On an Ecological Model of Mutualisim Between Two Species With a Mortal Predator

In this paper, we study an ecological model of a three-space food chain consists of two logically growing mutual species and third species acts as a predator to second mutual species with Holling type II functional response. This model is constituted by a system of nonlinear decoupled ordinary differential equations. By using perturbed method, we identify the nature of the system at each equilibrium point and also global stability is investigated for this model using Lypanov function at the possible equilibrium points

Age- and Sex-Associated Changes in mRNA Expression of Neurodegenerative Disorder-Related Molecules in the Hippocampus and Cerebellum of Rat Brain

Age-associated oxidative stress is involved in neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases, and sex-associated differences may also affect the risk for these neurodegenerative diseases. We compared the effects of aging and sex on the mRNA expression of five molecules that are closely related to oxidative stress, along with Alzheimer’s and Parkinson’s diseases in the hippocampus of both male and female Fischer 344xBrown Norway (F344BN) rats. The reverse transcription polymerase chain reaction was used to determine the mRNA expression level of superoxide dismutase 2 (SOD2), heme oxygenase 1 (HO1), amyloid precursor protein (APP), -site APP-cleaving enzyme 1 (BACE1), and -synuclein (ASN) in the hippocampus of 3 groups of male and female (young rats, aged rats, and very aged F344BN rats). No significant age- or sex-related changes were observed in the expression levels of SOD2, APP, or BACE1 mRNAs. The expression of HO1 mRNA in the very aged female rat hippocampus was significantly higher than that observed in the young female control and the aged females, when compared to male counterparts. No significant age-associated changes were observed in the expression of ASN mRNA; however, the expression of ASN was significantly higher in the hippocampus of male compared to female rats. Because the accumulation of iron in the brain plays a key role in Alzheimer’s and Parkinson’s diseases, we also investigated age- and sex-related expression of five mRNAs that are closely related to iron storage, transportation, and metabolism: ferritin heavy chain (FTH), ferritin light chain (FTL), transferrin receptor (TfR), divalent metal transporter 1 (DMT1), and iron-regulatory protein 1 (IRP1). No significant age-related changes were observed in the expression levels of any of these five molecules. The overall expression of FTH and IRP1 mRNAs was significantly lower in the hippocampus of male rats when compared to females. This study paves the way for the further investigation of age- and sex-related changes in the protein expression and activities of these molecules, and will help clarify the mechanisms by which oxidative damage may affect neurodegenerative diseases

Optoelectronic devices and packaging for information photonics

This thesis studies optoelectronic devices and the integration of these components onto optoelectronic multi chip modules (OE-MCMs) using a combination of packaging techniques. For this project, (1×12) array photodetectors were developed using PIN diodes with a GaAs/AlGaAs strained layer structure. The devices had a pitch of 250μm, operated at a wavelength of 850nm. Optical characterisation experiments of two types of detector arrays (shoe and ring) were successfully performed. Overall, the shoe devices achieved more consistent results in comparison with ring diodes, i.e. lower dark current and series resistance values. A decision was made to choose the shoe design for implementation into the high speed systems demonstrator. The (1x12) VCSEL array devices were the optical sources used in my research. This was an identical array at 250μm pitch configuration used in order to match the photodetector array. These devices had a wavelength of 850nm. Optoelectronic testing of the VCSEL was successfully conducted, which provided good beam profile analysis and I-V-P measurements of the VCSEL array. This was then implemented into a simple demonstrator system, where eye diagrams examined the systems performance and characteristics of the full system and showed positive results. An explanation was given of the following optoelectronic bonding techniques: Wire bonding and flip chip bonding with its associated technologies, i.e. Solder, gold stud bump and ACF. Also, technologies, such as ultrasonic flip chip bonding and gold micro-post technology were looked into and discussed. Experimental work implementing these methods on packaging the optoelectronic devices was successfully conducted and described in detail. Packaging of the optoelectronic devices onto the OEMCM was successfully performed. Electrical tests were successfully carried out on the flip chip bonded VCSEL and Photodetector arrays. These results verified that the devices attached on the MCM achieved good electrical performance and reliable bonding. Finally, preliminary testing was conducted on the fully assembled OE-MCMs. The aim was to initially power up the mixed signal chip (VCSEL driver), and then observe the VCSEL output

Colloidal Microgel Particles: Confinement Of Liquid Crystals And Characterization

Liquid crystals that are confined within curved boundaries are of interest to many scientists due to their important role in optoelectronic technologies. As such, intensive research has been conducted with various types of liquid crystals constrained to droplets or cylindrical environments. Such studies are significant because the curvature of liquid crystals costs elastic energy, and hence, we observe rich physical phenomena such as change in the director field that otherwise would have been hidden. Most of the fundamental studies of liquid crystalline phases of cellulose nanocrystals were conducted in the cells with flat boundaries, limited to certain concentrations. Here, we report cellulose nanocrystals confined to pnipam microspheres using inverse emulsion polymerization technique with microfluidics device. The chiral nematic phase of cellulose nanocrystals are preserved within the polymer matrix, as characterized by optical microscopy. The droplet radius, R of the microgels can be adjusted by changing the volumetric flow rate of oil phase in a microfluidics device. Notably, the fabricated CNCs-PNIPAM microgels are able to exhibit swelling-deswelling behavior upon temperature change with well-organized structure. I will also discuss how one applies a real-space imaging technique, known as Differential Dynamic Microscopy (DDM), to characterize such microgel particles

Biogenesis, Assembly and Intracellular Trafficking of Junin Arenavirus Envelope Glycoprotein Complex

An unusual feature in the arenavirus envelope glycoprotein complex (GP-C) is the presence of a myristoylated stable signal peptide (SSP) in addition to the receptor binding subunit G1 and the transmembrane fusion subunit G2. Genetic studies were employed to understand the structure-function of the GP-C complex, with emphasis on elucidating the role of SSP in arenavirus life cycle. We present genetic evidence that support the inclusion of G2 as a member of Class I viral fusion protein, where membrane fusion is mediated by six-helix bundle structure as in HIV and Influenza viruses. Furthermore, we have identified crucial roles for SSP in the GP-C complex. In the mature glycoprotein complex, SSP assumes a bitopic membrane topology with both its N and C termini in the cytosol, and a short ectodomain loop. This membrane orientation allows it to mask the endogenous endoplasmic reticulum retrieval signals in the cytoplasmic tail of G2 thereby allowing the transit of fully assembled GP-C complex through the Golgi to the cell surface. SSP also interacts with the ectodomain of G2 on the outer surface of the membrane. This interaction is critical in modulating the pH at which the membrane fusion is activated. The SSP-G2 pocket has been identified as the target of newly discovered small-molecule inhibitors of arenaviral entry. Beyond its role in intracellular trafficking and pH-dependent membrane fusion of GP-C complex, SSP might be involved in virus assembly and budding. Studies employing immunogold electron microscopy indicated that GP-C complex clusters into microdomains of 120 nm size independent of other viral proteins. Clustering of GP-C into membrane microdomains is neither influenced by SSP myristoylation nor by the co-expression of the matrix protein do Z. Regions of plasma membrane containing Z not co-localize with GP-C containing microdomains. Clustering of proteins or lipids on the plasma membrane may bring Z and GP-C together at the virus budding sites. Taken together, these data have contributed to the understanding of the unique subunit organization in GP-C complex and the mechanisms underlying efficient co-ordination of these subunits to execute significant functions in the arenavirus life cycle

STUDIES ON THE PERCENTAGE VARIATION OF RESISTANCE OF PVC-GRAPHITE THICK FILM RESISTORS

The percentage variation of resistance of PVC-graphite thick film resistors has been studied. Two different grain sizes of graphite, as well as four different compositions of PVC- graphite are adopted in the preparation of thick film resistors. Among the four different compositions of PVC-graphite i.e. 90%:10% to 60%:40%, 90%:10% PVC-graphite composite thick film resistor shows the least variation with temperature changes. This can be attributed to high composition of graphite. The variation will be lowered down with a decrease in the loading fraction of PVC in thick film resistors. The percentage variations of resistance of PVC-graphite thick film resistors, after 700C for 1000 hours, or after 30 cycles thermal shock tests as well as the variations after the short term overload tests, have been measured and studied. A possible explanation on these experiments is also presented