The study describes the labour conditions for migrants in Sweden and aims at examining who is to benefit from increased labour migration. The qualitative method with a literature review is complemented with an interview in order to incorporate undocumented migrants’ perspective. Labour migration is discussed with the possible progress towards circular migration and thereafter incorporated in analyse with the dual labour market theory. The results show that it is foremost Swedes and migrants from inside the EU/EEA region that benefit from labour migration while migrants from outside the region will have to follow employers’ needs. This has lead to labour permits in low wage sectors were migrants supplement to structural inflation. The demand for cheap labour has also led to the exploitation of undocumented migrants who are paid starvation salaries. If these services are increasingly requested, serious employers might find it difficult to stand against decreasing minimum salaries and the welfare will decrease for more groups of employers. Meanwhile, changing demography is predicted to necessitate increased migration to sustain an economical growth in Sweden. This would also suggest that Sweden receives the main benefit from increased labour migration.

This study discusses the three-dimensional refraction of progressive wave trains propagating over a bottom of circular concentric contours and the results are expressed in a polar coordinate. First, a general differential formulation of refraction is derived via three different methods: by transferring from its original Cartesian form to the polar coordinate, by applying the Fermat¡¦s principle in polar coordinate, and by applying the conservation of waves in polar coordinate. All three approaches give the same governing equation; hence, its correctness is verified. Based on this governing equation, the wave ray, the phase function, the constant phase line, and the refraction coefficient are all determined. In the present refraction problem for an originally uniform wave train propagating over a bottom of circular concentric contours, a few special features, including the cusps of constant phase lines due to the effect of bottom, and the envelope composed of these cusps, are present. All these refraction properties can be expressed in terms of both a snapshot and a time evolution of constant phase lines. In the lee side of the shoal, there exists a sheltered zone that is enclosed by the envelope of the cusps. In this zone, wave rays intersect and the corresponding caustic problem arises, and all possible combinations of intersecting rays are also specifically described in this study. The difficulty of classical ray theory for the caustic problem is overcome and the caustic phenomenon and its refraction coefficients are determined explicitly in this study.

Nowadays, the bevel gears are widely applied in the industry for the intersected-axial transmission system. But the applications of the bevel gears are mostly limited to the usage of involute bevel gears. In this thesis, the bevel gear with circular-arc tooth profiles is derived by using general theorem of conjugate surfaces, coordinate transformation, constrained meshing equation, and spherical trigonometry. According to the bevel gears with circular-arc tooth profile derived above, the analyses and discussions of the interference are proposed. The interference situation is detected by applying the phase lead-lag concept while circular-arc curve is moving on the spherical cross-section. Furthermore, the ideal conditions to avoid occurrence of interference are proposed. Design charts for the maximum values of tooth profile angle are also constructed as a reference for designers. The 3D solid models of the bevel gear with circular-arc tooth profiles are constructed by using the computer software (Pro/E). Finally, the transmission ability is verified through the computer animation using CAE software (Visual Nastran). It is believed that the mathematical models and design method developed in the thesis will provide a useful foundation for the further studies.

In recent years there has been a growing demand for reduced mass, small launch volume, and, at the same time, high-gain large-aperture antenna systems in modern space-borne applications. This dissertation introduces new techniques for dual-band reflectarray antennas to meet these requirements. A series of developments is presented to show the dual-band capability of the reflectarray. A novel microstrip ring structure has been developed to achieve circular polarization (CP). A C/Ka dual-band front-fed reflectarray antenna has been designed to demonstrate the dual-band circular polarized operation. The proposed ring structure provides many advantages of compact size, more freedom in the selection of element spacing, less blockage between circuit layers, and broader CP bandwidth as compared to the patches. An X/Ka dual-band offset-fed reflectarray is made of thin membranes, with their thickness equal to 0.0508 mm in both layers. Several degrading effects of thin substrates are discussed. To overcome these problems, a new configuration is developed by inserting empty spaces of the proper thickness below both the X and Ka band membranes. More than 50 % efficiencies are achieved at both frequency ranges, and the proposed scheme is expected to be a good candidate to meet the demand for future inflatable antenna systems. An X/Ka dual-band microstrip reflectarray with circular polarization has also been constructed using thin membranes and a Cassegrain offset-fed configuration. It is believed that this is the first Cassegrain reflectarray ever developed. This antenna has a 0.75-meter-diameter aperture and uses a metallic sub-reflector and angular-rotated annular ring elements. It achieved a measured 3 dB gain bandwidth of 700 MHz at Xband and 1.5 GHz at Ka-band, as well as a CP bandwidth (3 dB axial ratio) of more than 700 MHz at X-band and more than 2 GHz at Ka-band. The measured peak efficiencies are 49.8 % at X-band and 48. 2 % at Ka-band. In summary, this dissertation presents a series of new research developments to support the dual-band operation of the reflectarray antenna. The results of this work are currently being implemented onto a 3-meter reflectarray with inflatable structures at the Jet Propulsion Laboratory and are planned for other applications such as an 8-meter inflatable reflectarray in the near future.

The study aims to explore flow-induced vibration of shear flow past a circular cylinder. The major parameters in the experiment are the natural frequency of the cylinder, and the velocity and velocity gradient of the shear flow approaching the cylinder. The vibration of the cylinder in a water tunnel were measured by two accelerometers to simultaneously obtain the vibration amplitudes in both the streamwise and cross-stream directions. The experimental results show that in the shear flow the cylinder tends of vibrate the orbits of the cylinder vibration become in the streamwise direction while in uniform flow the cylinder vibrates in all directions in the X-Y plane the tendency is obvious for the cylinder with high natural frequency (13Hz). The orbits of the cylinder with low natural frequency (9Hz) are basically similar in shear flow and in uniform flow.

The present study developes a mixed finite element formulation for the analysis of piezoelectric circular and annular plates. This formulation combines the conventional displacement-electric potential type variational principle and the piezoelectric Reissner`s principle with a weighting factor which represents ratio of weights imposed on the above two variational principles, and which can be adjusted by comparing with experiment results. With this formulation, stresses and electric displacements, like displacements and electric potential, are primary variables and are continuous across elements and element interfaces. Also, all displacement, stress, electric displacement, and electric potential boundary conditions can be easily and exactly imposed. Static deformations and vibration frequencies of some typical piezoelectric circular and annular plates are then obtained with the present approach and are compared with those by other methods. Based on experiment results in the literature, it is found that better results could be obtained in general by the present mixed finite element formulation than the others when 1 is chosen as the weighting factor.

Dragon grouper nervous necrosis virus (DGNNV), a betanodavirus, is the causative agent of viral nervous necrosis (VNN) in dragon grouper (Epinephelus lanceolatus). In our study, capsid protein of DGNNV was expressed in Escherichia coli. We mutated arginines at N-termini capsid protein to investigate the role of arginines at 29-31th position. When capsid protein lost 25 amino acids at N-termini VLPs form, mutation in any two arginines at 29-31 position to alanine could the prohibit VLPs formation. Another extending three arginines at 23-25 position wouldn¡¦t increase the RNA encapsulation into VLPs. Furthermore, N-termini mutated VLPs were all RNase resistance like wt-VLPs, but the yield was distinctly less than wt-VLPs. In the single point alanine mutations, the VLPs yield of R29A was apparently higher than others (R30A and R31A). Using circular dichroism to observe the thermal denature process and thermal stability of DGNNV VLPs, we found the Tm about 60¢J of VLPs wouldn¡¦t alter even if arginines at 23-31 position were mutated. The findings suggested the VLPs of mutated arginines at 23-31 position wouldn¡¦t affect RNase resistance and thermal stability, but the yield were lower. Another, the arginines at the 30 and 31 position is more important than at 29 position for formation of VLPs.

The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material. In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations. / published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / toc / Medicine / Doctoral / Doctor of Philosophy

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