This thesis presents the results of an experimental, numerical and analytical study to develop a design method to calculate shear resistance of flanged ferrocement beams with vertical mesh reinforcements in the web. Two groups of full-scale testing were conducted comprising of three I beams and four U beams. The I beams had the same geometry and reinforcement arrangements, but differed in the matrix strength or shear span to depth ratio. The U beams differed in web and flange thickness, reinforcement arrangements, matrix strength and shear span to depth ratio. The experimental data were used for validation of finite element models which had been developed using the ABAQUS software. The validated models were subsequently employed to conduct a comprehensive parametric study to investigate the effects of a number of design parameters, including the effect of matrix strength, shear span to depth ratio, cross sectional area, length of clear span, volume fraction of meshes and amount of rebar. The main conclusion from the experiments and parametric studies were: shear failure may occur only when the shear span to depth ratio is smaller than 1.5; the shear strength may increase by increasing the matrix strength, volume fraction of meshes, cross sectional area and amount of rebar. The main type of shear failure for I beams was diagonal splitting while for U beams it was shear flexural. Based on the results from the experimental and numerical studies, a shear design guide for ferrocement beams was developed. A set of empirical equations for the two different failure types and an improved strut-and-tie were proposed. By comparison with the procedures currently in practice, it is demonstrated that the methodology proposed in this thesis is likely to give much better predictions for shear capacity of flanged ferrocement beams.

Semi-conductor industry relies heavily on silicon (Si). However, Si is not a direct-band gap semi-conductor. Consequently, Si does not possess great versatility for multi-functional applications in comparison with the direct band-gap III-V semi-conductors such as GaAs. To bridge this gap, what is ideally required is a semi-conductor material system that is based on silicon, but has significantly greater versatility. While sparsely studied, the semi-conducting silicides material systems offer great potential. Thus, I focused on the growth and structural characterization of ruthenium silicide and osmium silicide material systems. I also characterized iron silicon germanide films using extended x-ray absorption fine structure (EXAFS) to reveal phase, semi-conducting behavior, and to calculate nearest neighbor distances. The choice of these silicides material systems was due to their theoretically predicted and/or experimentally reported direct band gaps. However, the challenge was the existence of more than one stable phase/stoichiometric ratio of these materials. In order to possess the greatest control over the growth process, molecular beam epitaxy (MBE) has been employed. Structural and film quality comparisons of as-grown versus annealed films of ruthenium silicide are presented. Structural characterization and film quality of MBE grown ruthenium silicide and osmium silicide films via in situ and ex situ techniques have been done using reflection high energy electron diffraction, scanning tunneling microscopy, atomic force microscopy, cross-sectional scanning electron microscopy, x-ray photoelectron spectroscopy, and micro Raman spectroscopy. This is the first attempt, to the best of our knowledge, to grow osmium silicide thin films on Si(100) via the template method and compare it with the regular MBE growth method. The pros and cons of using the MBE template method for osmium silicide growth are discussed, as well as the structural differences of the as-grown versus annealed films. Future perspectives include further studies on other semi-conducting silicides material systems in terms of growth optimization and characterization.

III-Nitride materials, which consist of AlN, GaN, InN, and their alloys have become the cornerstone of the third generation compound semiconductor. Planar IIINitride materials are commonly grown on sapphire substrates which impose several limitations such as challenging scalability, rigid substrate, and thermal and lattice mismatch between substrate and material. Semiconductor nanowires can help circumvent this problem because of their inherent capability to relieve strain and grow threading dislocation-free without strict lattice matching requirements, enabling growth on unconventional substrates. This thesis aims to investigate the microscopic characteristics of the nanowires and expand on the possibility of using transparent amorphous substrate for III-nitride nanowire devices. In this work, we performed material growth, characterization, and device fabrication of III-nitride nanowires grown using molecular beam epitaxy on unconventional substrates. We first studied the structural imperfections within quantum-disks-in-nanowire structure grown on silicon and discovered how growth condition could affect the macroscopic photoluminescence behavior of nanowires ensemble. To expand our work on unconventional substrates, we also used an amorphous silica-based substrate as a more economical substrate for our nanowire growth. One of the limitations of growing nanowires on an insulating substrate is the added fabrication complexity required to fabricate a working device. Therefore, we attempted to overcome this limitation by 5 investigating various possible GaN nanowire nucleation layers, which exhibits both transparency and conductivity. We employed various nucleation layers, including a thin TiN/Ti layer, indium tin oxide (ITO), and Ti3C2 MXene. The structural, electrical, and optical characterizations of nanowires grown on different nucleation layers are discussed. From our work, we have established several key processes for transparent nanowire device applications. A nanowire LED emitting at ∼590 nm utilizing TiN/Ti interlayer is presented. We have also established the growth process for n-doped GaN nanowires grown on ITO and Ti3C2 MXene with transmittance above 40 % in the visible wavelength, which is useful for practical applications. This work paves the way for future devices utilizing low-cost substrates, enabling further cost reduction in III-nitride device fabrication.

Thesis (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Orthodontics and Dentofacial Orthopedics). / Includes bibliographic references: leaves 37-42. / Background: Craniofacial skeletal asymmetry is a common finding in the general population that often goes undetected. Interest in this topic has led to many studies aimed at describing this type of asymmetry, its distribution and etioIogy. The cranial base, being cIosely related to the face and brain, is a key component in craniofacial growth and may also display varying amounts of asymmetry contributing to this anomaly. Though many studies have explored underlying skeletal asymmetry, most of them were limited by their two-dimensional method of investigation. With the advent of three-dimensional technology, more recent studies have had the advantage of studying the cranial base in its true anatomic form, resulting in greater accuracy of analysis. Despite access to this technoIogy, there is still a lack of literature regarding the cranial base in a normal population. Determining average skull base dimensions will provide a set of normative data that can be used as a reference for future studies. Material and Methods: Pre-treatment Cone Beam Computed Tomography (CBCT) films of 160 esthetic human subjects previously used by another investigator were screened for use in our current research. These DICOM files were imported into InVivoDental5.3 software (Anatomage[TM]; San Jose, Calif.) for screening and 70 CBCT scans were selected for analysis. All patients were classified as cervical vertebral stage 4 and above. The images were oriented in all three planes of space for uniformity and 14 bilateral anatomic landmarks were identified on each scan. A mid-sagittal reference plane was created using crista galli as the origin, and extending a perpendicular passing through the middle of the right and left clinoid points connected by a line, and through posterior points basion and opisthion. Each landmark was given an x-, y- and z- coordinate representing its three dimensional position and bilateral linear measurements to the reference plane were recorded using the software system. Statistical Analysis: InVivoDental5.3 software was used to calculate linear distances between each landmark and the mid-sagittal plane. This data was exported into Microsoft excel for analysis. Descriptive statistics of our sample and paired t-tests with a 5% significance level, or p value of 0.05, were performed. Results: The means of the right and left measurements of each bilateral landmark were calculated along with their standard deviations. A comparison between right and left means was accomplished with the use of paired t-tests. 12 1andmarks did not show a statistical difference in their locations on either side of the mid-sagittal plane. However, the means of 2 landmarks were found to be statistically significant. These were euryon (p = 0.01) and the jugular foramen (p = 0.00) Conclusion: The overall trend of our data indicated that the cranial base in a normal population, without craniofacial anomaly, displays symmetry, with the exception of the location of euryon and the jugular foramen. These findings are in accordance with those of similar three-dimensional studies. It is likely that the significant findings were due to tracing error, given the indiscrete location of euryon and the large, relatively asymmetric shape of the jugular foramen. However, if these structures are truly asymmetric, we can infer from our sample of symmetric patients, that there is no clinical relevance. Further studies with an increased sample size, additional landmarks or a more discrete sample can be performed to continue describing the skull base. The results of this study offer valuable reference data that can be used as a baseline for future studies.

A novel source of hyperthermal (1-30 eV) reactive neutrals based on the surface-reflection-neutralization technique is described. This source is potentially capable of minimizing the charge-induced damage associated with plasma based semiconductor processing steps. The goal of this thesis is to investigate the issues involved in scale-up of this technology for processing of 8{dollar}\sp{lcub}\prime\prime{rcub}{dollar} diameter wafers used today in the semiconductor industry. This includes modeling the plasma ion source and trajectory simulations of the reflected neutral flux. A prototype source was constructed for experimental verification of the plasma model.;An inductively coupled plasma (ICP) source is used to provide a source of reactive ions. These ions are neutralized and reflected through interaction with a biased metal plate. These reflected neutrals are directed at a wafer to be etched (for feature delineation) or cleaned (removal of etch residue).;The plasma source is modeled with a global (volume averaged) power deposition model to determine plasma densities at the reflector plate. The modeled values are compared to measurements of a prototype neutral stream source. Plasma parameter measurements are carried out using Langmuir single probes. It is found that the plasma densities in the upstream plasma source and at the reflector plate agree well (within 10%) with the model.;Several models of reflected neutral trajectories are used to determine the final flux characteristics at the wafer. 2-D and 3-D ray trace trajectory models were used, as well as a full 3-D Monte Carlo treatment. It is found that in geometry considered in this work, background pressure plays a key role in delivering hyperthermal neutrals to the wafer. Energy and angular distributions are altered severely as the neutrals traverse the background gas and plasma.

The search for alternative methods of synthesizing cubic boron nitride (cBN), one of the hardest known materials, at low thermo-baric conditions has stimulated considerable research interest due to its great potential for numerous practical industrial applications. The practical applications are motivated by the material’s amazing combination of extraordinarily superior properties. The cBN phase is presently being synthesized from graphite-like boron nitride modifications at high thermo-baric conditions in the presence of catalytic solvents or by ion–beam assisted (chemical and physical) deposition methods. However, the potential and performance of cBN have not been fully realized largely due to central problems arising from the aforementioned synthesis methods. The work reported in this dissertation is inspired by the extensive theoretical investigation of the influence of defects in a ecting the transformation of the hexagonal boron nitride (hBN) phase to the cBN phase that was carried out by Mosuang and Lowther (Phys Rev B 66, 014112 (2002)). From their investigation, using an ab-initio local density approach, for the B, C, N, and O simple defects in hBN, they concluded that the defects introduced into hBN could facilitate a low activation–energy hexagonal-to-cubic boron nitride phase transformation, under less extreme conditions. We use ion implantation as a technique of choice for introducing ‘controlled’ defects into the hot–pressed polycrystalline 99.9% hBN powder samples. The reasons are that the technique is non–equilibrium (not influenced by dilusion laws) and controllable, that is the species of ions, their energy and number introduced per unit area can be changed and monitored easily. We investigate the structural modifications of hBN by ion implantation. Emphasis is given to the possibilities of influencing a low activation–energy hBN-to-cBN phase transformation. The characterization of the structural modifications induced to the hBN samples by implanting with He+ ions of energies ranging between 200 keV and 1.2 MeV, at fluences of up to 1.0 1017 ionscm2, was accomplished by correlating results from X-Ray Di raction (XRD), micro-Raman (-Raman) spectroscopy measurements, and two-dimensional X-Y Raman (2D-Raman) mapping measurements. The surface to pography of the samples was investigated using Scanning Electron Microscopy (SEM). E orts to use Surface Brillouin Scattering (SBS) were hampered by the transparency of the samples to the laser light as well as the large degree of surface roughness. All the implantations were carried out at room temperature under high vacuum. 2D-Raman mapping and -Raman spectroscopy measurements done before and after He+ ion irradiation show that an induced hBN-to-cBN phase transformation is possible: nanocrystals of cBN have been observed to have nucleated as a consequence of ion implantation,the extent of which is dictated by the fluences of implantation. The deviationof the measured spectra from the Raman spectra of single crystal cBN is expected, has been observed before and been attributed to phonon confinement e ects. Also observed are phase transformations from the pre-existing hBN modification to: (a) the amorphous boron nitride (aBN), (b) the rhombohedral boron nitride (rBN) modifications, (c) crystalline and amorphous boron clusters, which are a result of the agglomeration of elementary boron during and immediately after ion implantation. These transformations were observed at high energies. Unfortunately, the XRD measurements carried out could not complement the Raman spectroscopy outcomes probably because the respective amounts of the transformed materials were well below the detection limit of the instrument used in the former case.

<p>Millimeter-wave communications use narrow beams to overcome the enormous signal attenuation. Such narrow-beam communication demands precise beam-alignment between transmitter and receiver and may entail huge overhead, especially in high mobility scenarios. Moreover, detection of the optimal beam is challenging in the presence of beam imperfections and system noise. This thesis addresses the challenges in the design of beam-training and data-communication by proposing various schemes that exploit different timescales. On a short timescale, we leverage the feedback from the receiver to efficiently perform beam-training and data-communication. To this end, we have worked in three different areas. In the first research direction, we design an optimal interactive beam-training and data-communication protocol, with the goal of minimizing power consumption under a minimum rate constraint. The optimality of a fixed-length beam-training phase followed by a data-communication phase is proved under the assumption of perfect binary feedback. In the second research direction, we propose a coded energy-efficient beam-training scheme, robust against the feedback/detection errors. In the third research direction, we investigate the design of the beam-training in the presence of uncertainty due to noise and beam imperfections. Based on the bounding of value-function, the second-best preference policy is proposed, which achieves a promising exploration-exploitation tradeoff. On the other hand, on longer timescales, we exploit the mobility and blockage dynamics and beam-training feedback to design throughput-efficient beam-training and data-communication. We propose a point-based value iteration (PBVI) algorithm to determine an approximately optimal policy. However, the design relies on the a-priori knowledge of the state dynamics, which may not be available in practice. To address this, we propose a dual timescale approach, where on the long timescale, a recurrent deep variational autoencoder (R-VAE) uses noisy beam-training observations to learna probabilistic model of system dynamics; on the short timescale, an adaptive beam-training procedure is optimized using PBVI based on beam-training feedback and a probabilistic knowledge of the UE's position provided by the R-VAE. In turn, the observations collected during the beam-training procedure are used to refine the R-VAE via stochastic gradient descent in a continuous process of learning and adaptation.<br></p>

Multiport beam splitter is a new research topic in quantum communication. To improve the security system, the dimension/capacity of quantum communication should increase. In this thesis, design, simulation and methodology of NXN multiport beam splitter on a photonic integrated circuit is explained. Photonic integrated circuit has more advantages than other optical components to design a multiport beam splitter. Multiport beam splitter on a photonic chip gives configuration stability, a compact prototype for future quantum network.

archives@tulane.edu / A cold molecular beam approach has been pioneered to investigate the pyrolysis reactions of triglycerides (TGs) as a function of temperature. Traditionally, an established repertoire of laser techniques is utilized for multiple species present, which has been extensively used for a detailed study of specifically targeted species that are often novel and reactive. Instead, we have applied these methods for the mass characterization of numerous product species as they appeared. Unlike traditional batch reactor studies of pyrolysis, where terminal products are identified and characterized generally using GC/MS methods, herein, product analysis was conducted in real time. Experiments were performed by recording mass spectra as a function of increasing sample temperature. For clearer results and interpretation, most studies employed model TGs containing a single fatty acid, such as oleic or stearic acid. Soft photoionization was conducted using 118 and 266 nm laser-based pulses. Time-of-flight mass spectroscopy (TOF-MS) was conducted after each photoionization pulse. Several novel direct observations include 1) the observation of initial cracking temperatures and the formation of non-aromatic and aromatic products; 2) the determination of key factors for pyrolysis—fatty acid detachment from the glycerol backbone and subsequent fatty acid pyrolysis; 3) the growth of C6 and C7 fragments as an important precursor for following association reactions. The use of 266 nm pulses exclusively facilitated the sensitive and selective photoionization of aromatic products and, thus, the thorough examination of the evolving aromatic products. Unlike the batch reactor studies of terminal products, the molecular beam studies of aromatic products revealed the evolution to a small number of selective and relatively massive polycyclic aromatic hydrocarbons (PAH). It is deduced that in a batch reactor, these undetected products ultimately lead to solids and tars that are difficult to analyze. Our investigation revealed that hydrogen addition showed some effectiveness in inhibiting formation of large / 1 / Ibrahi M. Alhroob

A recurring theme in my research is that mathematical matrix methods may be used in a wide variety of physics and engineering applications. Transfer matrix techniques are conceptually and mathematically simple, and they encourage a systems approach. Once one is familiar with one transfer matrix method, it is straightforward to learn another, even if it is from a completely different branch of science. Thus it is useful to overview these methods, and this has been done here. Of special interest are the applications of these methods to laser optics, and matrix theorems concerning multipass optical systems and periodic optical systems have been generalized here to include, for example, the effect of misalignment on the performance of an optical system. In addition, a transfer matrix technique known as generalized beam method has been derived to treat misalignment effects in complex optical systems. Previous theories used numerical or ad hoc analytical solutions to a complicated diffraction integral. The generalized beam matrix formalism was also extended to higher-order beam modes of lasers and used to study mode discrimination in lasers with misaligned complex optical elements.