A Multiscale Nonlocal Progressive Damage Model for Composite Materials

In this paper, the advantages of a nonlocal progressive damage formulation are described and demonstrated. An approximation of the nonlocal formulation was implemented coupled with the MAT162 composite damage model as a User defined material model in the LS DYNA environment. A comparison of the local model and the nonlocal model is simulated for an 8-ply laminate under tension is carried for increasing mesh densities. The results show the regularization achieved by nonlocal models by providing mesh independent results

Error Compensation in Pipeline and Converters

This thesis provides an improved calibration and compensation scheme for pipeline Analog-to-Digital Converters (ADCs). This new scheme utilizes the intermediate stage outputs in a pipeline to characterize error mechanisms in the architecture. The goal of this compensation scheme is to increase the dynamic range of the ADC. The pipeline architecture is described in general, and tailored to the 1.5 bitslstage topology. Dominant error mechanisms are defined and characterized for an arbitrary stage in the pipeline. These error mechanisms are modeled with basis functions. The traditional calibration scheme is modified and used to iteratively calculate the error characteristics. The information from calibration is used to compensate the ADC. The calibration and compensation scheme is demonstrated both in simulation and using a custom hardware pipeline ADC. A 10-bit 5 MHz ADC was designed and fabricated in 0.5 pm CMOS to serve as the demonstration platform. The scheme was successful in showing improvements in dynamic range while using intermediate stage outputs to efficiently model errors in a pipeline stage. An application of the technique on the real converter showed an average of 8.6 dB improvement in SFDR in the full Nyquist band of the ADC. The average improvement in SINAD and ENOB are 3.2 dB and 0.53 bits respectively

High Strain Rate Response of Adhesively Bonded Fiber-Reinforced Composite Joints A Computational Study to Guide Experimental Design

Adhesively bonded carbon fiber-reinforced epoxy composite laminates are widely used in aerospace applications. During a high energy impact event, these laminates are often subjected to high strain rate loading. However, the influence of high strain rate loading on the response of these composite joints is not well understood. Computational finite element (FE) modeling and simulations are conducted to guide the design of high strain rate experiments. Two different experimental designs based on split Hopkinson bar were numerically modeled to simulate Mode I and Mode II types loading in the composite. In addition, the computational approach adopted in this study helps in understanding the high strain rate response of adhesively bonded composite joints subjected to nominally Mode I and Mode II loading. The modeling approach consists of a ply-level 3D FE model, a progressive damage constitutive model for the composite material behavior and a cohesive tie-break contact element for interlaminar delamination

Genetic studies on a soil streptomyces sp. that produces an antifungal compoud

Master'sMASTER OF SCIENC

Alteration of physico-mechanical properties of black tilapia scale gelatins using UVA and UVC irradiation

Fish gelatin is abundant, relatively low cost and biodegradable. However, their inferior mechanical and rheological properties make them less competitive compared to mammalian gelatins. Hence, the effects of Ultraviolet (UV) irradiation on the properties of scale gelatins were analyzed. Gelatins were extracted from black tilapia scale via thermal extraction method. The gelatins were then subjected to Ultraviolet-A (UVA) and Ultraviolet-C (UVC) irradiation for 0.5 to 2.5 h and the changes in gel strength, viscosity, and melting temperature were observed. Results obtained show a marked increase in the gel strength and viscosity of the gelatins. However, the effects on the melting temperature are minimal. Treatment with UVA and UVC improved the gel strength of the gelatins up to 5.12 ± 0.22 N and 4.75 ± 0.09 N, respectively. Further analysis using Fourier Transform Infrared (FTIR) Spectroscopy showed crosslinking formation in the polypeptide chains induced by UV irradiation. UVA was found to be more effective in enhancing the properties of scale gelatins compared to UVC. In general, UV-irradiated scale gelatins showed excellent properties compared to the commercial bovine gelatin. Results indicated the prospects of employing UV treatment in enhancing the properties of fish gelatin

Alteration of Physico-mechanical Properties of Black Tilapia Scale Gelatins using UVA and UVC Irradiation

Fish gelatin is abundant, relatively low cost and biodegradable. However, their inferior mechanical and rheological properties make them less competitive compared to mammalian gelatins. Hence, the effects of Ultraviolet (UV) irradiation on the properties of scale gelatins were analyzed. Gelatins were extracted from black tilapia scale via thermal extraction method. The gelatins were then subjected to Ultraviolet-A (UVA) and Ultraviolet-C (UVC) irradiation for 0.5 to 2.5 h and the changes in gel strength, viscosity, and melting temperature were observed. Results obtained show a marked increase in the gel strength and viscosity of the gelatins. However, the effects on the melting temperature are minimal. Treatment with UVA and UVC improved the gel strength of the gelatins up to 5.12 ± 0.22 N and 4.75 ± 0.09 N, respectively. Further analysis using Fourier Transform Infrared (FTIR) Spectroscopy showed crosslinking formation in the polypeptide chains induced by UV irradiation. UVA was found to be more effective in enhancing the properties of scale gelatins compared to UVC. In general, UV-irradiated scale gelatins showed excellent properties compared to the commercial bovine gelatin. Results indicated the prospects of employing UV treatment in enhancing the properties of fish gelatin

Study on the Effect of Rice Husk Ash, Fly Ash and Palm Frond Ash in Geopolymer Cement

The research or the study of the effect of rice husk ash, fly ash and palm frond ash on geopolymer cement has been carried out and completed. The objective of the research is to determine the suitability of the produced geopolymer cement to be used in oil well cementing applications. Meanwhile, the effect of the curing period of cement and also the composition it is made of on the compressive strength of the geopolymer cement were also studied. The compressive strength testing was carried out on produced geopolymer cements since compressive strength is one of the main factors that determine the appropriateness of a cement to be used in cementing applications. The evolution of geopolymer cements is due to the environmental pollution caused by carbon dioxide release by industries particularly cementing and aggregate industries which could lead to global warming. Geopolymer cements also are good substitute for Ordinary Portland Cement (OPC) since OPC is known for its corrosion potential with carbon dioxide. Thus, the production and usage of geopolymer cement could curb all these problems. The scope of the research is limited to the three aforementioned raw materials to be used in compressive testing study in determining its suitability to be used in real life applications. Thus, the whole research is laboratory based. The methodology of the research can be divided into five major sections, which are, gathering relevant data and information, calculation of cement slurry proportions, geopolymer cement production, compressive strength testing of geopolymer cement and finally analysis of the results. The last two sections are very vital in justifying the results obtained from the research. Based on the results of the research, the curing period and composition of the cement significantly influence the compressive strength of the geopolymer cement. With the inclusion of aggregates and plasticizers, which were not used in this research, the geopolymer cement composed of rice husk ash, fly ash and palm frond ash has a high potential to be used in oil well cementing and might be an alternative for class G cement used currently, where further study is necessary in justifying it

Poor Perception of Body Weight Category amongst the Overweight and Obese with Chronic Hepatitis C: A Target for Intervention

Obesity in chronic hepatitis C (CHC) is associated with adverse hepatic and metabolic outcomes. This prospective study evaluates the agreement between self-perceived body weight (BW) status and measured body mass index (BMI) category and factors associated with its underestimation in CHC. Body size perception was measured with the Contour Drawing Rating Scale. Two hundred and seventy-three patients with CHC (overweight 45%, obese 18%) participated in this study. Although both overweight and obese demonstrated good body size perception, agreement between perceived BW and measured BMI categories was poor (κ = 0.315, 95% CI 0.231–0.399); 33% of overweight/obese respondents considered themselves normal or underweight. Male gender (OR 2.84) and overweight (OR 2.42) or obese BMI (OR 14.19) were associated with underestimation of BW category. Targeted interventions are needed to improve body weight perception, thereby enhancing the uptake of health advice on management of excess body weight in CHC

Characteristics of Problems in Problem-based Learning

This thesis focuses on characteristics of problems in Problem-based Learning (PBL). Problems initiate the students’ learning process in PBL. Several studies have shown that the quality of problems has a positive influence on students’ academic achievement and interest. In addition, the quality of problems has been shown to have a higher influence than the tutor’s performance and students’ prior knowledge on students’ learning. The implication of these findings is that designing good problems will result in better learning. However, there are very few studies which shed light on the characteristics of problems. To contribute to our understanding of problems characteristics and their influence on students’ learning, this thesis presents five studies. The five studies (1) explored the characteristics of problems in students’ and tutors’ perspectives, (2) developed, validated and tested the reliability of a problem quality rating scale to measure the characteristics of problems, and (3) used the rating scale to study the influence of problem familiarity on students’ learning