Integrated Photonics Structure for THz Systems Based on Silicon and Photoconductive Material

The field of terahertz (THz) technology has been immensely progressed over the past two decades, but integrated on-chip THz circuits and systems are still under development. This thesis is an effort to propose an integrated THz system by trapping a generated photocurrent THz wave and its coupling to the waveguide for on-chip propagation and processing. The proposed system consists of three parts; an optically-excited photoconductive THz source based on low-temperature grown (LT)-GaAs, a photonic crystal nanobeam cavity for THz wave confinement, and its coupling to a waveguide, both are based on a silicon platform. The thesis first investigates how the THz signal is generated by the photomixing techniques. It presents an analytical model to calculate the time-varying photocurrent acting as a THz source. Considering the THz dipole current exciting a cavity, I propose a photonic crystal nanobeam cavity inside a waveguide with high quality factor to confine the THz wave. The design and simulation of such a cavity are presented where the THz field mode has been found in a single-mode regime. Finally, the cavity is coupled to the waveguide using a tapering technique in the photonic crystal structure for efficient coupling and subsequent propagation by modal field matching. The proposed structure exhibits potential applications for integrated THz sources for various on-chip applications such as sensing, spectroscopy, and signal processing

Biomechanical assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study

AbstractBackgroundIntramedullary nails are the primary choice for treating long bone fractures. However, complications following nail surgery including non-union, delayed union, and fracture of the bone or the implant still exist. Reducing nail stiffness while still maintaining sufficient stability seems to be the ideal solution to overcome the abovementioned complications.MethodsIn this study, a new hybrid concept for nails made of carbon fibers/flax/epoxy was developed in order to reduce stress shielding. The mechanical performance of this new implant in terms of fracture stability and load sharing was assessed using a comprehensive non-linear FE model. This model considers several mechanical factors in nine fracture configurations at immediately post-operative, and in the healed bone stages.ResultsPost-operative results showed that the hybrid composite nail increases the average normal force at the fracture site by 319.23N (P<0.05), and the mean stress in the vicinity of fracture by 2.11MPa (P<0.05) at 45% gait cycle, while only 0.33mm and 0.39mm (P<0.05) increases in the fracture opening and the fragments' shear movement were observed. The healed bone results revealed that implantation of the titanium nail caused 20.2% reduction in bone stiffness, while the composite nail lowered the stiffness by 11.8% as compared to an intact femur.InterpretationOur results suggest that the composite nail can provide a preferred mechanical environment for healing, particularly in transverse shaft fractures. This may help bioengineers better understand the biomechanics of fracture healing, and aid in the design of effective implants

A smart load-speed sensitive cooling map to have a high- performance thermal management system in an internal combustion engine

Considering the fact that electrification is increasingly used in internal combustion engines, this paper aims at presenting a smart speed-load sensitive cooling map for better thermal management. For this purpose, first, thermal boundary conditions for the engine cooling passage were obtained by thermodynamic and combustion simulation. Next, the temperature distribution of the cooling passage walls was determined using conjugate heat transfer method. Then, the effect of engine load on wall temperature distribution was investigated, and it was observed that in the conventional mode where the cooling flow is only affected by the engine speed, the engine is faced with over-cooling and under-cooling. Therefore, the optimum flow for cooling the engine was achieved in such a way that the engine is hot enough and kept free from damage, while the engine has a more uniform temperature distribution. These calculations were performed by considering the boiling phenomenon. The results showed using the cooling map leads to a significant reduction in coolant flow, which in turn reduces the power consumption of the water pump and size of the radiator. Moreover, fuel consumption, hydrocarbon emission production, and the needed power of the coolant pump are enhanced by 2.1, 8.6, and 44.3%, respectively.Irankhodro Powertrain Company (IPCo)http://www.elsevier.com/locate/energy2022-04-22hj2021Mechanical and Aeronautical Engineerin

Optimisation of composite bone plates for ulnar transverse fractures

Metallic bone plates are commonly used for arm bone fractures where conservative treatment (casts) cannot provide adequate support and compression at the fracture site. These plates, made of stainless steel or titanium alloys, tend to shield stress transfer at the fracture site and delay the bone healing rate. This study investigates the feasibility of adopting advanced composite materials to overcome stress shielding effects by optimising the geometry and mechanical properties of the plate to match more closely to the bone. An ulnar transverse fracture is characterised and finite element techniques are employed to investigate the feasibility of a composite-plated fractured bone construct over a stainless steel equivalent. Numerical models of intact and fractured bones are analysed and the mechanical behaviour is found to agree with experimental data. The mechanical properties are tailored to produce an optimised composite plate, offering a 25% reduction in length and a 70% reduction in mass. The optimised design may help to reduce stress shielding and increase bone healing rates

BAZAAR : The Odyssey of the North

Since mid-20th century, the idea of having a holiday home outside of city has become increasingly popular among urban dwellers. The desire to escape the pollution, crowd, and stress of urban life, along with low prices of rural lands, increased urban income, higher levels of mobility, and the nostalgia for countryside are the main reasons behind the ownership of such properties. The development of this type of housing has many immediate advantages and disadvantages for the local community, which will be discussed in this paper in depth. However, the main intention is to find an unprecedented typology in these areas in order to establish a stable relationship between the locals and newcomers. To do so, I will concentrate on a holiday area in northern Iran and after analysis of the local climate, economy, culture, and architecture, I would address the issue of rapid development in this area across three different scales of inquiry and design: consideration of code of practice that acknowledges the pressures of new settlement while ensuring the legacy of historical practice, consideration of unprecedented building types that may arise, and consideration of how the new settlement and its unprecedented communal structures find their resolution in material culture.Applied Science, Faculty ofArchitecture and Landscape Architecture (SALA), School ofUnreviewedGraduat

Histopathologic Evaluation of Follicular Tissues Associated with Impacted Third Molars

Objective: The aim of the present study was to histopathologically evaluate follicular tissues of third molars with pericoronal radiolucenciesof less than 2 millimeters.Materials and Methods: In this descriptive analytic study, 100 impacted third molars with normal follicular spaces were removed and their pericoronaltissues submitted for histopathologic examination. Different characteristicsof the epithelium and connective tissue were evaluated in all cases. Statisti-cal analysis was performed using chi square and Mann-Whitney tests.Results: In our study sample, 74% of the patients were female and 26% were male, ranging in age from 13 to 54 years (mean, 25.3 years). Lining epithelium was observed in 69% of the specimens of which 31%, 23% and 14% was cuboidal, squamous and columnar, respectively. A significant re-lationship was found between the presence of squamous epithelium and pa-tient age (P<0.05). Nonspecific chronic inflammation was the only patho-logic finding observed in 44% of the specimens. Inflammation was signifi-cantly associated with age and squamous metaplasia (P<0.05).Conclusion: Considering that pathologic lesions were not observed in anyof the studied cases, unerupted third molars should not be removed unless there is a clinical indication to do so, or in case the impacted molar shows evidence of pathological changes. Follow-up is suggested for asympto-matic impacted third molars

Machine learning prediction approach for dynamic performance modeling of an enhanced solar still desalination system

An enhanced design for a solar still desalination system which has been proposed in the previously conducted study of the research team is considered here, and the experimental data obtained during a year are employed to develop ANN models for that. Different types of artificial neural network (ANN), as one of the most popular machine learning approaches, are developed and compared together to find the best of them to predict the hourly produced distillate and water temperature in the basin, which are two key performance criteria of the system. Feedforward (FF), backpropagation (BP), and radial basis function (RBF) types of ANN are examined. According to the results, by having the coefficients of determination of 0.963111 and 0.977057, FF and RBF types are the best ANN structures for estimation of the hourly water production and water temperature in the basin, respectively. In addition, the annual error analysis done for the data not used to develop ANN models demonstrates that the average error in prediction of the hourly distillate production and water temperature in the basin varies from 9.03 and 5.13% in January (the highest values) to 4.06 and 2.07% in July (the lowest values), respectively. Moreover, the error for prediction of the daily water production is in the range of 2.41 to 5.84% in the year.http://link.springer.com/journal/109732022-04-13hj2021Mechanical and Aeronautical Engineerin