Dissertations / Theses on the topic 'Second generation'

Thesis (MEng)--Stellenbosch University, 2000.
ENGLISH ABSTRACT: The SUNSAT RAMDISK was studied, and tests performed to assess its flight readiness. Errors were detected, and modifications had to be made to ensure proper operation. SUNSAT was subsequently launched, and to date the RAMDISK is still functioning correctly. The flight readiness testing of the RAMDISK was considered a pre-study to designing a second generation RAMDISK. A conceptual mass memory storage device support structure was designed. This second generation RAMDISK, or memory drive is intended to be used on a second generation SUNSAT, or SUNSAT 2. The design is targeted for implementation in fields programmable gate arrays (FPGA's) and was realised using VHDL. This hardware description language is an accepted standard, and can be implemented in a number of different programmable logic devices; both SRAM and fuse-link based. Simulations were performed to verity the functionality of the design, and to determine whether the data transfer specifications could be met using programmable logic devices. A modular design methodology was followed. The memory drive was designed so that any type and amount of memory can be added to the drive without a major design change. The simulations indicated that a data capturing speed of 130 Mbits/s could be maintained.
AFRIKAANSE OPSOMMING: Die SUNSAT massa geheue module is bestudeer, en toetse is daarop uigevoer om die vlug gereedheid te bepaal. Foute is gevind, en veranderinge moes aangebring word om korrekte werking te verseker. SUNSAT is gelanseer en die geheue module werk tot op datum nog korrek. Die geheue module se vlug gereedheid toetse is beskou as In voor studie vir die ontwerp van In tweede generasie geheue module. In Konseptueie massa stoor toestel struktuur is ontwerp. Hierdie tweede generasie geheue module, of geheue skyf is bedoel om op In tweede generasie SUNSAT, of SUNSAT 2 gebruik te word. FPGA's is die teiken tegnologie vir hierdie ontwerp en VHDL is gebruik om die ontwerp te realiseer. Hierdie hardeware beskrywingstaal word as In standaard aanvaar en kan in verskillende herprogrammeerbare tegnologieë gebruik word. Sirnulasies is gedoen om die funksionaliteit van die ontwerp te verifieer, en om te bepaal of die nodige data oordragstempo gehandhaaf kan word met herprogrammeerbare tegnologie. In Modulêre ontwerpsfilosofie is gevolg. Die geheue skyf is ontwerp sodat dit enige tipe en hoeveelheid geheue kan ondersteun sonder om groot veranderinge aan die ontwerp te doen. Die sirnulasies toon dat In data oordragstempo van 130 Mbits/s gehandhaafkan word.

Photonic crystals emerged at the end of the last decade as a new frame to control the interaction between radiation and matter. The potential advances that such structures could report in photonics technology has lead to an increasing research focused on the implementation of photonic crystals possessing full photonic band gaps, hindering the fact that more simple structures, possessing band gaps in selected directions of space, may also provide strong control of the electromagnetic radiation leading to the observation of many new interesting phenomena. In fact, the scope of this control is not limited to a linear interaction and can be extended to nonlinear interactions of any order.

In this work we present a study of the second order nonlinear interaction from nonlinear organic molecules placed within two different types of photonic crystals. First, we will discuss the enhancement and inhibition of the radiation at the second-harmonic frequency of a sheet of dipoles embedded in a 1D photonic crystal. The experimentally observed reflected second-harmonic intensity as a function of the angle of incidence shows sharp resonances corresponding to the excitation of the SH field in a local mode within the forbidden band in the structure, which position depends on the size of the defect, and additional resonance at the high angular band edge, which position is independent of the size of the defect. Comparison among these results and the SH intensity reflected by the same monolayer in free space (which presents a bell shaped radiation pattern as a function of the angle of incidence), shows an enhancement of the radiation at the resonances, and strong inhibition of the radiation at other angles within the gap. Theoretical simulation of the experiment shows a good agreement with the experimental results.

A detailed analysis of the enhancement and inhibition phenomena occurring in these structures shows a clear dependence of the resulting intensity with the position of the monolayer within the defect and with the dipole orientation. The change in phase difference between the oscillating dipoles and the field at the SH frequency at the monolayer as it is moved within the defect is found to play a determining role in the final energy transfer to the second-harmonic field. The resulting enhancement and inhibition of the radiation may be studied in terms of a nonsymmetric contribution of the different components of the field to the energy transfer process.

The second configuration studied in the present work consider the experimental demonstration of second-harmonic generation in a 3-dimensional macroscopically centrosymmetric lattice formed by spherical particles of optical dimensions. In such photonic crystals, the local breaking of the inversion symmetry at the surface of each sphere, allows for the existence of a nonvanishing second order interaction. The growth of the SH radiation is provided by the phase-matching mechanism caused by the bending of the photon dispersion curve near the Bragg reflection bands of this photonic crystal. Experimental evidence of this phase-matching mechanism, inherent of such crystals, is reported in this work. By measuring the SH intensity radiated from several crystals with different concentrations, we obtained the angular dependence of this type of emission and confirmed the surface character of the nonlinear interaction. A simplified theoretical model shows very good agreement with the experimental results. It is important to notice that in this mechanism of SHG, the nonlinearity of the molecule is independent of the phase-matching mechanism, that is inherent to the periodicity of the crystal.

In conclusion, the results obtained show a clear influence of the photonic crystals in the radiated SH intensity, resulting in enhancement and inhibition of the dipoles radiation.

Operators on a manifold with (geometric) singularities are degenerate in a natural way. They have a principal symbolic structure with contributions from the different strata of the configuration. We study the calculus of such operators on the level of edge symbols of second generation, based on specific quantizations of the corner-degenerate interior symbols, and show that this structure is preserved under compositions.

The current DICOM communication standard for radiotherapy is outdated and has serious design issues. A new version of the standard, known as DICOM 2nd generation for Radiotherapy, has been introduced and this thesis examines new concepts relating to radiation delivery. Firstly, some background into the practice of radiotherapy is given, as well as a description of the DICOM standard. Secondly, the thesis describes the design issues of the current standard and how the 2nd generation aims to solve these. Thirdly, the thesis explores the conversion of a first generation C-Arm Photon/Electron treatment plan to the second generation RT Radiation and RT Radiation Set IODs. A converter is implemented based on a model proposed in a previous work. With some simplifications, the conversion of Basic Static and Arc treatment plans is shown to be successful. Conversion of further dynamic plan types is judged to be fairly simple to implement following the same methodology. The conversion model’s efficacy and testability are discussed and while the model is flexible and facilitates extension to further modalities some areas of improvement are suggested. Lastly, a GUI for the converter is demonstrated and the possibilities of user interaction during conversion are discussed.

Family businesses are prevalent in South Africa and throughout the world. Succession is one of the largest challenges facing family businesses. It has been estimated that only one third of family businesses survive to the second generation. This study attempts to determine what the main features are to promote successful family business succession and continuity. The family chosen for this research is the Venter family. The research has scaled the various influencing variables from the literature review into the following focus areas: relationships, conflict, vision, effective succession characteristics and continuity. The findings reflect many instances found in the literature, some are: individuals can manage themselves and have relationships with others; have the ability to resolve conflicts; have mutual support and trust; there is respect between the founder and successor; the business vision is clear; communication is open and clear and decisions are based on expertise and knowledge. Many other aspects are highlighted in the research that follows. In addition, the study attempts to identify the generational effects, the major characteristics of the family owned succession process and the views of the predecessors on the succession process and the post succession period.

Collagen is the most abundant structural protein in the human body. When it is excited by femtosecond near infrared laser, second harmonic generation (SHG) signal at half the wavelength of the excitation wave is excited. For imaging thick tissues, the SHG signal is collected in the backward direction. The objective of this work is to elaborate the origin of the backward SHG in collagen at the fibril level and investigate some of its optic characteristics. The optic characteristics investigated include the wavelength dependence of SHG intensity, which is useful to analyze SHG in collagen tissues. However, the current published results are inconsistent. We study the microscopy system factors affecting the wavelength dependence and calibrate them by measuring the wavelength dependence of SHG intensity in a BaB₂O₄ crystal. With the proper calibration, typical wavelength dependence SHG spectra from mouse tail and Achilles tendon are investigated. The backward-collected SHG signal includes the backward generated SHG, and the forward generated but backward scattered SHG. Those two sources of the total backward SHG have different properties due to the difference in phase mismatch in the forward and backward directions. Here a non-invasive method is developed to separate them by using pinholes. By varying the pinhole size in a confocal multiphoton microscopy, the proportion of the backward scattered SHG to the total backward SHG can be obtained. Our results indicate that backward scattered SHG may not be the major source of backward SHG in the mouse tail tendon, which means significant SHG is purely generated in the backward direction. A large phase mismatch exists in generating backward SHG. Nevertheless, significant backward generated SHG has been observed in collagen tissues. We hypothesize that the periodic lattice structure of fibrillar collagen can provide a virtual momentum to assist the backward phase matching. Here the backward SHG phase matching is investigated in theory, simulation, and experiments, which are consistent and support the hypothesis. The various properties investigated in this thesis can provide a better understanding about SHG in collagen tissues and lead to new applications of SHG microscopy in diagnosing collagen related diseases in the future.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

Second-generation immigrants represent a significant subgroup of the Canadian population and workforce; however, the career development of adult second-generation immigrant women has not been examined. In order to understand the career development of second-generation women, an integration of Gottfredson and the feminist-multicultural career development theories was used. According to this integrated framework, it was important to understand: 1) sex-roles and gender and occupational stereotypes; 2) the effect of culture (i.e., familial, social class, and societal); 3) the effect of socio-cultural factors and systemic institutions (e.g., occupational stereotypes and discrimination); and 4) the effect that immigrant mothers had on the career development of second-generation immigrant women. A phenomenological approach was used to examine the career development experiences of second-generation immigrant women. Participants were 21 second-generation immigrant women between the ages of 24 and 39 years old, who had been working for at least 2 years. The women participated in an individual interview and co-created two pictorial representations of their own and their family's career development experiences. Participants were asked to describe their career aspirations, interests, values, and decision-making process as well as the influence of gender, family, culture and other societal factors on their career development. Results showed that the career development of second-generation immigrant women was very similar to that of North American women, indicating that the struggles that North American women faced seemed to be a cross-cultural phenomenon that transcended cultural and immigration status boundaries. Additionally, findings suggested that participants were influenced by their family and culture to pursue post-secondary education and culturally acceptable careers. It was also found that school programs (e.g., co-operative education program) were influential becaus
Les immigrants de deuxième génération constituent un sous-groupe important de la population Canadienne et des travailleurs canadiens; toutefois, le développement de carrière des immigrantes de deuxième génération d'âge adulte n'a jamais été examiné. Afin de comprendre le développement de carrière des immigrantes de deuxième génération, une synthèse de la théorie de Gottfredson et du développement de carrière féministe multiculturelle ont été utilisés. Selon ce cadre de travail, il était important de comprendre ce qui suit : 1) les rôles sexuels et les stéréotypes; 2) les influences culturelles (p. ex. famille, classe sociale et société); 3) les incidences des facteurs socioculturels et des institutions systémiques (p. ex. stéréotypes et discrimination professionnels); et 4) l'influence des mères immigrantes sur le développement de carrière des immigrantes de deuxièmes génération. Une approche phénoménologique a été utilisée pour étudier le développement de carrière des immigrantes de deuxième génération. Le groupe de participantes était constitué de 21 immigrantes de deuxièmes génération âgées entre 24 et 39 ans, et qui travaillaient depuis au moins deux ans. Les femmes ont passé une entrevue individuelle et elles ont créé en collaboration deux représentations graphiques, l'une de leur propre développement de carrière et l'autre du développement de carrière de leur famille. Les participantes ont décrit leurs aspirations professionnelles, leurs intérêts, leurs valeurs et leur processus décisionnel ainsi que l'influence du sexe, de la famille, de la culture et d'autres facteurs sociaux sur leur développement de carrière. Les résultats ont démontré que le développement de carrière des immigrantes de deuxième génération était très semblable à celui des femmes nord américaines, ce qui indique que les obstacles auxquels ces dernières font face semblent constituer un phénomène interc

Second Harmonic Generation has traditionally been restricted to crystals; however, due to the development of highly sophisticated fabrication technology, poling and phase matching techniques, it has now become feasible in glass fibres and waveguides which are widely used in nonlinear optics. For instance, silica glass based Photonic Crystal Fibres (PCF) exhibit long coherence lengths and controllable optical properties such as chromatic dispersion despite low second order nonlinearity. Given such benefits, the numerical modelling and analysis of optical waveguides accurately and efficiently has become vital for the advancement of nonlinear optics. Hence, this thesis focuses on enhancing the Second Harmonic Generation in optical waveguides through the use of different structures and different materials, and demonstrating the same by numerical simulations. In this thesis, the accurate and numerically efficient Finite Element based Beam Propagation Method has been employed to investigate the evolution of Second Harmonic Generation in highly nonlinear SF57 soft glass Equiangular Spiral PCFs. Further, the H-field based Finite Element Method has been employed for the stationary analysis of Photonic Crystal Fibres. It is shown here that the second harmonic output power in highly nonlinear

The purpose of this study was to observe the correlation between ethnic identity and gender as well as the relationship between ethnic identity and one’s country of origin. The study participants (n=335) were recruited through the social media sites Facebook, Twitter, Linked In, and Reddit. Participants completed the 15-question Multigroup Ethnic Inventory Measure (MEIM) and a Demographic Questionnaire, all done completely online. It was hypothesized that participants’ level of ethnic identity as measured by MEIM scores would differ significantly between the genders. Furthermore, it was posited that participant’s level of ethnic identity would differ significantly between countries of origin. Both hypotheses were supported. Implications of the study findings and recommendations for future research are discussed.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
Second generation biodiesel fuels extracted from sources such as beef tallow and castor bean oil have gone through an increase in production, as they are being gradually added to soybean biodiesel which constitutes the primary biofuel in the country. These alternative materials have potential do increase the fuelâs oxidation stability and, specifically in the case of beef tallow, reduce the cost of producing biodiesel. However, these sources also contribute to making the properties of the biodiesel/diesel blend more distant from those of conventional diesel fuel. Beef tallow biodiesel, for example, has a cetane number of 64.70, compared to 46.44 the soybean and 48 for mineral diesel fuel. In the case of castor bean biodiesel, its viscosity is 14.5 cSt, while soybeanâs is 4.2 cSt and mineral dieselâs is 2.5. It is expected that these unique characteristics should have noteworthy consequences in the injection, tomization and combustion processes of the fuel. This work intends to determine the extent of these consequences by characterizing each second generation biodiesel fuelâs impact on the apparent heat release rate. To this end, experimental data on cylinder pressure and a heat release â or energy - analysis model on a combustion zone were utilized. The data were obtained from a medium sized turbo diesel engine operating at steady state for three different load levels. Biodiesel and diesel blends were prepared at concentration levels B10, representative of current commercial use, and B20, corresponding to a greater biofuel adoption in a future scenario. Second generation sources were also compared to data from soybean biodiesel, which forms around 75% of Brazilâs biodiesel production. At B20 concentrations, it was found that beef tallow biodiesel, due to its higher cetane number, hastened combustion by about 1◦ compared to soybean and 3◦ compared to mineral diesel. This anticipation in ignition also caused a reduction in the amount of fuel consumed as a premixed flame. Combustion of castor bean biodiesel was mostly unchanged for high and medium loads compared to mineral diesel fuel. However, on the low load configuration (BMEP = 250kPa) and at B20 concentration, it caused a significant delay in combustion, likely from the collision of the fuel jet against the cylinder wall.
Os biodieseis de segunda geraÃÃo oriundos de fontes, tais como o sebo bovino e a mamona, vÃm experimentando uma expansÃo em sua produÃÃo, sendo adicionados gradualmente ao biodiesel de soja, que constitui a matÃria-prima predominante no paÃs. Essas matÃrias-primas alternativas podem aumentar a estabilidade à oxidaÃÃo do combustÃvel e, no caso do sebo, diminuir o custo de produÃÃo do biodiesel. Contudo, elas tambÃm contribuem para um maior distanciamento entre as propriedades das misturas diesel/biodiesel e o Ãleo diesel convencional. O biodiesel proveniente do sebo bovino, por exemplo, possui um nÃmero de cetano de 68,77 frente aos 52,10 do de soja e 48 do Ãleo diesel mineral. Jà o biodiesel de mamona possui viscosidade de 14,5 cSt, frente aos 4,16 do de soja e 2,5 do Ãleo diesel mineral. Espera-se que essas caracterÃsticas singulares tenham consequÃncias importantes nos processos de injeÃÃo, atomizaÃÃo e queima do combustÃvel. O objetivo deste trabalho à determinar a extensÃo dessas consequÃncias, caracterizando-se o impacto de cada um desses biodieseis de segunda geraÃÃo sobre a taxa aparente de liberaÃÃo de energia. Empregou-se, para tanto, dados experimentais de pressÃo no cilindro e um modelo de anÃlise de liberaÃÃo de calor, ou de energia, com uma zona de combustÃo. Os dados foram obtidos com um motor diesel turbo de mÃdio porte operando em condiÃÃes de regime permanente e a trÃs nÃveis de carga. Preparou-se misturas entre diesel e biodiesel nas concentraÃÃes B10, representativas do patamar atual de adiÃÃo de biodiesel ao diesel mineral, e B20, que corresponderiam à maior adoÃÃo de biocombustÃveis em um cenÃrio futuro. As matÃrias-primas de segunda geraÃÃo, sebo bovino e mamona, tambÃm foram comparadas a dados obtidos com o biodiesel de Ãleo de soja, que corresponde a cerca de 75% a atual produÃÃo brasileira de biodiesel. Para as misturas B20, constatou-se que o biodiesel de sebo bovino, por ter maior nÃmero de cetano, adianta a combustÃo em cerca de 1◦ com relaÃÃo ao de soja e 3◦ com relaÃÃo ao diesel mineral. Devido a este adiantamento da igniÃÃo, o biodiesel de sebo bovino tambÃm reduziu a quantidade de combustÃvel consumido pelo modo prÃ-misturado. A combustÃo das misturas contendo biodiesel de mamona ficou praticamente inalterada para as condiÃÃes de alta e mÃdia carga com relaÃÃo ao Ãleo diesel mineral. Contudo, em baixa carga (bmep=250 kPa) e na concentraÃÃo correspondente a B10 e B20, o biodiesel de mamona provocou um atraso expressivo na combustÃo, provavelmente devido à colisÃo do jato combustÃvel com as paredes do pistÃo.

In this thesis, it is shown how the Linux system was ported to the second generation wireless open access research platform (WARPv2) board. The purpose of the port was to extend the features of the WARPv2 board by producing a versatile standalone system that allows to run custom software on it. The Linux enriched design in WARPv2 also offers a controllable communication system by implementing all layers of the network architecture. Linux was chosen for the operating system for this work, because it is open source, which means it is easy to modify for different purposes. Moreover, Linux is well documented and it has wide software support. The Linux system was combined with the radio communication system provided by Rice University, USA. The field-programmable gate array (FPGA) hardware design was created for this combination and needed software of the system was defined and implemented. The developed system consisted of the Linux side and the MAC side. These sides implemented all layers of the network architecture. Both sides employed a dedicated processor core of the FPGA. Interprocessor communication between Linux and MAC sides was implemented to allow Linux to control the whole system. Two Linux kernel drivers were written to use interprocessor communication hardware. The setup process of the developed system was mitigated by writing several scripts. The developed system was tested, verified and analyzed to confirm that the implementation is valid and consistent. Several test cases were created for this purpose. Test cases were divided into two parts: hardware tests and performance tests. Hardware tests verified that the FPGA hardware design of the system was workable and fulfilled the requirements. Performance tests confirmed that the performance of the system was sufficient
Tässä työssä sovitettiin Linux-järjestelmä langattomalle kehitysalustalle (WARPv2). Sovitus tehtiin, jotta kehitysalustasta saataisiin monipuolinen ja itsenäinen. Lisäksi sovitus mahdollisti omien ohjelmien ajon alustalla sekä verkkoarkkitehtuurin kaikkien kerrosten hallittavuuden. Linux valittiin tämän työn käyttöjärjestelmäksi, sillä sen lähdekoodi on avoimesti saatavilla ja täten helposti muokattavissa eri tarkoituksiin sopivaksi. Linux on myös hyvin dokumentoitu ja sille on saatavilla runsaasti sovelluksia. Linux-järjestelmä yhdistettiin yhdysvaltalaisen Ricen yliopiston kehittämään langattomaan tiedonsiirtototeutukseen. Kehitysalustan FPGA-piirille suunniteltiin tälle yhdistelmälle sopiva laitteistototeutus ja tarvittavat ohjelmistot määriteltiin ja liitettiin mukaan järjestelmään. Kehitetty järjestelmä koostui Linuxosasta ja MAC-osasta. Nämä osat toteuttivat verkkoarkkitehtuurin kaikki kerrokset. Molemmille osille oli osoitettu oma suoritin FPGA-piiriltä. Linux- ja MAC-osan välille toteutettiin tiedonvälitysmekanismi, jotta Linux kykenisi hallitsemaan koko järjestelmää. Lisäksi Linuxille kirjoitettiin kaksi laitteistoajuria Linux- ja MAC-osien välisen tiedonvälityksen mahdollistamiseksi. Järjestelmän käyttöönoton helpottamiseksi kirjoitettiin useita komentosarjoja. Kehitetty järjestelmä testattiin, todennettiin ja analysoitiin järjestelmän toimivuuden varmistamiseksi. Testausta varten kehitettiin useita testitapauksia. Testaus koostui kahdesta osasta: laitteistotestauksesta ja suorituskykytestauksesta. Laitteistotestauksessa todennettiin laitteiston vaatimusten mukainen toiminta, kun taas suorituskykytestaussa varmistettiin suorituskykyvaatimusten täyttyminen

In the last years, Silicon becomes one of the most important technological platform for integrated photonics technologies. Nonlinear silicon photonics is a desired upgrade of this thecnology as it gives the opportunity to directly process the signal on the chip by using the wide spectrum of nonlinear phenomena. To have access to high order nonlinearities a large optical pump power is needed. Second order nonlinear effects are desirable due to the reduction of the used power with respect to third order nonlinearities. Moreover, it allows to achieve interesting efforts, such as wavelength conversion and generation of quantum states. Here the problem is that silicon has a diamond crystalline structure. Therefore, silicon is a centrosymmetric material. For a geometrical point of view, this property is reflected in a symmetry of the polarization vector P(E) = -P(-E) . The polarization vector is related to the electric field by: P = P^0 + P^(2) + P^(3) +... From equation 2, it is possible to see that, in order to respect the centrosymmetry, chi^(2) =0. So, in the dipole approximation, second order nonlinearities are inhibited in Silicon. Many efforts have been spent to induce second order nonlinearities in Silicon. At first, strained silicon, in which the centrosymmetry of Silicon crystalline structure is broken by an inhomogeneous strain, seemed to be the most viable solution. In strained silicon waveguides, the inhomogeneous strain is applied by a stressing layer of different materials with a different lattice constant deposited on top of the waveguide [4]. The first experiment based on Silicon waveguides was performed in 2006 by Jacobsen et al. that measured a nonlinear coefficient chi^(2) = 15 pm/V with a SiN stressing layer via DC electro-optic effect. This work was followed by many others, reaching values for the strain-induced second order nonlinear coefficient chi^(2) up to 340 pm/V. Few works gave a different interpretation of the chi^(2). It was demonstrated that during the deposition of the stressing layer there is the formation of dangling bonds at the interface between the deposited layer and the silicon waveguide. These dandling bonds act as positive fix ions. The formation of this charges, indeed, determined an abundance of free-carriers in the core of the waveguide that, because of the free carrier dispersion, can affect the value of the effective measured nonlinear coefficient in the DC electro-optic effect. Azadeh et al. demonstrated for the firs time the crucial role of this phenomenon which overtakes the strain effect, also confirmed by Olivares et al. An upper limit of chi^(2) = 8 pm/V due to a strain effect was experimentally fixed. Other works investigated second order nonlinearities in Silicon looking at the Second Harmonic Generation (SHG). Cazzanelli et al. measured a value of chi^(2) = 40 pm 30 pm/V by SHG in multimodal waveguides using a pump wavelength above 2 um, without any phase matching mechanism. It was also demonstrated that stressing layers that induced the same value of strain but realized with different materials yield different SHG, making clear that not only strain but also charged defects play an important role in the generation of the SH signal. Indeed, it was demonstrated that charged defects can induce an electric DC field that interacts with the large chi^(3) of bulk silicon to give a dressed (effective) second order nonlinear coefficient chi^(2)_EFISH = 3 chi^(3) E_DC via electric-field-induced second harmonic (EFISH) generation. So in 2017 the effect of the strain on silicon waveguides was not clear. The aim of my PhD work is try to understand the origin of the dressed chi^(2) in silicon waveguide and propose a way to engineer and control it. In order to understand the origin of second order nonlinearities in silicon, an experiment that can separate the role of the strain and the role of the trapped charged defects at the interface between the silicon waveguide and the stressing layer in an unambiguously way was performed. The sample used was composed by a set of strip silicon waveguides 243 nm thick with a SiN stressing layer of 140 nm deposited on the top of the waveguide. The waveguides were engineered in order to have intermodal phase matching condition between the TM1 mode for the pump wavelength and TE3 mode for the generated SH wavelength. Different widths of the waveguide have been used in order to tune the phase-matching condition wavelength. To investigate the role of the strain, the sample was mounted on a sample holder equipped with a screw to deformed the waveguide. Rotating the screw, a vertical displacement Delta_H is induced in the center of the sample orthogonal to its main plain. This displacement acts as an external load that increase the strain in the silicon waveguide. SHG was measured for different values of the Delta_H displacement. Increasing the load in the sample there is a red-shift of peak. Indeed, increasing the strain in the sample a change in the effective index is induced, and a change in the phasematching condition is obtained. However, SH power is always the same, revealing that the value of chi^(2) is not increasing with the strain. To investigate the role of the trapped defect at the Si/SiN interface, following the idea of Piccoli et al., the sample was exposed to UV irradiation to induce a passivation (i.e. neutralization) of the defects. Then, SHG was measured and no generation can be detected. These results clarify that the main causes of the SH in silicon waveguide is not given by the strain but by the charge defect and an upper limit of chi^(2) at 0,05 pm/V for the strain induced second order nonlinear coefficient was experimentally fixed. This result is also supported by an earlier theoretical estimation given by Khurgin et al. in 2015. From these observations, the use of an applied electric field emerges as a way to induce a controlled effective chi^(2) in silicon waveguide suitable for technological application. The idea is based on the use of a controlled external E_DC field in order to obtain the desired value of chi^(2) where the electric field can be generated by placing lateral p-i-n junctions across the waveguide that can be reverse biased using metallic pads. In this way, chi^(2) can be enhanced increasing the applied bias and the only limitation is the breakdown field of silicon, that is known to be around V = 24 V. Timurdogan et al. demonstrated that it is also possible to use the periodicity of the p-i-n junctions to absorb the mismatch between the pump and the SH modes in order to obtain a quasi-phase matching condition. The sample used was a set of rib waveguides with different widths. Along the propagation direction of the waveguide p-i-n junctions have been grown. Since in the generation efficiency what matters is not the overall chi^(2) but the amplitude of its oscillations along the length of the waveguide, an interdigitated poling configuration was studied. In this configuration, regions of p-i-n junctions and regions of n-i-p junctions are periodically alternated. Second harmonic generation was observed in this poled waveguide and the SH signal increased quadratically with both the pump power and the applied bias, according with the theory. It was also demonstrated that a larger conversion efficiency is obtained using this poling configuration instead of the poling configuration proposed by Timurdogan in 2017. Also a modeling of the effect of the fabrication defects has been done. The pump P_p and the generated P_SH powers are related by P_SH = P_p^2|gamma^(2)|^2 L^2 S where S is the poling therm which describes what is happening along the length of the waveguide. S is a function of the geometry of the waveguide and of the periodicity of the p-i-n junctions: S=1/L^2 |int_0^L s(z) exp(i Delta beta z) dz|^2. During the fabrication, an unwanted variation of the geometrical parameters can be induced along the length of the waveguide both in the waveguide cross section and in the poling period. The effect of this two kind of variations has been studied. Moreover, the coherence length of the process has been also studied, in order to have a clear understanding of the EFISH process. the developed model was compared with the experimental data. It is possible to extract the effective Delta chi^(2) of the EFISH process with an interdigitated poling configuration, when 24 V are applied to the junctions: Delta chi^(2)_eff=78 pm 3 pm/V. Finally it was perform a study of microrings that can accomodate geometrical defects. Using a 4-bar symmetry of the chi^(2) tensor, a study of the conversion efficiency as a function of the different parameters of the microring has been performed. It was demonstrated that the most critical parameter is the thickness of the waveguide in the ring and it was shown a method to find a geometry that allows to have efficient conversion efficiency in a range of thickness of 16 nm around the nominal value. Moreover, this method is more general, since it is based only on the symmetry of the nonlinear tensor. Therefore, it can be easily applied to other materials.

Ten Jewish second-generation men and women from metro Portland, Oregon were interviewed regarding growing up in the aftermath of the Holocaust. The American-born participants ranged in age from fifty-one to sixty-four years of age at the time of the interviews. Though the parents were deceased at the time of this study the working definition of a Holocaust survivor parent included those individuals who had been refugees or interned in a ghetto, labor camp, concentration camp, or extermination camp as a direct result of the Nazi Regime in Europe from 1933 to 1945. A descriptive phenomenological approach was utilized. Eight open-ended questions yielded ten unique perspectives. Most second-generation do not habitually inform others of their second-generation status. This is significant to conflict resolution as the effects of the Holocaust are trans-generational. The second-generation embody resilience and their combined emphasis was for all people to become as educated as possible.

Immigrant entrepreneurship is defined as business establishment and ownership among immigrants who arrive to a new host country. Immigrant entrepreneurship has become an important theme due to the increasing rates of immigration to developed countries, and its impact on their economic development. However it is also discredited and qualified as low value-added, rarely innovative, restricted to the ethnic communities and with stagnating growth potential. Following this debate, a new research stream affirms that immigrants should not be treated as one entity. Thus attention is shifting towards groups of immigrant entrepreneurs that were previously neglected in the literature. One such group consists of the second generation children of immigrants. Work to date provides ample investigation about immigrant entrepreneurs and their entrepreneurial process; however there is less research on similarities and differences in the entrepreneurial process experienced by first and second generation immigrant entrepreneurs. Despite some recent research on second generation immigrant entrepreneurs, this topic remains understudied. The objective of this study is to understand, from a multi-level perspective, how different generations of immigrant entrepreneurs experience the entrepreneurial process. Using a grounded theory approach and qualitative in-depth interviews, the findings indicate that first and second generation immigrant entrepreneurs experience the entrepreneurial process differently by facing different micro and macro level enablers and obstacles. They also recognize, evaluate and exploit opportunities differently. The extent to which they are embedded in specific environments affects their entrepreneurial experiences.

In recent years, it has been proposed that circular microresonators may become an important element in the core of many photonic devices. The high Q-factors seen in fused silica micro-spheres and micro-toroids for light coupled in the whispering gallery modes (WGMs) inside the micro-resonator led to many new developments in a diversity of fields. Indeed, WGM micro-resonators have found applications in laser oscillation, optical filtering, bio and chemical sensing, frequency stabilization, quantum electrodynamics experiments, nonlinear parametric conversion and in many other light-matter interaction processes where light recirculation is an essential ingredient. For second and third order nonlinear optical phenomena a high-Q micro circular cavity is an ideal framework to lower the light intensity or material density and still obtain a measurable interaction. This may become particularly useful when the nonlinear interaction is considered on the sphere surface because at an interface centro-symmetry is always broken. In this thesis, we approach the problem of obtaining SHG with the smallest amount of material possible. Our goal is to demonstrate that WGMs in micro-sphere resonators are an optimal option to consider such type of non-linear interaction. SHG from a small amount of material may found interesting applications in high sensitivity unmarked detection of low numbers of very small objects such as molecules, viruses or other types of nano-particles. The different experimental and theoretical developments we implemented to achieve such goal are reported in the four chapters of the current thesis. In chapter 1 we introduce basic concepts of spherical micro-resonators an their interest. Theoretical aspects of light propagation and nonlinear light generation in the whispering gallery modes in such micro-resonators are discussed in Chapter 2. A new method to obtain patterns of non-linear material is presented in Chapter 3. In Chapter 4, the developments presented in the previous chapters are combined to obtain second harmonic generation in the whispering gallery modes of microspheres. In this chapter we report the design and fabrication of a nonlinear spherical resonator to experimentally measure SHG from molecules deposited on its surface. Such nonlinear interaction is quasi-phase matched by implementing the periodical patterning reported in Chapter 3 on a molecular layer deposited on the surface of a micro-sphere. By coupling laser light pulses at the fundamental frequency into the whispering gallery modes of the high-Q spherical micro-resonators we demonstrate that a signal at the second harmonic (SH) frequency can be measured when less than 100 molecules contribute in the nonlinear interaction. Finally, applications of such type of generation in highly sensitive sensing are discussed.
En años recientes los microresonadores circulares han sido propuestos como un elemento central para formar parte de muchos dispositivos fotónicos. El alto factor de calidad observado en microesferas o microtoroides de sílice cuando la luz se propaga en modos "whispering gallery" (WG) ha dado lugar a un gran número de nuevos desarrollos en campos muy diversos. En efecto, los micro resonadores con modos WG han encontrado aplicación en la oscilación laser, en el filtrado óptico, en sensores bioquímicos, como estabilizadores de frecuencia, en experimentos de electrodinámica cuántica, en la conversión paramétrica no lineal y en muchas otros procesos donde la recirculación de luz es un ingrediente esencial para su interacción con la materia. En fenómenos ópticos no lineales de segundo y tercer orden, la micro cavidad circular con un alto factor de calidad constituye una estructura ideal para poder obtener una interacción medible incluso cuando se consideran pequeñas intensidades de luz o bajas densidades de materia. Esto puede resultar particularmente útil en la superficie de la microesfera ya que en la interface entre dos materiales se rompe la simetría de inversión incluso cuando los materiales son centro simétricos. En esta tesis abordamos la generación de segundo armónico con una cantidad mínima de material. Nuestra meta es demostrar que los modos WG en resonadores de microesfera son una opción óptima para poder considerar este tipo de interacción no lineal. La generación de segundo armónico con una cantidad muy pequeña de material puede encontrar aplicaciones interesantes en la detección de muy pocos objetos pequeños tales como moléculas, viruses o cualquier otro tipo de nanopartículas. Los diferentes desarrollos experimentales y teóricos que implementamos para alcanzar nuestro objetivo están explicados en los cuatro capítulos de esta tesis. En el Capítulo 1 introducimos conceptos básicos de microresonadores esféricos y su interés. Aspectos teóricos de la propagación y generación no lineal de luz de los modos WG en dichos resonadores se discuten en el Capítulo 2. Un método nuevo para generar patrones de material no lineal se presenta en el Capítulo 3. En el Capítulo 4, los desarrollos de los capítulos previos presentados se combinan para implementar la generación de segundo armónico en los modos WG de las microesferas. En este capítulo reportamos el diseño y la fabricación del resonador esférico no lineal para llegar a medir experimentalmente la generación de segundo armónico de las moléculas depositadas en su superficie. Dicha interacción no lineal se obtiene en la configuración "quasi-phase matched" implementando el mecanismo de escritura de patrones reportado en el Capitulo 3, sobre una capa molecular depositada en la superficie de la microesfera. Mediante el acoplamiento de pulsos de luz láser a la frecuencia fundamental en los modos WG de un microresonador esférico con un alto factor de calidad Q, demostramos que la señal a la frecuencia de segundo armónico puede ser medida, menos de 100 moléculas contribuyen a esta interacción no lineal. Finalmente, se discuten aplicaciones de ese tipo de generación para la detección altamente sensible.

Studies have been undertaken to utilise the possible potential of the rodlike, helical structures associated with polyglutamates and polyisocyanates for piezoelectric (PE) and nonlinear optical (second harmonic generation (SHG)) applications. Various techniques have been employed to form samples/films of these polymers containing oriented helices whose bulk structures are non-centrosymmetric, (an important criterium for the aforementioned applications). Owing to the poor yields obtained for certain intermediates in the synthetic stages of these polymers, only poly('S-benzyl-L-glutamate) (PBzLG) and poly(n- hexylisocyanate) (PHIC) were available for subsequent studies. Piezoelectric work was limited to hydrostatic measurements (d3h) made on electrically poled, composite (guest host), polymer samples. Phase separation was common in all the samples, but no piezoelectric response was observed. However, low concentration (not greater than 10% w/w) of active polymer (PBzLG or PHIC) and high conductivity during the poling stage, may have accounted for the lack of response. Electrically poled, homopolymer samples of PBzLG and PHIC were achieved using a solvent evaporation technique. Nonlinear optical studies of these poled samples revealed threshold fields above which detectable levels of SHG could be observed, (i.e. PBzLG > 40 V/mm, PHIC > 150 V/mm). The variation of SHG signal versus the angle of polarisation of the incident laser light (1064 nm) relative to the poling direction of the film, implied biaxial symmetry was present in the case of PBzLG, whereas the more conventional uniaxial symmetry was observed for PHIC. The variation in SHG signal observed for a fixed thickness was attributed to varying degrees of alignment, resulting from uneven poling. Although PHIC and PBzLG showed low SHG activity (less than value for urea), little ageing of this activity occurred over the 6 month testing period. Langmuir Blodgett studies carried out on chemically modified, low molecular weight PBzLG molecules showed poor transference of the monolayer to a quartz substrate once ten layers had been deposited. In addition, areas per molecule (or per residue) calculated from the pressure-area isotherms, proved inconclusive when deducing possible orientations for the PBzLG helices. No SHG signal was observed for the L.B. films.

Many expert, or knowledge-based, systems have been constructed in the domain of ecology, several of which are concerned with habitat evaluation. However, these systems have been geared to solving particular problems, with little regard paid to the underlying relationships that exist within a biological system. The implementation of problem-solving methods with little regard to understanding the more primary knowledge of a problem area is referred to in the literature as 'shallow', whilst the representation and utilisation of knowledge of a more fundamental kind is termed 'deep'. This thesis contains the details of a body of research exploring issues that arise from the refinement of traditional expert systems methodologies and theory via the incorporation of depth, along with enhancements in the sophistication of the methods of reasoning (and subsequent effects on the mechanisms of communication between human and computer), and the handling of uncertainty. The approach used to address this research incorporates two distinct aspects. Firstly, the literature of 'depth', expert systems in ecology, uncertainty, and control of reasoning and related user interface issues are critically reviewed, and where inadequacies exist, proposals for improvements are made. Secondly, practical work has taken place involving the construction of two knowledge based systems, one 'traditional', and the other a second generation system. Both systems are primarily geared to the problem of evaluating a pond site with respect to its suitability for the great crested newt (Triturus cristatus). This research indicates that it is possible to build a second-generation knowledge-based system in the domain of ecology, and that construction of the second generation system required a magnitude of effort similar to the firstgeneration system. In addition, it shows that, despite using different architectures and reasoning strategies, such systems may be judged as equally acceptable by endusers, and of similar accuracy in their conclusions. The research also offers guidance concerning the organisation and utilisation of deep knowledge within an expert systems framework, in both ecology and in other domains that have a similar concept-rich nature.

Interest in entrepreneurship has increased in the past few years as more schools are beginning to incorporate subject and degrees specializing in the area as well as individuals mobilizing into an entrepreneurial lifestyle due to the lack of opportunities in the standard workplace environment. Historically, immigrants have made up a large majority of entrepreneurs and it has been their primary way of upward mobility in society. The boom in high tech start-ups and other small businesses in the last decade have primarily been driven by children of immigrants. As a result of these recent trends this study analyses the foreign born children of immigrants and their entrepreneurial capacity. The intent of this study is to find to what extent human capital affects the entrepreneurial capacity of immigrant children, if any. By analyzing the Theory of Human Capital in Entrepreneurship and its main variables, the study aims to find their level of human capital. Through the gathering of recent population data, analysis of research journals, publications and books, we evaluate the level of human capital and how it affects the capacity of the individual. Historically, evidence has shown a correlation between the two and we hope to contribute to the research and better understand its role in our subject matter as well as bring more awareness to a topic that lacks information.
B.S.B.A.
Bachelors
Business Administration
Management

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The design and construction of an Autonomous Underwater Vehicle (AUV) for use as a research and development testbed at the Naval Postgraduate School (NPS) is presented. Design objectives, analysis and trade-offs are discussed with respect to a generic AUV and specifically detailed for the case of the NPS AUV II. System integration and flexibility is emphasized in the subject vehicle to support presently planned and future research employment. Hull, mobility, sensor, automatic control, and energy subsystemsl are described. Design and fabrication techniques for the NPS AUV II vehicle hull and equipments are documented

Les fibres optiques en tant que milieux centro-symetriques ne devraient pas, normalement, produire un rayonnement de second harmonique. Cependant, des rendements de doublage de frequence de l'ordre de 5% peuvent etre obtenus dans des fibres de silice dopees au ge. Cet effet remarquable fait actuellement l'objet d'un grand nombre de recherches. Des rendements non negligeables de second harmonique sont d'un grand interet technologique, ce processus pouvant a terme remplacer les tres onereux cristaux conventionnels doubleurs de frequence. Stolen et tom ont montre que le temps necessaire pour obtenir un rendement de conversion important peut etre considerablement reduit en procedant a une premiere etape de preparation, au cours de laquelle la fibre est irradiee simultanement a 1064 nm et 532 nm (phase d'ecriture). Recemment baranova, zel'dovich & al. Ont propose un modele microscopique qui pourrait expliquer la formation d'un reseau holographique de dipoles orientes detruisant localement la symetrie d'inversion et dont la periode correspond exactement aux conditions d'adaptation de phase pour la generation du second harmonique. Nous avons etudie l'influence de divers parametres experimentaux (dopage des fibres optiques, duree et largeur spectrale des impulsions, puissance crete injectee, proportion de rayonnement de second harmonique injectee lors de la phase de preparation) sur deux phenomenes de saturation intervenant lors de la generation de second harmonique dans les fibres optiques: la saturation avec l'energie injecte lors de la phase de preparation et la saturation avec la longueur de la fibre (longueur effective du reseau holographique). Les resultats obtenus sont dans l'ensemble en bon accord avec les previsions theoriques du modele de zel'dovich et les hypotheses microscopiques suggerees quant a l'origine des centres responsables de la formation du reseau holographique (centre ge(1)). Comme exemple d'application technologique de ce phenomene nous montrerons que le rayonnement de second harmonique genere par une fibre optique permet le pompage synchrone d'un laser a colorant

This study explores the engagement with music among second-generation migrants in Sweden in connection to their cultural identity and sense of belonging. First, a theoretical frame is developed that illustrates how music practices can contribute to the creation of ‘sense of place’ and ‘sense of belonging’ and how they are linked to ‘collective memory’ and ‘cultural identity’. Consequently, it is also explained how all this can be understood from a ‘generational perspective’. A qualitative approach has been chosen for this study and semi-structured interviews with 9 emerging adults living in Sweden, were conducted. The main results show that there is a high engagement with music among second-generation migrants in Sweden, many of them possessing a broad repertoire of favorite songs and genres. Mainly, it is through listening to the music coming from the home countries of their parents that they can express and navigate their cultural identities. Such kind of music carries meanings and mediates collective experiences and memories which can be passed on from one generation to the next one. These practices are important for second-generation migrants in terms of their sense of belonging to certain groups with which they can identify and feel connected to. In this sense, such kind of music helps them make sense of themselves in the world and in connection to others.

Electrochemical oxidation of metal electrodes in aqueous media has been examined by in situ optical second harmonic generation (SHG), a nonlinear optical technique of second order. Simultaneous SHG and cyclic voltammetry experiments were carried out on Cu electrodes in alkaline media. The SHG response was found to be sensitive as Cu was oxidised first to Cu2O and then to CuO. The formation of Cu2O causes resonant contribution to the SHG signals due to the band-gap of Cu2O. As the upper layer, CuO is formed; it generates an electric-field induced second harmonic (EFISH) response. When the oxides layers are reduced, the SHG intensity changes markedly. The correlation of oxidation and reduction charge with the SHG signal intensity is found to be a useful method to investigate the oxide formation. The oxidation of Au electrodes in acidic media has been investigated. The initial growth of the compact (or α-) oxide causes a decrease in SHG intensity which is suggested to be the effect of the oxide growth on surface plasmons originated from the d-electrons in Au. When the thicker hydrous (or β-) oxide layers are formed at constant potentials on top of the α-oxide, the reductions of them are accompanied by remarkable sharp peak in the SHG response that appear just before any reduction charges begin to pass. As the β-oxide layer gets thicker with longer oxidation time and then reduced, the initial peak evolves into two before merging to form one broad peak. The SHG peaks are suggested to be linked to an order-disorder transition phenomenon at the α-/β-oxide interface; or it can also be due to the presence of the surface traps. These investigations have shown that the SHG technique with its inherent submonolayer sensitivity can be a useful technique to study electrochemical oxidation of metal electrodes.