Omniphobic surfaces, which repel polar and non-polar liquids alike, have proven of value in a myriad of applications ranging from piping networks, textiles, food and electronics packaging, and underwater drag reduction. A limitation of currently employed omniphobic surfaces is their reliance on perfluorinated coatings/chemicals, increasing cost and environmental impact and preventing applications in harsh environments. Thus, there is a keen interest in rendering conventional materials, such as hydrocarbon-based plastics, omniphobic by micro/ nanotexturing rather than via chemical makeup, with notable success having been achieved for silica surfaces with doubly reentrant pillars (DRPs). We discovered a critical limitation of DRPs – they catastrophically lose superomniphobicity in the presence of localized physical damages/defects or on immersion in wetting liquids. In response, we pioneered bio-inspired gas-entrapping microtextured surfaces (GEMS) architecture composed of doubly reentrant cavities (DRCs). DRCs are capable of robustly entrapping air when brought into contact with liquid droplets or on immersion, which prevents catastrophic wetting transitions even in the presence of localized structural damage/defects. This dissertation presents our multifaceted research on DRCs via custom-built pressure cells, confocal laser scanning microscopy, environmental scanning electron microscopy, contact angle goniometry, high-speed imaging, and upright optical microscopy. Specific accomplishments detailed in this thesis include: (i) the microfabrication protocols for silica GEMS developed at KAUST; (ii) the characterization of GEMS’ omniphobicity via apparent contact angles and immersion; (iii) the demonstration of ~ 1000,000,000% delays in wetting transitions in DRCs compared to those in simple cavities (SCs) under hexadecane; (iv) a proposal for immersion of surfaces as a criterion for assessing their omniphobicity in addition to apparent contact angles; (v) effects of surface chemistry, hydrostatic pressure, and cavity dimensions on Cassie-to-Wenzel transitions in DRCs and SCs; (vi) the demonstration of “breathing” (liquid-vapor) interfaces in GEMS under fluctuating hydrostatic pressures; and (vii) the demonstration of directional wetting transitions in DRCs (or cavities in general) arranged in one- and two-dimensional lattices. The last chapter in the thesis presents future research directions such as breathing surfaces capable of preempting vapor condensation and gas replenishment.

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Vid användning av Virtual Reality (VR) fanns en stor nackdel; Användare kunde inte utföra fullt rörelseomfång, framför allt förflyttning av olika slag; promenad, löpning, hopp samt sidosteg och gång baklänges. Användare förblev begränsade till utrymmets area och luft-rum. Antingen var användaren tvungen att strukturera om sitt utrymme eller så anpassades själva VR-programmet och dess headset för att kunna tillgodose detta problem på mest optimala sätt. Det har uppstått olika koncept av löpband som är inriktade för VR med syftet att lösa denna begränsning. Däremot var dessa koncept inte tillräckligt effektiva i att översätta normalt rörelsemönster till VR. Syftet med detta projekt var att vidareutveckla de etablerade koncepten med målet att ta reda på om en helt ny koncept-idé kunde fungera optimalt. Resultaten visade på att koncept-idén har potential men fortsatt arbete i en större omfattning skulle vara nödvändigt. / When using Virtual Reality (VR) there was a major drawback; Users could not perform full range of motion, especially locomotion of various kinds; walking, running, jumping as well as side steps and walking backwards. Users remained limited to the space's area and airspace. Either the user had to restructure their space or the VR-program itself and its headset were adapted to accommodate this problem in the most optimal way. Various treadmill concepts have emerged that are geared for VR with the aim of solving this limitation. However, these concepts were not effective enough in translating normal movement pattern to VR. The purpose of this project was to further develop the established concepts with the goal of finding out if a completely new concept idea could work optimally. The results showed that the concept idea has potential but continued work on a larger scale would be necessary.

An important aspect of wireless networks is their dynamic behavior. The conventional protocol stack is inflexible as various protocol layers communicate in a strict manner. In such a case the layers are designed to operate under the worst conditions as opposed to adapting to changing conditions. This leads to inefficient use of spectrum and energy. Adaptation represents the ability of network protocols and applications to observe and respond to channel conditions. Traditional simulation methodologies independently model the physical and higher layers. When multiple layer simulations are required, an abstraction of one layer is inserted into the other to provide the multiple layer simulation. However, recent advances in wireless communication technologies, such as adaptive modulation and adaptive antenna algorithms, demand a cross layer perspective to this problem in order to provide a sufficient level of fidelity. However, a full simulation of both layers often results in excessively burdensome simulation run-times. The benefits and possible parametric characterization issues arising due to the cross-layer integration of lower physical and higher network layers are investigated in this thesis. The primary objective of investigating cross-layer simulation techniques is to increase the fidelity of cross-layer network simulations while minimizing the simulation runtime penalties. As a study of cross-layer system design a medium access control (MAC) scheme is studied for a MANET wherein the nodes are equipped with smart antennas. Traditional MAC protocols assume the use of omnidirectional antennas. Nodes with directional antennas are capable of transmitting in certain directions only and significantly reduce the chances of collision and increase the effective network capacity. MANETs using omni-directional antennas severely limit system performance as the entire space around a node up to its radio range is seen as a single logical channel. In this research a MAC protocol is studied that exploits space division multiple access at the physical layer. This is a strong example where physical and MAC design must be carried out simultaneously for adequate system performance. Power control is a very important in the design of cellular CDMA systems which suffer from the near-far problem. Finally, the interaction between successive interference cancellation (SIC) receivers at the physical layer and power control, which is a layer 2 radio resource management issue, is studied. Traffic for future wireless networks is expected to be a mix of real-time traffic such as voice, multimedia teleconferencing, and games and data traffic such as web browsing, messaging, etc. All these applications will require very diverse quality of service guarantees. A power control algorithm is studied, which drives the average received powers to those required, based on the QoS requirements of the individual users for a cellular CDMA system using SIC receivers. / Master of Science

This research is the first systematic investigation of solid-state orientation as a novel method for controlling drug release from biodegradable polymers. The effect of various degrees of polymer orientation was studied in oriented Poly (L-lactic acid) (PLA) films containing curcumin and theophylline as model drugs. Additionally, direction specific drug release was studied from oriented PLA rods containing paracetamol. The films oriented to 2X uniaxial constant width (UCW) or 2X2Y biaxial draw ratio showed retardation of drug release, when their nematic structure was stabilised by the presence of crystalline theophylline. Contrarily, the same films when contained solid solution of curcumin, shrunk in the release medium and exhibited a release profile similar to the un-oriented films. All films oriented to the UCW draw ratio ≥ 3X contained α crystalline form of PLA and showed acceleration of drug release proportionate to the draw ratio. According to the proposed mechanism augmented formation of water filled channels in these films was responsible for faster drug release. Similarly, the paracetamol loaded PLA rods die-drawn to uniaxial draw ratios ≥ 3X exhibited enhancement of drug release. Importantly, the amount of drug released along the oriented chain axis was significantly larger than that in the perpendicular direction. Drug release from the die-drawn rods was accelerated by a greater degree than that observed from the oriented films. This can be correlated to the differences in their size, geometry and the crystalline form of PLA. In conclusion, the current study provided substantial evidence that solid-state orientation can offer a control over drug release from PLA.

Yes / The purpose of this study is to determine whether Indian banks were able to weather the COVID-19 storm. We estimate banks’ deposits-generating and operating efficiencies using a two-stage directional distance function-based network data envelopment analysis (DDF- NDEA) approach and seek to capture the immediate impact of COVID-19 on these efficiency measures by comparing their magnitudes in the pre-pandemic (2014/15-2019/20), just 1-year prior to the pandemic (2019/20), and during the pandemic year (2020/21) periods. The study looks at whether the impact of the COVID-19 pandemic was uniform across ownership types and size classes. The empirical findings suggest that the Indian banking system was resilient and withstood the immediate impact of the COVID-19 pandemic. During the study period, however, the large and medium-sized banks experienced some effi ciency losses. By and large, regardless of bank group, banks have shown resilience to the shock of the global health pandemic and improvements in efficiency. / The full-text of this article will be released for public view at the end of the publisher embargo on 28 Dec 2024.

Directional couplers are passive components in radio frequency (RF) engineering and have a broad set of applications. With the scope of how a directional coupler can be implemented in a design, it is important to have specified goals in mind when designing a coupler, for the component to be precise and behave in a desired way. Different design variations also have benefits and disadvantages, and in this project several variations of couplers were investigated. The limiting factors in this project were the rather small area to work with, combined with the design requirements. This is ultimately what made the design approach unique and the reason for using an iterative process in a simulation software, where conventional methods of designing could not be used. Out of the different designs that were tested, two directional couplers on the RO4350B substrate with a gap of 0.34 mm between the transmission lines fulfilled every design parameter except the one regarding the coupling factor. There are three notable conclusions that were drawn. The first is that all directivity compensation methods that were evaluated are valid after optimizing relevant parameters. Some methods could be combined to have an even greater effect, such as the soldermask and wiggly line methods. The second is that ground vias can affect the directivity of a directional coupler substantially. Designing a coplanar waveguide coupler can also have benefits in respect to the given design requirements in this project. Thirdly, a lossy material such as FR4 could be used and still achieve the design parameters at these frequencies.