published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

This licentiate thesis presents our investigation of Saturn's inner plasma disk. The thesis gives an overview of the Cassini-Huygens project, what a plasma is and how we use the Langmuir probe to investigate it, various difficulties related to the measurements, the structure of the magnetosphere of Saturn, with special focus on the inner magnetosphere and the region around the Saturnian moon Enceladus. For our investigation we use the Cassini Langmuir probe to derive ion density and ion velocity in the region from 2.5 to 12 Saturn radii. We show that the dominant part of the plasma torus, ion density above ~15 particle/cm3, is located in between 2.5 and 8 Saturn radii (1 RS = 60,268 km) from the planet, with a north-southward extension of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cpm" />2 RS. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane, as expected since the Enceladus plumes are located in the south polar region. Also the azimuthal ion velocity vi,Θ is estimated, showing a clear general trend in the region between 3 and 7 RS, described by vi,Θ =1.5R2-8.7R+39. The average vi,Θ starts to deviate from corotation speed at around 3 RS and reaches down to ~68 % of corotation close to 5 RS. The Langmuir probe data show a clear day/night side asymmetry in both ion density and ion velocity, most prominent in the radial region 4-6 RS from the center of Saturn. The ion densities ni varies from an average of ~35 cm-3 for the lowest dayside values close to noon up to ~70 cm-3 for the highest nightside values around midnight. The azimuthal ion velocities vi,Θ varies from ~28-32 km/s at the lowest dayside values around noon to ~36-40 km/s at the highest nightside values around midnight. This gives an azimuthal ion velocity difference between noon and midnight of Δvi,Θ ~5-10 km/s. The day/night asymmetry is suggested to be due to dust-plasma interaction.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Highly reliable data storage for satellites and spacecraft is a challenging technology. The space environment is a unique combination of many environmental factors which impact the reliability and even the very survival of electronic systems. The need for space qualified memory is becoming even more important with the advent of on-board data processing which requires rapid access to large data bases. This paper describes the unique environmental and design considerations that must be taken into account for a magnetic disk that is designed to operate for years in the space environment.

During the process of the Singapore economy development, its ¡§elite government¡¨ has to attract the multinational companies to invest in Singapore. Among the public organization, Singapore Economic Development Board¡]EDB¡^ is the statutory institute of marketing the Singapore investment environment. After set up in 1961, EDB has been engaged in creating employment opportunities. In order to improve the most valuable asset of Singaporean, EDB also designs several human resource training programs and training centers. The organization culture of EDB is the key success factor which contributes to following the changes of international economy situation and working out suitable economic policies for Singapore industry. In the past the government takes the responsibility of leading the Singaporean toward the economic vision, but recently the Singapore government aggressively encourages the people to start up a new enterprise instead to avoid depending foreign investments excessively and to balance the economic ecosystem to achieve more value-added. My thesis does a case study of hard disk drive industry in ch4 to show the notable position of EDB in industry development context. In the ch5 the emerging biomedical industry will discuss the transformation from national economic plans to technology entrepreneurship. The future of Singapore economy development depends on whether the policy works or not.

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Back pain is a prevalent musculoskeletal disorder affecting populations worldwide. Degeneration of the intervertebral discs (IVD) is indicated to be one of the main etiologic factors of back pain. The loss of proteoglycan and consequently dehydration and reduction of swelling of the intervertebral disc core, the nucleus pulposus (NP), is one of the earliest degenerative events. The replacement of large vacuolated notochordal cells by the smaller chondrocyte-like cells in the NP coincide with the onset of IVD degeneration, the loss of the notochordal cells was therefore postulated to be a cause of the degeneration and associated with ageing . To date, the true origin of the smaller chondrocyte-like cells was still under dispute. In this study, Egfp reporter was constitutively and permanently activated in the notochord via specific Cre expression by the Foxa2mNE enhancer under the recombination system in the Foxa2mNE-cre; Z/EG double transgenic mice. The notochord descendent cells were therefore labeled with green fluorescent protein (GFP) and their localization and expression characteristic were tracked during development, maturation, ageing of mouse tail IVD. To further investigate the cellular changes during degeneration, disc degeneration in the murine disc was induced by puncture. The GFP labeled notochord cells were demonstrated to be entrapped and remained in the NP of the murine disc. With the validation of degeneration by the multichromatic FAST staining, a grading system based on altered sulfated glycosaminoglycan content and cellular organization specialized to murine disc was proposed. The segregation of the notochordal NP cell mass segregation was found to be a common pathway of both age-related and puncture-induced degeneration. While apoptosis and loss of NP cells was presented in puncture-induced disc degeneration, invasion of lamellae cells was only found in severely degenerated discs. Consistent with the findings of the murine puncture model, increased expression of Col2a1 and Col1a1 were demonstrated in punctured discs by ISH, which the notochordal NP cells were showing a remarkable elevation in expression. The data supports a chondrogenic differentiation of the endogenous notochordal cells instead of invasion of chondrocyte-like cells into the NP. Three NP markers identified as a common genes from microarray of rat and human NP, (Carbonic anhydrase3 (Car3), UDP-N-acetyl-alpha-D-galactosamine:polypeptide; N-acetylgalactosaminyltransferase 3 (Galnt3) and HOP homeobox (Obl)), were found specifically co-localized with the notochord descendent cells in all ages and different time-points after puncture, suggesting them as novel but reliable markers for notochordal NP cells. This study provides direct evidence of the origin of NP cells in aged and degenerated IVDs using transgenic mice, and thus enhances the understanding of the role of notochordal cells in the progression of IVD degeneration. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Intervertebral disc (IVD) degeneration could lead to many serious complications including low back pain and disc herniation. However, the mechanism of disc degeneration is not fully understood, hindering the development of the therapeutics to cure this disease. The integrity of the nucleus pulposus (NP), which is derived from the notochord and situated in the core of the IVD, has long been implicated in the function and homeostasis of the IVD. Previous puncture-induced disc degeneration mouse model showed segregation of NP cell mass during the early stage of disc degeneration, indicating that an alteration in the cell adhesion molecule activities is involved in this process. By microarray analysis, our group have revealed specific expression of Cdh2 gene, encoding cadherin 2/N-cadherin, a subtype of cadherins in the NP cells, suggesting a regulatory role of cadherin 2 in the IVD. Cadherins are single transmembrane glycoproteins mediating calcium-dependent intercellular adhesions. Cadherin 2 is involved in chondrogenesis and skeletogenesis, suggesting that it is important in skeletal development and function. This study hypothesized that cadherin 2 is required in the normal IVD development and homeostasis. The purposes of this project is firstly to fully characterize changes in cadherin 2 expression in the normal and degenerative discs in rodent and human, and secondly to examine the effect of loss of function of cadherin 2 on IVD homeostasis by functional blocking of the protein in the rodent NP and conditional knock out of cadherin 2 from the murine NP. The rodent adult NP is similar to human fetal NP, where cadherin 2 is homogeneously expressed in the cell membranes of the notochordal (NC) cells, suggesting that cadherin 2 is a potential NC cell marker. The rodent degenerative NP is similar to human adult NP, where down-regulation of cadherin 2 is observed, the NC cells are replaced by small round cells, and the cell-cell contact is lost. Blocking cadherin 2 function in the rodent NP and conditional knock out of cadherin 2 in the notochord and consequently the NP will lead to transformation of NC cells into small cells, loss of cell-cell contact and a change in the extracellular matrix (ECM), suggesting that cadherin 2 is important in the maintenance of the phenotype and intercellular adhesion of the NC cells. In conclusion, this study indicates that cadherin 2 is mainly expressed in the NC cells of the NP and serves as a potential NC cell marker. It plays a regulatory role in the IVD homeostasis through the maintenance of the NC cell phenotype by intercellular adhesions. This study contributes to the knowledge about the role of cadherin 2 in the disc homeostasis and the early mechanism of disc degeneration, and this would help in developing a therapeutic method to intervene or even reverse the disease process of disc degeneration. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy