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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Det gäller att leva drogfritt sen, när livet drabbar oss : En kvalitativ studie av fyra kvinnor som lämnat ett beroende

Ivarjord, Emma January 2010 (has links)
I detta arbete har jag intervjuat fyra kvinnor vilka alla har varit beroende av alkohol eller droger. Mitt syfte har varit att fokusera på dessa missbrukskarriärers brytpunkter, det som lett till att kvinnorna lämnat sitt missbruk. Jag har studerat likheter och skillnader gällande vilka faktorer som varit betydelsefulla för dessa kvinnor under deras väg tillbaka till ett drogfritt och nyktert liv.Jag har i arbetet antagit en narrativ ansats, och kvinnorna och deras historier har getts mycket utrymme i min uppsats. Jag har använt mig av tematiska intervjuer då jag samlat in mitt arbetsmaterial. Jag har försökt att i möjligaste mån låta kvinnornas berättelser genomlysa mitt arbete, och jag hoppas jag gett dem rättvisa.De slutsatser jag kom fram till efter att ha bearbetat mitt insamlade material var att det aldrig var endast en enskild händelse som ledde till att de intervjuade kvinnorna beslutade sig för att lämna missbruket bakom sig. Beslutet föranleddes hos alla kvinnor av flera händelser som tillsammans gjorde att de valde att gå en annan väg.
242

The effect of process parameters on the properties of diamond-like carbon thin film

Chen, Jyun-Jia 28 July 2010 (has links)
Since the diamond like carbon features include high hardness and high wear resistance, low friction coefficient, chemical inertness, high resistance, low dielectric constant, the IR Transparency and field emission. The process of Diamond carbon film was usually by CVD or PVD techniques. However, high substrate temperature or low deposition rate and the can not make large area of films leads to limit the applications of diamond like film. Electrodeposition method is an innovative method to prepare DLC film and it meets these demands such as: equipment cheap, high deposition rate and larger area coatings. In this paper, ITO substrate was used for electrodeposition the diamond-like carbon films and to evaluate the possibility for the large area of DLC films.For the process of electrical deposition, the electrolyte consists of acetic acid and DI water mixed in different proportions. The deposition process were conditioned as: electrolyte concentration between 0.01% and 0.8%; voltage from 2.1V to 50V; growth temperature in the range of 300C ~ 850C. In addition, by using the control variables method, the deposition parameters including voltage, deposition temperature and solution concentration of electrolyte were varied to evaluate the characteristics and quality of diamond-like carbon films. The n & k film analyzer (n & k Analyze), X ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) were used to characterize the surface morphology, microstructure and compositional analysis. The reflectivity, transmittance, and refractive index of DLC Films were revealed by the n & k analyzer. Hence, the best conditions used for anti-reflective layer and projections Eopg can be achieved. For SEM analysis, the DLC film with uniformity surface structure can be found. Additionally, the current - time graph can be used to predict the properties of film varied with the applied voltage, percent of concentrations, growth temperature etc.. The microstructure of DLC film was investigated by the XPS measurement; the sp2 / sp3 ratio varies from the growth parameters changes. The hydrogen content of DLC films was obtained by FTIR measurements, the contents decrease as the operating voltage, electrolyte concentration and the substrate temperature increase. As for the DLC deposited on ITO glass as an anti-reflective layer, the experimental results showed that DLC film can reduce the reflectivity from 40% to 70%. Finally, the results obtained show a reasonable match for various measurements. T he characteristics of DLC films also shows that it very depends on the deposited parameters and the relationship beteen them was discussed in detailed. Some of the advance study will be investigated in future.
243

Study of Broad-band Quantum Structure Grown by Molecular Beam Epitaxy

Chen, Chun-Yang 28 July 2010 (has links)
The thesis focuses on the study of asymmetric multiple quantum wells(AMQWs) grown by molecular beam epitaxy (MBE) in the Riber Compact 21T MBE system. We investigate AMQW structures in which the well width is varied but the material compositions of the wells and the barriers are kept constant. Also, we have investigated AMQWs with p-type modulation doping at the barrier region and the AMQWs of different well widths without changing the well compositions. The AMQW samples are obtained the emission spectra by using photoluminescence (PL), electroluminescence (EL), photo-current and photoreflectance (PR) in the experiments. Also, The AMQW samples (AMQ100-70-40 and AMQ-100-MD70-40) are fabricated into laser diodes to obtain the characteristics of device in this study. The threshold current density Jth of laser diode is measured about 2 kA/cm2.The internal quantum efficiency £bi and the absorption £\ of AMQ-100-70-40 are 34.7% and 9.47 cm-1 respectively. The internal quantum efficiency £bi and the absorption £\ of AMQ-100-MD70-40 are 22.2% and 10.56 cm-1 respectively. Moreover, we present the InGaAsP AMQW samples grown by MOCVD to compare with the InGaAs/InAlGaAs AMQW samples. The broad-band property is valuable for application of optical communication. It is highly desirable to have broadly tunable lasers and broad-band semiconductor optical amplifiers (SOAs) in the 1.3 or 1.55£gm to handle more number of channels increasing the volume of information traffic for future optical communication networks. The band-band light source is also desirable in medical science for the optical coherence tomography (OCT).
244

Antenna Gain Enhancement with More Subwavelength Holes and Dual-Band Design with Coplanar Structure of Metamaterial Radomes

Chen, Kai-shyung 28 July 2010 (has links)
In the thesis, we designed a metamaterial radome to increase the antenna gain. Owing to the need of high-directivity radiation in fix-point communications, antenna array and reflective antenna had been used to increase the directivity of antenna traditionally. Complicated feed and huge antenna size are the disadvantages of these techniques. We proposed a simpler metamaterial radome to increase the antenna gain. We find the subwavelength-hole structure formed by four Jerusalem cross structures can collimate electromagnetic wave originally spreading out from the holes. With the same size, multiple subwavelength holes in metamaterial radome can further enhance the antenna gain. We showed that metamaterial radome with 9 subwavelength holes can improve the gain by about 3.5 dB. In addition, we applied the concept of Fabry-Perot Cavity (FPC) to find the suitable distance between the radome and the antenna. When the resulting electromagnetic waves are in-phase, the radome can increase the antenna gain effectively. Recently, high-directivity radiation in fix-point communications is required and in the meantime multi-mode communication systems have become more and more popular. For practical purposes, we designed a coplanar dual-band metamaterial radome to be operated at 2.5 GHz and 3.5 GHz for WiMAX. This structure allows adjustment of its characteristics independently at each band. This coplanar dual-band radome can enhance the antenna gain by about 1.74 dB and 2.08 dB at 2.5 GHz and 3.5 GHz, respectively.
245

Photonic Ultra-wide Band Monocycle Generation through Electro Absorption Modulator with Single Wavelength Light

Chen, Po-Yen 06 September 2010 (has links)
Ultra Wide Band (UWB) is a short-pulse electrical signal which is widely used for short distant wireless communication because its low path loss, good immunity to multipath propagation, and high data rate. The reason of using optical fiber as carrier is fiber can bust up the communication capacitance in long distance range because of high capacitance, low loss propagation. Thereby, the technique of UWB signal on fiber has become more and more important. In this work, a novel method using electro-absorption modulation with short termination for interface of optical fiber and generate UWB signal is proposed and demonstrated. The structure is simple.This method don¡¦t need employing any complicated frequency mixer, or complex systems. This work need to generate optical pulse with high energy, which is feded into the EAM. The signal can generate electrical pulse and build electrical field on EAM in the same time. The optical pulse is modulated by the electrical field on EAM. Using this way, we can generate UWB optical signal.
246

The tensile properties of sub-micron Al

Hung, Pei-Ching 29 June 2004 (has links)
In this experimental, we use ECAE with route BC to produce the ultrafine-grain Al and use different annealing temperature to get grain size at 0.4
247

Feasibility Study of Phononic Crystal Structure Applied as Underwater Absorptive Material.

Lin, Yi-Hsien 16 August 2005 (has links)
¡§Phononic crystal,¡¨ a binary-composite medium composed of a square array of parallel circular brass cylinders in a water matrix is reported. Phononic crystal exists total band-gaps phenomenon which is caused by destructive interference of Bragg reflection in their acoustic transmission spectrum. This Bragg reflection theorem is also a basis for searching the total band-gaps in this thesis. Because of the band-gaps of the phononic crystal, it is very appropriate for applying phononic crystal in underwater absorptive materials. This research presents the Bragg theorem prediction of brass/water acoustic forbidden bands structure with three kinds of different filling fractions, 5 %, 10 %, and 20 %, and three kinds of transducers. Their central frequency are 300 kHz, 500 kHz, and 1 MHz, respectively, and their bandwidths are 210 kHz~390 kHz, 350 kHz~650 kHz, and 700 kHz~1300 kHz, respectively. Furthermore, in order to find total band-gaps, [100] and [110] directions are measured in this research. The band-gaps of phononic crystal in this research are designed by the couple probes of lowest frequencies 300 kHz in our laboratory. Although the devices of underwater acoustics usually operate in 15~200 kHz, it is also proved indirectly that to design and to apply phononic crystal in underwater absorptive materials are workable. In addition, the measurement results of band-gaps of single frequency are the same as broad-band frequencies using ultrasonic analyzer in this thesis. Therefore, it is a good way to survey the band-gaps with broad-band frequencies method first, and then to use single frequency method measuring deeply drop of the band-gaps. This research uses Bragg reflection theorem, to calculate approximate position of band-gaps, and predicts n=1~3 total band-gaps successfully in experiments. It is also proved that using this kind of underwater absorptive materials of phononic crystal has the effect of camouflaging submarine purpose with specific frequencies. This is an easiest theorem to survey band-gaps of phononic crystal, and must be a most useful tool to design all kinds of absorptive materials of phononic crystal.
248

Generalized Maximum Likelihood Algorithm for TOA Estimation in Multi-band OFDM UWB Systems

Yang, Shih-Wei 26 August 2005 (has links)
The fine time resolution of ultra wide-band (UWB) systems enables applications in TOA/TDOA based high precision wireless indoor location. The main purpose of this thesis is to investigate TOA estimation in multi-band OFDM UWB systems. We propose an effective and simplified TOA estimation algorithm for multi-band OFDM standard. The proposed algorithm is based on the generalized maximum-likelihood (GML) algorithm. The TOA estimation algorithm utilizes the preamble signal in multi-band OFDM system. We modify the realization method of GML algorithm according to the preamble signal properties and apply it to multi-band OFDM system. From simulation results, by comparing with cross correlation algorithm and the original GML algorithm, the proposed algorithm has ability to mitigate multipath interference and improves TOA estimation accuracy. In this thesis we also discuss the thresholds setting and SNR estimation problems to make the proposed algorithm more realizable.
249

The Study and Fabrication of Ultra-Wideband Optical Amplifier Based on Cr4+:YAG Crystal Fiber

Chen, Shao-syuan 04 July 2007 (has links)
The maximum capacity of an optical fiber transmission system more than doubled every year to match the fast-growing communication need. The technology break through in dry fiber fabrication opens the possibility for fiber bandwidth all the way from 1300nm to 1600nm. The fast increasing demand of communication capacity results in the emergence of wavelength division multiplexing (WDM) technology, which results in the need for ultra-wideband optical amplifier. Cr4+:YAG has a strong spontaneous emission that covers 1300nm to 1600nm. Besides, its absorption spectrum is between 900nm to 1200nm, which matches with the pumping source in current erbium doped optical amplifier. Such a fiber is, therefore, eminently suitable for optical amplifier applications. In this article, we will introduce the development of ultra-wideband optical amplifier using the double-clad Cr4+:YAG crystal fiber, which is grown by laser heated pedestal growth(LHPG) technique. Its material properties as well as optical gain will be characterized. By butt-coupling method, a low insertion loss of 4.2 dB was achieved in a SMF-CDF-SMF configuration, and it was measured to demonstrate a gross gain of 2.4 dB at 1 W bi-directional pump power. Moreover, theoretical models and numerical simulations have been developed to predict the experimental results. Numerical simulation indicates that the efficiency of mode overlapping between signal and pump is crucial to gain performance. The mode overlapping efficiency is about 25%~30% for our crystal fiber under current circumstances. In the future, we will make an attempt to reduce the index contrast between core and cladding for better mode overlapping efficiency. At the same time, we also try to grow crystal fiber of smaller core diameter to improve gain performance.
250

A Study of Gain-flattened L-Band EDFA

Tseng, Wen-Hung 27 June 2000 (has links)
ABSTRACT In this thesis, we investigate the amplification characteristics of gain-flattened L-band (1570-1600 nm) erbium-doped fiber amplifier (EDFA) by employing the 1480 nm bi-directional pumping configuration. L-Band EDFAs are attractive because the use of L-band and C-band (1530-1560 nm) EDFAs in parallel greatly expands the amplification wavelength region. We adjusted the length of erbium-doped fiber (EDF) to achieve the flat amplification characteristics in the 1573-1600 nm wavelength region without using gain equalizers. The L-band EDFA exhibited a signal gain of 23 dB with good uniformity (less than 1 dB) and a noise figure of 6.9 dB for a 1580 nm signal of 16-channel WDM system. We also used the simulation tools to investigate the characteristics of L-band EDFA with the same configuration. The simulation results quite agree with the experimental data.

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