• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 14
  • 6
  • 5
  • 3
  • 2
  • Tagged with
  • 41
  • 41
  • 11
  • 6
  • 6
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 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.
11

Design and Fabrication of Wafer Level Dual-Mode Thin Film Bulk Acoustic Filters

Li, Jia-Ming 09 August 2011 (has links)
This study describes the design and fabrication of dual-mode film bulk acoustic resonator (TFBAR) devices to construct wafer level T-ladder type filters. Reactive radio-frequency (RF) magnetron sputtering method was used to deposit c-axis- tilted ZnO piezoelectric thin films. The piezoelectric ZnO thin films were deposited by a two-step method at room temperature with off-axis. In this investigation, off-axis distance was varied to determine the optimal growth parameters of the tilted piezoelectric thin film. The SEM and XRD analysis reveal that ZnO thin films deposited at off-axis distances of 35 mm yielded a highly textured and sufficiently-tilted ZnO piezoelectric layer for dual-mode TFBAR. Additionally, the ZnO piezoelectric layer with off-axis distances of 35 mm exhibited enhanced competitive growth, and had a c-axis-tilted angle of 5¢X. To explore the relationship between the c-axis-tilted angle and the dual-mode resonance frequency responses (fL and fS) of TFBAR, two TFBAR devices were fabricated with ZnO c-axis tilted at 4.4¢X and 5¢X, respectively. The TFBAR device with 5¢X-tilted ZnO layer exists shear and longitudinal resonant modes. The center-frequency of longitudinal resonant mode is 2.2 times that of the shear resonant mode. The longitudinal mode is suitable for designing as a communication receiver (Rx) device at WCDMA band. On the other hand, the shear mode of TFBAR is suitable for EGSM-900 band. To optimize the characteristics, the filter was annealed by CTA treatment in 400 ¢J. For the frequency responses of the longitudinal wave, the insertion loss was upgraded from -5.77 dB without annealing to -4.85 dB as annealed, the band rejection was reduced from 13.57 dB to 12.65 dB, the bandwidth was broaden from 69.69 MHz to 73.12 MHz. On the other hand, for the frequency responses of the shear wave, the insertion loss was upgraded from -9.94 dB to -8.21 dB, the band rejection was reduced from 13.74 dB to 13 dB, the bandwidth was decreased from 28.13 MHz to 28.12 MHz.
12

A Dual-Mode Message Delivery System with Time Constrained Paging Mechanism

Cheng, Hsu-Ching 11 September 2012 (has links)
In the thesis, we propose a dual-mode message delivery system with mechanisms of time constrained paging and multi-class message. The pairing decision depends on the effective pairing time defined by the system when a bluetooth device comes into service range. Within the constrained pairing time, central server can deliver a message to the bluetooth device directly without re-pairing. Otherwise, the bluetooth device has to be paired with an intermediate node before it can receive a message. In addition, we store the number of times that bluetooth devices can move into the service range into a data base in order to send multi-class messages to these bluetooth devices. To demonstrate the proposed schemes, we implement a central server on Linux system and intermediate nodes on Window Mobile platform. We also design control packets associated with their message formats. Control messages can be exchanged between the central server and the intermediate node by the control packets, and data messages can be transmitted in a heterogeneous network, consisting of bluetooth and Wi-Fi. Finally, we measured the time saved without using pairing procedure and also verified that the system can dynamically adjust the classes of messages according to the number of times that bluetooth devices enter to the service range.
13

The Impact of Continuous and Discontinuous Cycle Exercise on Affect: An Examination of the Dual-Mode Model

Greeley, Sam 01 January 2012 (has links)
Low-volume, high-intensity interval training has been garnering attention in the exercise physiology literature recently due to its proposed time-efficiency. Also, recent work comparing continuous exercise to high-intensity interval training demonstrated superior ratings of perceived enjoyment following interval training. However, the dual-mode model suggests that exercise above ventilatory threshold (VT) done continuously will result in an almost homogenous decline in affect, which may reduce adherence. Numerous studies confirm the dual-mode model's prediction of reduced affect when exercising above VT, but no research to date has applied the model's predictions to interval training. The purpose of this study was to examine the dual-mode model using interval training. Based on the model, interval exercise above VT should produce a homogenous and significant decline in affect during exercise. Ten participants (mean age = 21.6 ± 2.4 yrs) completed the study. Participants were screened by a physician's assistant on their first visit to ensure they were low-risk and had no symptoms (cardiovascular, pulmonary, metabolic, or orthopedic) that would preclude safe participation in an exercise training program. Participants performed a maximal exercise test during their second visit to the lab. The final four visits were exercise trials 20 minutes in duration: 1) continuous at 20% below VT [Continuous-Moderate], 2) continuous at VT [Continuous-Heavy, 3) 10 x 60-second intervals at VT [Interval-Heavy], 4) 10 x 60-second intervals at 20% above VT [Interval-Severe]. Results indicated that enjoyment and affect was significantly greater during Continuous-Moderate and Interval-Heavy compared with Continuous-Heavy. Interval-Severe approached inducing significantly greater enjoyment and affect compared with Continuous-Heavy, however the study was likely underpowered to achieve significance. The findings of this study suggest that utilizing interval training may help preserve affect, even when performing exercise above VT.
14

OPTIMIZATION OF A DUAL-MODE SURFACE PLASMON RESONANCE SENSOR

Bathae Kumaresh, Prasanth 01 January 2007 (has links)
Surface plasmon waves are TM polarized charge density waves that propagate at the interface of two media with real dielectric constants of opposite sign (i.e. liquid dielectric and certain metals). Surface plasmon resonance (SPR) sensors use these waves to detect refractive index changes adjacent to the metal layer. Refractive index changes arise from the binding of an analyte (e.g. a target molecule, protein, or bacterium) to the functionalized metal layer or from interfering effects such as changes in solution index. Standard, single channel SPR sensors cannot differentiate these two effects as their design allows only one mode to be coupled. This novel self-referencing technique employs two surface plasmon modes to simultaneously measure surface binding and solution refractive index. Dual surface plasmon modes are achieved by matching the refractive indices on either side of the metal film. The two modes generated - symmetric, long-range surface plasmon (LRSP) and anti-symmetric, short-range surface plasmon (SRSP) - have different field profiles and hence assist in differentiating solution refractive index changes from surface layer formation. Amorphous Teflon, with a refractive index close to water, is chosen as the buffer layer and gold is chosen as the metal layer. Magnesium fluoride, with a higher index than Teflon, is used as the buffer layer when using ethanol as the base solution. The sensor operation was optimized through simulations to yield higher sensitivity, lower reflectivity and resonances within the spectrometers range. Optimization results showed good performance over a wide range for Teflon, MgF2 and gold thicknesses which helped in the fabrication of the sensor. Demonstration of self-referencing operation was done through two different sets of experiments: (1) formation of an alkanethiol self-assembled monolayer on gold in the presence of ethanol and methanol solutions having different refractive indices and (2) streptavidin-biotin binding with solutions of different NaCl concentration and thus different refractive indices. In both these experiments, the resonance wavelengths were accurately predicted, reflectivity varied by 10-15% and sensitivity by 25% from that of the simulated values.
15

Mark II Dual-Mode Vehicle Design and Analysis

Maheshwary, Anurag, Matson, Edward Franklin, Woods, David DeForest 10 July 1998 (has links)
In the Spring of 1998, the Virtual Corporation at Virginia Tech demonstrated the ability of Linear Switched Reluctance Propulsion (LSRP) to propel a vehicle on a track using only the interaction of a passive magnetic component carried on the vehicle with electromagnets built into the track. The Mark II project was a follow-on effort to complete a thorough design analysis of a second iteration vehicle which features the complete functionality of the original vehicle, with the addition of the ability to enter and exit the LSRP track system using remote control and an electric motor. The new vehicle also features certain design improvements in communications and structural rigidity. This paper elaborates on the process of design and analysis of the vehicle and ramp systems, including detail design drawings, finite element analysis of the vehicle chassis, powertrain subsystem analysis, and detailed analysis of the ramp surface contour design. / Master of Engineering
16

Design and Analysis of a Dual-Mode Cascaded-Loop Frequency Synthesizer

Lai, Xiongliang 09 July 2009 (has links) (PDF)
A new architecture for a frequency synthesizer with adjustable output frequency range and channel spacing is introduced. It is intended for the generation of closely spaced frequency channels in the GHz range while producing minimal spurious phase noise components. The architecture employs two independent phase-locked loops that are driven in cascade by a single reference oscillator. The approach provides fine resolution and wide bandwidth as well as low phase noise and should find application in many contemporary communication systems. The synthesizer can be operated in either of two different modes: nonfractional and mini-denominator fractional modes. The architecture produces no fractional spurs in the first mode and relatively small phase spurs when operated in the second mode. For example, in an application to a P-GSM 900 system, it is capable of tuning from 890 – 915 MHz with a channel spacing of 200 kHz and shows worst case phase spurs of -100 dBc at an offset frequency of 833 kHz. Because of the low magnitude and location of the worst case spurs, the phase-locked loop filters can be designed with a wide bandwidth which in turn results in a fast settling time. A linear frequency-switching settling time (to 0.01% of frequency increments) of 128 μs is typical in the P-GSM 900 application.
17

High Efficiency Single-stage Grid-tied PV Inverter for Renewable Energy System

Zhao, Zheng 21 May 2012 (has links)
A single-phase grid connected transformerless photovoltaic (PV) inverter for residential application is presented. The inverter is derived from a boost cascaded with buck converter along with a line frequency unfolding circuit. Due to its novel operating modes, high efficiency can be achieved because there is only one switch operating at high frequency at a time, and the converter allows the use of power MOSFET and ultra-fast reverse recovery diode. This dissertation begins with theoretical analysis and modeling of this boost-buck converter based inverter. And the model indicates small boost inductance will leads to increase the resonant pole frequency and decrease the peak of Q, which help the system be controlled easier and more stable. Thus, interleaved multiple phases structure is proposed to have small equivalent inductance, meanwhile the ripple can be decreased, and the inductor size can be reduced as well. A two-phase interleaved inverter is then designed accordingly. The double-carrier modulation method is proposed based on the inverter's operation mode. The duty cycle for buck switch is always one if the inverter is running in boost mode. And the duty cycle for boost switches are always zero if the inverter is running in buck mode. Because of this, the carrier for boost mode is stacked on the top of the carrier for buck mode, as a result, there is no need to compare the input and output voltage to decide which mode the inverter should operate in. And the inverter operates smoothly between these two modes. Based on similar concept, three advanced modulation methods are proposed. One of them can help further improve the efficiency, and one of them can help increase the bandwidth and gain, and the last one takes the advantage of both. Based on similar concept, another three dual-mode double-carrier based SPWM inverters are proposed. With both step-up and step-down functions, this type of inverter can achieve high efficiency in a wide range because only one switch operates at the PWM frequency at a time. Finally, the simulation and experiment results are shown to verify the concept and the tested CEC (California Energy Commission) efficiency is 97.4%. It performs up to 2% more efficiently better than the conventional solution. / Ph. D.
18

Iudicet iudicarive iubeat: reflexões sobre as origens do processo civil romano e da bipartição / Iudicet iudicarive iubeat: remarks on the origins of the Roman civil procedure and its dual mode.

Böttcher, Carlos Alexandre 12 September 2012 (has links)
Iudicet iudicarive iubeat. Reflexões sobre os origens do processo civil romano e as causas da bipartição. Depois da introdução, o segundo capítulo analisa os aspectos da história constitucional da Monarquia e início da República, sobretudo as críticas à historiografia tradicional no tocante à passagem de um regime ao outro, além de estudar a religião romana arcaica. O terceiro capítulo busca elementos da administração da justiça no direito comparado (babilônico, gregos e germânicos), enquanto que o quarto analisa o início do processo criminal romano. O quinto capítulo, por sua vez, investiga as várias teorias acerca do início do processo civil, como da arbitragem, defesa privada, Volksjustiz etc. O sexto capítulo trata das várias teorias da bipartição, procurando estabelecer se teve caráter originário no processo civil romano e suas causas. O sétimo capítulo analisa as legis actiones mais antigas (legis actio sacramento, legis actio per manus iniectionem e legis actio per iudicis arbitrive postulationem). O oitavo capítulo tenta verificar o conteúdo da iurisdictio romana e suas relações com o imperium, enquanto que o capítulo nono trata das figuras do iudex e do arbiter. O décimo capítulo apresenta as críticas às teorias expostas, formulando hipótese acerca do surgimento do processo civil romano por meio de resolução das controvérsias no âmbito da comunidade anteriormente à formação da civitas com base em cultura e religião comuns, razão por que a presente tese propõe a adoção do termo justiça comunitária pré-cívica para qualificar esse sistema, propugnando pelo abandono das expressões autotutela/justiça privada e Volksjustiz por serem ambas portadoras de equívocos. No tocante à bipartição, a presente tese considera verossímil sua consolidação na época da Lei das XII Tábuas em razão sobretudo do fenômeno da dessacralização do processo / Iudicet iudicarive iubeat. Remarks on the origins of the Roman civil procedure and the causes of its dual mode. After the introduction, the second chapter analyses some aspects of constitucional history of Monarchy and the beginning of Republic, mainly the critics against the tradicional historiography concerning the transition from the first to the latter and it also studies the ancient Roman religion. The third chapter seeks elements from the administration of justice in comparative law (Babylonic, Greeks and Germanics), while the forth one analyses the beginning of the criminal persecution in Rome. The fifth chapter investigates the theories about the beginning of civil litigation, such as arbitration, self help, Volksjustiz etc. The sixth chapter deals with the dual mode procedure theories, trying to set if is had an original character and its causes. The seventh chapter analyses the most ancient legis actiones (legis actio sacramento, legis actio per manus iniectionem e legis actio per iudicis arbitrive postulationem). The eighth chapter tries to verify the content of the Roman iurisdictio and its relationships with imperium, while the nineth chapter deals with the figures of iudex and arbiter. The last chapter presents the critics to the analysed theories and formulates a hypothesis about the beginning ot the Roman civil procedure through the disputes settlement inside the community before the creation of civitas basing on common culture and religion. Thus, the thesis proposes the adoption of the term justiça comunitária pré-cívica (precivic community justice) in order to qualify this system, refusing the expressions self help, private justice and Volksjustiz, who are dubious. Regarding the dual mode, the thesis sustains it is plausible that it had already benn consolidated by the time of the Twelve Tables Law according mainly to the dessacralization of process.
19

A Performance Analysis of a Rocket Based Combined Cycle (RBCC) Propulsion System for Single-Stage-To-Orbit Vehicle Applications

Williams, Nehemiah Joel 01 December 2010 (has links)
Rocket-Based Combined Cycle (RBCC) engines combine the best performance characteristics of air-breathing systems such as ramjets and scramjets with rockets with the goal of increasing payload/structure and propellant performance and thus making LEO more readily accessible. The idea of using RBCC engines for Single-Stage-To-Orbit (SSTO) trans-atmospheric acceleration is not new, but has been known for decades. Unfortunately, the availability of detailed models of RBCC engines is scarce. This thesis addresses the issue through the construction of an analytical performance model of an ejector rocket in a dual combustion propulsion system (ERIDANUS) RBCC engine. This performance model along with an atmospheric model, created using MATLAB was designed to be a preliminary `proof-of-concept' which provides details on the performance and behavior of an RBCC engine in the context of use during trans-atmospheric acceleration, and also to investigate the possibility of improving propellant performance above that of conventional rocket powered systems. ERIDANUS behaves as a thrust augmented rocket in low speed flight, as a ramjet in supersonic flight, a scramjet in hypersonic flight, and as a pure rocket near orbital speeds and altitudes. A simulation of the ERIDANUS RBCC engine's flight through the atmosphere in the presence of changing atmospheric conditions was performed. The performance code solves one-dimensional compressible flow equations while using the stream thrust control volume method at each station component (e.g. diffuser, burner, and nozzle) in all modes of operation to analyze the performance of the ERIDANUS RBCC engine. Plots of the performance metrics of interest including specific impulse, specific thrust, thrust specific fuel consumption, and overall efficiency were produced. These plots are used as a gage to measure the behavior of the ERIDANUS propulsion system as it accelerates towards LEO. A mission averaged specific impulse of 1080 seconds was calculated from the ERIDANUS code, reducing the required propellant mass to 65% of the gross lift off weight (GLOW), thus increasing the mass available for the payload and structure to 35% of the GLOW. Validation of the ERIDANUS RBCC concept was performed by comparing it with other known RBCC propulsion models. Good correlation exists between the ERIDANUS model and the other models. This indicates that the ERIDANUS RBCC is a viable candidate propulsion system for a one-stage trans-atmospheric accelerator.
20

Novel Quadruple-mode, Dual-mode and Dual-band Dielectric Resonator Filters and Multiplexers

Memarian, Mohammad January 2009 (has links)
Dielectric resonators offer high-Q (low loss) characteristics which make them ideal for filters with narrow bandwidth and low insertion loss specifications. They are mainly used in satellite and wireless system applications. Such applications desire the highest performance filters with the lowest amount of size and mass, which has been the main motivation for size reduction techniques invented over the past three decades for these filters. In addition with the emergence of different communication system technologies, several bands are now required to be supported by a single front-end, calling for emergence and development of dual-band and multi-band filters. To date few work has been done in the area of dual-band dielectric resonator filters. Dielectric resonators filters are important components in many communication systems, when a group of such filters are brought together to perform multiplexing of RF channels. These multiplexer systems tend to be fairly complex and bulky in design, and there is strong desire to reduce their size and mass to the maximum extent possible. Novel quadruple-mode, dual-mode, and dual-band filters as well multiplexers are presented in this thesis. The first ever quadruple-mode dielectric resonator filter using the simple cylinder structure is reported in this work. A cylindrical dielectric resonator sized appropriately in terms of its diameter and height is shown to operate as a quadruple-mode resonator, which is achieved by having two mode pairs of the structure resonate at the same frequency. Single-cavity, quad-mode filters and higher order 4n-pole filters are realizable using this quad-mode cylindrical resonator, offering significant size reduction for dielectric resonator filter applications. The structure of the quad-mode cylinder is then simplified by cutting lengthwise along the central axis of the cylinder, to produce a half-cut cylinder suitable for operation in a dual-mode regime. Novel dual-mode, 2n-pole filters are realizable using this half-cut cylinder, by making the two resonances equal in frequency. The dual-mode half-cut filter is shown to be a strong contender for replacing existing dual-mode filters used in satellite and wireless applications, as it offers superior size and mass characteristics. By making the resonances unequal in frequency, novel dual-band filters and multiplexers are further realizable, by carrying separate frequency bands on different resonant modes of the structure. The first true orthogonal mode dual-band dielectric resonator is presented in this work, using the half-cut structure. Multiplexers are also derived from these dual-band resonators, which greatly reduce size and mass of many-channel multiplexers at the system level, as each two channels are overloaded in one physical branch. Full control of center frequencies of resonances, input and inter-resonator couplings are achievable, allowing realization of microwave filters with different bandwidth, frequency, and return loss specifications, as well as advanced filtering functions with prescribed transmission zeros. Spurious performance of the half-cut cylinder can also be improved by cutting one or more through-way slots between opposite surfaces of the resonator. Size and mass reduction achieved by using the full and half-cut resonators described in this thesis, provide various levels of size reduction in microwave systems, both device and system level.

Page generated in 0.0408 seconds