Silicon nanocavity light emitters at 1.3-1.5 µm wavelength

Silicon Photonics has been a major success story in the last decade, with many photonic devices having been successfully demonstrated. The only missing component is the light source, however, as making an efficient light source in silicon is challenging due to the material’s indirect bandgap. The development of a silicon light source would enable us to make an all-silicon chip, which would find many practical applications. The most notable among these applications are on-chip communications and sensing applications. In this PhD project, I have worked on enhancing silicon light emission by combining material processing and device engineering methods. Regarding materials processing, the emission level was increased by taking three routes. In all the three cases the emission was further enhanced by coupling it with a photonic crystal (PhC) cavity via Purcell effect. The three different approaches taken in this PhD project are listed below. 1. The first approach involves incorporation of optically active defects into the silicon lattice by hydrogen plasma treatment or ion implantation. This process results in broad luminescence bands centered at 1300 and 1500 nm. By coupling these emission bands with the photonic crystal cavity, I was able to demonstrate a narrowband silicon light emitting diode at room temperature. This silicon nano light emitting diode has a tunable emission line in the 1300-1600 nm range. 2. In the second approach, a narrow emission line at 1.28µm was created by carbon ion implantation, termed “G-line” emission. The possibility of enhancing the emission intensity of this line via the Purcell effect was investigated, but only with limited success. Different proposals for future work are presented in this regard. 3. The third approach is deposition of a thin film of an erbium disilicate on top of a PhC cavity. The erbium emission is enhanced by the PhC cavity. Using this method, an optically pumped light source emitting at 1.54 µm and operating at room temperature is demonstrated. A practical application of silicon light source developed in this project in gas sensing is also demonstrated. As a first step, I show refractive index sensing, which is a simple application for our source and demonstrates its capabilities, especially relating to the lack of fiber coupling schemes. I also discuss several proposals for extending applications into on-chip biological sensing

Preoperative Factors Associated with Weight Loss Following Bariatric Surgery

Obesity is a major health issue in the United States. More than two thirds of the adult population is considered to be either overweight or obese. It is the fifth leading cause of mortality in the world, with 3.4 million deaths a year. Obesity is associated with numerous medical and psychological comorbidities. There are various types of treatments for obesity, such as diets, exercise and pharmacological agents; however, bariatric surgery is one of the most effective and proven treatments for morbidly obese patients. Although the bariatric surgery success rates are high, up to 30% percent of individuals do not achieve successful weight loss after surgery. The major predictors of weight loss success for bariatric surgery are often dependent on presurgical variables. This study investigated five preoperative variables associated with weight loss following bariatric surgery: overeating behaviors, cravings, social isolation, affect disturbance, and preoperative weight loss. No significant differences were found, but the results were congruent with previous findings that an individual’s age and BMI were negatively correlated with successful postoperative weight loss. Recommendations for future studies are provided to explore the importance of preoperative factors in long-term success following bariatric surgery

Some Results for the Drazin Inverses of the Sum of Two Matrices and Some Block Matrices

We give a formula of (P+Q)D under the conditions P2Q+QPQ=0, P3Q=0, and PQPQ=0. Then, we apply it to give some expressions for the Drazin inverse of block matrix M=(ABCD) (A and D are square matrices) under some conditions, generalizing some recent results in the literature. Finally, numerical examples are given to illustrate our results

Talc as a nucleating agent and reinforcing filler in poly(lactic acid) composites

The effect of talc on the crystallinity and mechanical properties of a series of poly(lactic acid) (PLA)/talc composites has been investigated. The composites were prepared by melt blending followed by compression molding. It was found that talc acted as a nucleating agent and increased the crystallinity of the PLA from 2% to 25%. There was significant improvement in Young's modulus of the composites with increasing talc addition and these results were found to fit the Halpin Tsai model. Thermo-mechanical tests confirmed that the combination of increased crystallinity and storage modulus leads to improvement in the heat distortion properties

A Density Functional Theory Study of Raman Modes of Hydrogenated Cadmium Sulphide Nanoparticles

Raman scattering investigations based on density functional theory (DFT) calculations were performed to explore the vibrational modes of wurtzite structured CdS nanoparticles (NPs). The calculations were performed to obtain the Raman spectra for the CdS containing 2, 4, 8 and 12 atoms to study the size dependence. Several vibrational modes indicating stretching and bending features related to Cd and S atoms were observed. Modifications of the frequency and intensity of different Raman modes with an increase in number of atoms in NPs are discussed in detail. It is found that the frequency of the CdS symmetric stretching mode of vibration shows a consistent red shift and that of CdS anti‐symmetric stretching shows a consistent blue shift with the increase in the number of atoms. Hydrogen atoms were added in order to make the closed shell configuration and saturate the NPs as per the requisite for calculating the Raman spectra. This produced some additional modes of vibration related to hydrogen atoms. The SH stretching mode showed a consistent red shift and the CdH stretching mode showed a consistent blue shift with an increase in the number of atoms in NPs. The results generated are found to be in close agreement with the literature. The observed red shift in different modes is assigned to stimulated Raman stretching and blue shift is ascribed to the coherent anti‐stokes Raman scattering

SMALL AND MEDIUM-SIZE ENTERPRISES IN PAKISTAN: DEFINITION AND CRITICAL ISSUES

SMEs play a vital role in the development of an economy. Thecontribution of Pakistani SMEs is less as compared to other countries, yet their significance cannot be denied. The SME sector is facing multifarious problems that made it difficult to contribute to the nation‘s GDP. This paper attempts to focus on the major constraints faced by the SMEs. The basic problem starts with no defined and standardized size for SMEs. The paper examines the definitions of SMEs given by different government organizations in Pakistan with some possible suggestion for one standard SME definition (in terms of size). This paper also highlights the critical issues of Pakistani SMEs such as financial, human, physical and technological. The paper concludes with some brief prospects by recommending a few implications for policy

Increased body mass index may lead to hyperferritinemia irrespective of body iron stores

Objective: Obesity causes subclinical inflammation which results in the secretion of various bioactive peptides that are key players in metabolic regulation of iron homeostasis. We sought to establish correlation of one such peptide (ferritin) with marker of subclinical inflammation (CRP) in various BMI.Methods: Total 150 subjects between the ages of 20-60 years were included in the cross-sectional study conducted at Basic Medical Sciences Institute, Jinnah Post Graduate Medical Centre, Karachi, Pakistan. Body Mass Index (BMI) was calculated by weight (kg) /height (m(2)). The given values were used as reference for Group A: normal weight (18.0-22.9 kg/m2), Group B: overweight (23.0-24.9 kg/m2), Group C: obese ( \u3e 25.0 kg/m2) according to South Asian criteria. Serum Iron, Total Iron Binding Capacity, serum Transferrin Saturation, serum Ferritin and C-reactive protein were measured by commercially available kits. ANNOVA with Tukey\u27s minimum significant difference and Spearman Rho correlation were used considering p \u3c 0.05 significant.Results: The results identified an increased serum Ferritin and CRP in obese versus lean subjects (p \u3c 0.001). BMI showed significantly positive correlation with serum CRP (r = 0.815; p-value \u3c 0.01) and Ferritin (r = 0.584; p-value \u3c 0.01). However, serum Iron levels and Transferrin saturation decreased in obese versus normal weight individuals (p \u3c 0.001).Conclusion: This integrated new data reveals that individuals with high BMI had high levels of Serum Ferritin despite low levels of iron with high levels of C- reactive protein. This might be caused due to inflammatory conditions prevailing in the presence of increased adipose tissue

The Alteration and Mineralization Characteristics of Miocene Porphyry Cu-Au Deposits of Chagai Magmatic Belt, District Chagai, Balochistan, Pakistan

Subduction related Miocene porphyry type deposits are found in the east-west trending Chagai magmatic belt (CMB) in Pakistan's western margin, Balochistan. This arc exists on the west segment of the Tethyan metallogenic belt in the south-west of Pakistan. Tethyan metallogenic belt is widely spread over 12,000 km from east to west direction from Indochina, Tibet, Pakistan, Iran, Turkey and Alpine mountain range in Europe. During the last thirty to forty years several porphyry deposits have been reported in the Chagai magmatic arc, including the very large Reko Diq H14-H15, large Saindak, Tanjeel, H35, H8 and medium Dasht-e-Kain porphyry deposits and many small porphyry copper deposits. These porphyry deposits were developed within the phase of calc-alkaline type magmatism in the Chagai arc. Tonalite, quartz diorite, and monzonite host the porphyry deposits within the adjacent sedimentary wall rock units of Sinjrani Volcanic Group, Juzzak, Saindak, and Amalaf Formations. The concentric zonal pattern of hydrothermal alteration in these porphyry deposits of the Chagai magmatic arc follows the world's major porphyry deposits' alteration pattern. Zones of hydrothermal alteration from distal to proximal part includesa potassic alteration, sericitic-clay-chlorite alteration, sericitic alteration, argillic alteration and propylitic alteration. Major ore mineralization in these deposits is of copper, gold, silver, molybdenum, and minor constituents of other base metals that have been reported to occur within hydrothermal alteration zones in the Miocene porphyry Chagai magmatic ar