Free-electron lasers (FELs) are among the world's most intense artificial artificial sources of coherent light and are tunable to various wavelengths, including the X-ray spectrum. X-ray FELs (XFELs) are extremely useful for diffraction experiments to study molecules, materials, and quantum systems. A FEL consists of an electron accelerator and a structure of magnets called an undulator. The undulator has a periodic magnetic field, and when an electron beam passes through the undulator, the Lorentz force forces the electrons to oscillate and emit what is known asspontaneous undulator radiation. Initially, the undulator radiation is spontaneously emitted and incoherent. However, aAs the electrons interact with this initial spontaneous undulator radiation, they change their relative positions and form micro-bunches of electrons. These microbunches are shorter than the undulator radiation wavelength. Hence, the waves emitted by the electrons from the same microbunch arethey become in phase, meaning the radiation is now coherent with the radiation field, and the state of coherence develops. This process is known as self-amplified spontaneous emission (SASE). Due to the coherence, tThe radiation intensity grows exponentially along the undulator, forming several peaks in the radiation pulse known as SASE spikes. One technique for obtaining ultra-short laser pulses is to isolate single SASE spikes by controlling where, along the electron beam, the SASE spikes can grow. This growth limitation is archieved by modulating the electron energies, thus only allowing electrons at specific positions along the electron beam to radiate. In addition, to keep positive interference between undulator radiation from electrons with different energies, the energy modulation must be compensated with a gradient of the magnetic field amplitude of the undulator, so-called tapering. There are plans to implement this technique at one of the beamlines at the European X-ray FEL (EuXFEL) to generate attosecond X-ray pulses and study quantum systems. One goal of the design process is to choose design parameters for the electron beam's modulation amplitude and the undulator's tapering coefficient. These design parameters shall be chosen so that the XFEL will have as short pulse duration as possible while at the same time not getting too low peak power. This thesis aims to study the effect of electron energy modulation and undulator tapering on the SASE and how the modulation amplitude and the tapering coefficient affect the XFEL's peak power and pulse duration. A model was developed to simulate SASE with a modulated electron beam in a tapered undulator. With this model, a parameter scan gave the average peak power and pulse duration as functions of the modulation amplitude and the tapering coefficient. The parameter scan showed that the peak power and the pulse duration decrease as the modulation amplitude and the tapering coefficient increase. Therefore, a trade-off exists between high peak power and short pulse duration. It was possible to exclude sets of the parameters that gave too low peak power or long pulse duration. This study also found an optimum range for the tapering coefficient where the peak power had a local maximum without a significant increase in pulse duration. The physics behind this optimal tapering coefficient is also discussed in connection to the electrons' energy modulation.

No description available.

研究背景與目的：2008年美國睡眠醫學會(American Academy of Sleep Medicine)對於失眠患者在助眠劑的臨床使用原則中(clinical guideline)，建議初次藥物治療的時間以2至4週較為適宜，後續是否繼續用藥則須專業醫師的重新評估，以降低身體對於藥物的依賴性及副作用的風險，但實際上許多失眠患者因擔心停用助眠劑就無法入眠，因此仍長期使用助眠劑。目前臨床上大都採用逐步減藥的方式協助患者降低助眠劑的使用，除了藥物因素會影響減藥成效之外，從心理因素來看，在過去研究指出自我效能會影響健康行為的改變，因此本研究將比較逐步減藥計畫加上提升減藥自我效能策略與單獨逐步減藥計畫對於原發性失眠患者在減藥上的成效。 研究方法：本研究的原發型失眠患者共48人(男17人，女31人，平均年齡46.8歲，平均使用助眠劑66.7個月)，被分為兩組進行10週的減藥介入計畫，一組為自我效能提升組(n=24)，受試者減藥前先接受為期兩週的提升減藥自我效能策略，再進行8週的逐步減藥計畫，另一組為單純減藥組(n=24)，受試者只進行8週的逐步減藥計畫。受試者每週均需填寫睡眠日誌、單題減藥自我效能量尺，以瞭解睡眠參數、減藥自我效能及助眠劑使用之情況。 研究結果：減藥成效方面，自我效能提升組在減少劑量的百分比顯著高於單純減藥組(自我效能提升組=78.62%；單純減藥組=64.10%)，且自我效能提升組在減藥前後劑量的改變也顯著高於單純減藥組(自我效能提升組=4.35顆/週；單純減藥組=3.22顆/週)，自我效能提升組在停藥人數的百分比上雖未顯著高於單純停藥組(自我效能提升組=29.2%；單純減藥組=16.7%)，但就整體結果來看均較為支持自我效能提升組在減藥的成效上是優於單純減藥組。減藥自我效能方面，在控制住第1週的減藥自我效能後，提升減藥自我效能策略造成的減藥自我效能改變量仍可以有效解釋21.9%的減藥百分比。 研究結論：自我效能提升組增加的提升減藥自我效能策略能有助於個案在執行逐步減藥計畫的成效，另外，提升減藥自我效能策略造成的減藥自我效能改變量是減藥百分比有效的預測因子。因此，減藥自我效能對於減藥成效來說，確實是一個可以著力的部分。 / Introduction：According to the 2008 clinical guidelines for insomnia by the American Academy of Sleep Medicine proposed, hypnotic use is recommended for short-term use for 2 to 4 weeks. However, many insomnia patients have difficulty to stop hypnotic use. In clinic practices, gradual tapering is usually applied in helping patients to reduce the hypnotic use. Previous studies have shown that self-efficacy of the patients are associated with medication tapering. The present study examine the effect of the institution of a self-efficacy enhancement strategy prior to gradual tapering plan on hypnotic tapering in patients with primary insomnia. Methods：Forty-eight patients with primary insomnia (17 men, 31 women；mean age of 46.8 years；mean duration of hypnotics use of 66.7 months) were assigned to two groups: a self-efficacy enhancement group and a tapering group. Patients in the self-efficacy enhancement group (n=24) underwent a two-week self-efficacy enhancement strategy prior to an eight-week gradual tapering plan. Patients in the tapering group (n=24) participated in the eight-week gradual tapering plan only. The main outcome measures were sleep parameters from sleep diary, a single-item tapering self-efficacy rating scale, number of pills taken per week, and percentage of dosage reduction. Results：The percentage of dosage reduction of patients in the self-efficacy enhancement group was significantly more than those in the tapering group (the self-efficacy enhancement group = 78.62%；the tapering group = 64.10%). The number of pills taken per week also showed significantly more reduction for patients in the self-efficacy enhancement group than those in the tapering group (the self-efficacy enhancement group = 4.35 pills per week；the tapering group = 3.22 pills per week). However, the percentage of drug-free patients at the end of the programs in the self-efficacy enhancement group was not significant different from those in the tapering group (the self-efficacy enhancement group = 29.2%；the tapering group = 16.7%). Overall, the effect of hypnotic tapering in the self-efficacy enhancement group was better than those in the tapering group. In addition, linear regression showed that the tapering self-efficacy data showed that, after controlling baseline tapering self-efficacy, the change of tapering self-efficacy following the first two weeks of self-efficacy enhancement strategy can explain the variation of percentage of dosage reduction up to 21.9%. Conclusions：The institution of self-efficacy enhancement strategy can increase the efficacy of gradual tapering plan for hypnotics. In addition, the level of tapering self-efficacy enhanced by the self-efficacy enhancement strategy is a good predictor for dosage reduction. This is a useful strategy that can be applied in clinical settings.

Este estudio analizó los cambios en variables cardiorrespiratorias, neuromusculares, hormonales, de composición corporal y de rendimiento en un grupo de 18 kayakistas varones de elite mundial durante una temporada completa de entrenamiento concurrente de 43 semanas, una fase de puesta a punto de 4 semanas así como los efectos de un periodo de desentrenamiento de 5 semanas en los grupos de cesión total de entrenamiento (CE) y de reducción parcial de entrenamiento (RE). El volumen y la intensidad de entrenamiento fueron cuantificados a nivel individual durante todas las fases del estudio. Un control exhaustivo sobre las variables que definen el programa de entrenamiento permitió alcanzar adaptaciones positivas tanto en las variables de fuerza como en las de resistencia durante un programa de entrenamiento concurrente en deportistas de élite mundial. Así mismo, periodos cortos de CE produjeron mayores descensos del rendimiento neuromuscular y cardiorrespiratorio comparado con la estrategia de RE. / This study was undertaken to analyze changes in selected cardiovascular, neuromuscular, hormonal, body composition and performance variables in a group of 18 male elite kayakers across an initial concurrent training program of 43-wk, a 4wk tapering phase, as well as the effects of a subsequent detraining period of 5-wk under reduced training (RT) or training cessation (TC) approach. Training volume and exercise intensity were quantified for each subject throughout the study. An exhaustive control over the training program variables allowed to highly-trained athletes achieves positive adaptations in both cardiovascular endurance and muscle strength under a concurrent training regime. Likewise, short-term TC results in large decreases in neuromuscular and cardiovascular function compared with RE strategy.

Submitted by Luis Lellis (luislellis@gmail.com) on 2015-12-16T08:26:29Z No. of bitstreams: 1 O IMPACTO DA POLÍTICA MONETÁRIA NÃO CONVENCIONAL AMERICANA SOBRE O PREÇO DOS ATIVOS FINANCEIROS BRASILEIROS.pdf: 932868 bytes, checksum: 3f85c3ea92ee9a2a52647220f067a572 (MD5) / Approved for entry into archive by GILSON ROCHA MIRANDA (gilson.miranda@fgv.br) on 2016-01-25T17:49:43Z (GMT) No. of bitstreams: 1 O IMPACTO DA POLÍTICA MONETÁRIA NÃO CONVENCIONAL AMERICANA SOBRE O PREÇO DOS ATIVOS FINANCEIROS BRASILEIROS.pdf: 932868 bytes, checksum: 3f85c3ea92ee9a2a52647220f067a572 (MD5) / Approved for entry into archive by Maria Almeida (maria.socorro@fgv.br) on 2016-01-27T17:43:13Z (GMT) No. of bitstreams: 1 O IMPACTO DA POLÍTICA MONETÁRIA NÃO CONVENCIONAL AMERICANA SOBRE O PREÇO DOS ATIVOS FINANCEIROS BRASILEIROS.pdf: 932868 bytes, checksum: 3f85c3ea92ee9a2a52647220f067a572 (MD5) / Made available in DSpace on 2016-01-27T17:43:49Z (GMT). No. of bitstreams: 1 O IMPACTO DA POLÍTICA MONETÁRIA NÃO CONVENCIONAL AMERICANA SOBRE O PREÇO DOS ATIVOS FINANCEIROS BRASILEIROS.pdf: 932868 bytes, checksum: 3f85c3ea92ee9a2a52647220f067a572 (MD5) Previous issue date: 2015-05-26 / Aplicando uma metodologia de testes de eventos, este estudo avalia o impacto dos anúncios de implementação e retirada dos estímulos monetários pelo Banco Central americano (FED) entre 2008 a 2013 sobre a curva de juros, a taxa de câmbio e a bolsa brasileira. Os resultados mostram que os anúncios de política monetária americana impactaram o preço dos ativos brasileiros significativamente principalmente durante o QE1 e o Tapering. Para os demais QEs, Operação Twist e eventos de postergação da retirada de estímulos, o não Tapering, ainda que os resultados encontrados estivessem dentro do esperado, eles tiveram baixa significância. Concluímos que a política monetária americana não convencional foi eficaz em impactar o preço dos ativos brasileiros, em especial os eventos não esperados. Ao incluirmos defasagens nos testes aplicados concluímos que em alguns casos houve 'atraso' na incorporação das novas informações no preço dos ativos.

Made available in DSpace on 2016-03-15T19:37:43Z (GMT). No. of bitstreams: 1 Priscila Romagnoli.pdf: 2103605 bytes, checksum: 61f6314f8d7400988a432b7a4793d4be (MD5) Previous issue date: 2013-01-24 / Photonic crystal fibers have been proposed as single-polarization (or polarizing) fibers with important applications being demonstrated, for example, in telecommunications, sensing and georeferencing. Although the vast majority of reported studies have focused on the numerical analysis of the performance of PCFs with specific and unconventional designs, post-processing PCFs also allows for great flexibility in altering the characteristics of guidance. In this work, the structure of a commercial, highly birefringent, PCF, with different holes diameters, has been locally changed using a tapering technique, which reduces the transverse dimensions of the fiber, with the application of pressure in the holes. This process was implemented to create 1-cm-long sections with a 66% reduction in their cross-sectional dimensions, through the application of pressure using two different schemes. It is numerically and experimentally shown that the two resulting structures are polarizing. In the first scheme, the same pressure is applied to all holes, resulting in a polarizing PCF at a wavelength of 633 nm, with an experimentally obtained polarization extinction ratio (PER) of 6.44 dB. In the second scheme, the applied pressure was different for the large and small holes, resulting in a polarizing PCF for the 1510-1590 nm wavelength range, with an experimentally obtained PER of more than 30 dB. Both the simplicity of the method and the resulting PER compares favorably with alternative methods to create polarizing conventional and photonic crystal fibers. / Fibras de cristal fotônico (PCFs, do inglês photonic crystal fibers) vêm sendo propostas como fibras polarizadoras, com importantes aplicações sendo demonstradas, por exemplo, em telecomunicações, sensoriamento e georreferenciamento. Apesar da vasta maioria dos trabalhos reportados analisarem numericamente o desempenho de PCFs com designs específicos e não convencionais, o pós-processamento em PCFs comerciais permite grande flexibilidade na alteração das características de guiamento. Neste trabalho, a estrutura de uma PCF altamente birrefringente comercial, com capilares de diferentes diâmetros, foi alterada localmente utilizando uma técnica de afilamento (tapering), que reduz as dimensões transversais da fibra, com aplicação de pressão nos capilares. Este processo foi implementado para criar seções de 1 ���� de extensão com uma redução nas dimensões transversais de 66%, aplicando-se pressão de duas formas diferentes. Demonstra-se numérica e experimentalmente que as duas estruturas resultantes são polarizadoras. Na primeira forma, aplicou-se uma única pressão em todos os capilares, resultando em uma PCF polarizadora no comprimento de onda de 633 ����, com uma razão de extinção de polarização (PER) experimentalmente obtida de 6,44 ����. Já na segunda forma aplicaram-se pressões diferentes nos capilares grandes e pequenos, o que resultou em uma PCF polarizadora para a faixa de comprimentos de onda que se estende de 1510 ���� a 1590 ����, com uma PER experimentalmente obtida superior a 30 ����. Tanto a simplicidade do método quanto a PER resultante possuem resultados positivos em comparação a métodos alternativos para a produção de fibras convencionais e fibras de cristal fotônico polarizadoras.

No description available.

There has been a growing interest in economic policies and their impact within a country among the real estate economics research community in recent years. After the economic crisis of 2008, an unconventional monetary policy was created, and it has been called quantitative easing (QE), an instrument of economic policy applied through central banks to boost the economy in periods when conventional monetary policy is not satisfactory. As with the economic challenge brought by COVID-19, many central banks had to implement unconventional monetary plans. This thesis aims to discover the impact of quantitative easing (QE) and its opposite quantitative tapering (QT) on the housing prices of the US real estate market. In order to deal with this problem, this research performs time-varying rolling correlations, which are correlations between two-time series on a rolling window. The window for this research will be monthly and subject to historical data points from a 280-month period of the USA metropolitan price housing and the Federal Balance sheet between 1998 and 2022. The results show there is a positive correlation between the different US housing markets and the US Federal Balance Sheet in the majority of the US markets analyzed and finds a high positive correlation between the different regional house price indices and US National Home Price Index and finally the existence of spillover effect between the cities in the high tier (e.g., Los Angeles and Miami) and low-tier (e.g., Chicago and Atlanta) cities, such that rising trends in one city are mirrored by the following changes in the other city in the equivalent tier and vice versa. / Under de senaste åren har det funnits ett växande intresse för ekonomisk politik och dess inverkan inom ett land bland den fastighetsekonomiska forskarvärlden. Efter den ekonomiska krisen 2008 har en okonventionell penningpolitik skapats och den har kallats kvantitativa lättnader (QE); ett ekonomiskt politiskt instrument som tillämpas genom centralbanker för att stärka ekonomin i perioder då den konventionella penningpolitiken inte är tillfredsställande. Liksom i fallet med den ekonomiska utmaning som covid-19 orsakade, var många centralbanker tvungna att genomföra okonventionella monetära planer. Denna avhandling syftar till att upptäcka effekten av kvantitativ lättnad (QE) och dess motståndare kvantitativ nedtrappning (QT) på bostadspriserna på den amerikanska fastighetsmarknaden. Som ett sätt att hantera detta problem utför denna forskning tidsvarierande rullande korrelationer som är korrelationer mellan två tidsserier på ett rullande fönster, fönstret för denna forskning kommer att vara månadsvis och föremål för historiska datapunkter från 280-månadersperioden i USA storstadspriserna bostäder och den federala balansräkningen mellan 1998 och 2022. Resultaten visar att det finns en positiv korrelation mellan de olika amerikanska bostadsmarknaderna och den amerikanska federala balansräkningen på majoriteten av de analyserade amerikanska marknaderna och finner en hög positiv korrelation mellan de olika regionala husprisindex och US National Home Price Index och slutligen förekomsten av spridningseffekter mellan städerna i städerna på hög nivå (t.ex. Los Angeles och Miami) och lågnivå (t.ex. Chicago och Atlanta), så att stigande trender i en stad speglas av följande förändringar i den andra staden i motsvarande nivå och vice versa.

Designs for deep ultraviolet (DUV) edge emitting laser diodes (LDs) based on the wurtzite III-nitride (III-N) material system are presented. A combination of proprietary and commercial advanced semiconductor LD simulation software is used to study the operation of III-N based DUV LDs theoretically. Critical factors limiting device performance are identified based on an extensive literature survey. A comprehensive design parameter space is investigated thoroughly with the help of advanced scripting capabilities. Several design strategies are proposed to eliminate the critical problems completely or partially. A DUV LD design is proposed based exclusively on AlInN active layers grown epitaxially on bulk AlN substrates because AlInN offers a promising alternative to AlGaN for the realization of LDs and LEDs operating in the DUV regime. The proposed AlInN-based design also features a tapered electron blocking layer (EBL) instead of a homogeneous one. Tapered EBLs redistribute the interfacial polarization charge volumetrically throughout the entire EBL thickness via compositional grading, and eliminate the parasitic inversion layer charge. AlGaN based DUV LD designs are explored also because at present, it may be difficult to grow AlInN epitaxially with superior crystalline quality. Polarization charge matching is proposed to improve electron and hole wavefunction overlap within the active region. Although the strategy of polarization charge matching has already been proposed in the literature to enhance performance of visible wavelength LEDs and LDs, the proposed design presents the first demonstration that polarization charge matching is also feasible for DUV LDs operating at sub-300 nm wavelengths. A lateral current injection (LCI) LD design is proposed featuring polarization-charge-matched barriers and regrown Ohmic contacts to avoid a group of issues related to the highly inefficient p-type doping of wide bandgap III-N materials in vertical injection designs. The proposed design partially decouples the problem of electrical injection from that of optical confinement. Although the idea of an LCI LD design has been proposed in the literature in the 90s to be used as longer wavelength active sources in optoelectronic integrated circuits using GaInAsP/InP and related material systems, the proposed design is the first theoretical demonstration that this concept can be applied to DUV LDs based on III-N material system. To solve the problem of hole transport in vertical injection designs, a DUV LD design based exclusively on AlGaN material system is presented, featuring an inverse-tapered p-waveguide layer instead of an EBL. Several EBL designs are investigated, and compared with conventionally-tapered EBL design. Through judicious volumetric redistribution of fixed negative polarization charge, inverse tapering may be exploited to achieve nearly flat valence band profiles free from barriers to hole injection into the active region, in contrast to conventional designs. Numerical simulations demonstrate that the inverse tapered strategy is a viable solution for efficient hole injection in vertical injection DUV LDs operating at shorter wavelengths (< 290 nm).