfare issue in dairy industry, and over the years scientists are attempting to present a detection method. In recent years it is attracting more attention to make the identification and discrimination of sounds and lames systematic and automatic. Right now, the most hopeful results have been obtained through the measurement of Ground Reaction Forces (GRF) of hooves, and analysis of load distribution between four legs, which seems applicable for wide use in dairy industry. However, the accuracy, validity, and reliability of discrimination is still far from an acceptable point, that is because of a great lack in understanding quantitative effects of the... 

Natural boron consists of two stable isotopes, mass 10 (19.3%) and mass 11 (80.7%). 10B isotope has a large thermal neutron capture cross-section and it therefore, used widely in such aspects as modern industry, military equipment, medical science and so on. specially the demand of atomic energy industry for the boron isotope is increased severely. So the separation of 10B from natural boron has received very wide attention at present. There are many kinds of methods on the boron isotopes separation, such as chemical exchange reaction and distillation in boron trifluoride method, ion exchange in boric acid solution method, counter current recycle membrane cascades in boron trifluoride...