• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 314
  • 62
  • 51
  • 48
  • 24
  • 19
  • 12
  • 11
  • 10
  • 5
  • 5
  • 5
  • 4
  • 4
  • 2
  • Tagged with
  • 780
  • 62
  • 57
  • 51
  • 51
  • 47
  • 46
  • 41
  • 40
  • 37
  • 36
  • 35
  • 30
  • 30
  • 30
  • 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.
141

Noise Suppression and Isolation in Mixed-Signal Systems Using Alternating Impedance Electromagnetic Bandgap (AI-EBG) Structure

Choi, Jinwoo 08 December 2005 (has links)
With the evolution of technologies, mixed-signal system integration is becoming necessary for combining heterogeneous functions such as high-speed processors, radio frequency (RF) circuits, memory, microelectromechanical systems (MEMS), sensors, and optoelectronic devices. This kind of integration is required for convergent microsystems that support communication and computing capabilities in a tightly integrated module. A major bottleneck with such heterogeneous integration is the noise coupling between the dissimilar blocks constituting the system. The noise generated by the high-speed digital circuits can couple through the power distribution network (PDN) and this noise can transfer to sensitive RF circuits, completely destroying the functionality of noise-sensitive RF circuits. One common method used for mixed-signal integration in the package is splitting the power and/or ground planes. The gap in the power and ground planes can partially block the propagation of electromagnetic waves. However, electromagnetic energy can still couple through the split, especially at frequencies greater than 1 GHz. The AI-EBG structure in this dissertation has been developed to suppress unwanted noise coupling in mixed-signal systems and this AI- EBG structure shows excellent isolation (-80 dB ~ -140 dB), which results in a noise coupling-free environment in mixed-signal systems. The AI-EBG structure would be part of the power distribution network (PDN) in systems and is expected to have a significant impact on noise suppression and isolation in mixed-signal systems in future.
142

Multi-Sensor Noise Suppression and Bandwidth Extension for Enhancement of Speech

Hu, Rongqiang 17 January 2006 (has links)
Speech enhancement has been an active research problem for decades and continues to be an important problem. This is made even more true by the proliferation of portable devices having audio input capabilities. In the presence of noise, both the quality and intelligibility of speech signals have been significantly deteriorated. The proposed research are the frameworks for improving the quality/intelligibility of the degraded speech: 1) a single-channel noise suppression system based on perceptual speech detection 2) multi-sensor noise suppression system for acoustic harsh environments based on non-air conductive sensors 3) a speech bandwidth extension system for telephone speech Significant improvement in both speech intelligibility and quality from the proposed frameworks are indicated from extensive experiments, inlcuding MOS, DRT, speech recognition task, and log spectral distortion.
143

Novel rf mems tunable filters with adjustable spurious suppression

Sekar, Vikram 15 May 2009 (has links)
This thesis presents the theory and design of fixed and Radio Frequency (RF) Microelectromechanical Systems (MEMS) -based tunable microwave filters for RF and microwave applications. The methodology for the design of coupled resonator filters is explained in detail and is used to design an end-coupled microstrip filter at 1.5 GHz with inductive loading using a stepped microstrip discontinuity to lower the resonance frequency of the half-wavelength microstrip resonator. The fabricated endcoupled filter shows center frequencies of 1.36 GHz and 1.03 GHz in the unloaded and loaded state respectively, with insertion losses between 1.2-1.5 dB and return loss better than 10 dB in both states. The filter response shows spurious passbands at approximately twice the filter center frequencies. To overcome this problem and improve the upper rejection skirt of the filter, microstrip resonators with tapped input/output coupling and mixed inter-resonator coupling are used to suppress the spurious passband by introducing a transmission zero at spurious resonance frequency. Measurement results for the fabricated tapped-resonator filters show an improvement of the upper rejection skirt due to spurious suppression to a level of -40 dB, with insertion loss of 1.2-1.5 dB for the same center frequencies. The concepts developed from fabrication and measurement of fixed-tuned microstrip filters are used to design an inductively-loaded RF MEMS tunable filter with adjustable spurious suppression implemented using packaged metal-contact switches. The two-pole 5% filter has a tuning range of 17% from 1.06 GHz to 1.23 GHz with an insertion loss of 1.56-2.28 dB and return loss better than 13 dB over the tuning range. The inductive loading mechanism is used to tune the open-ended quarter wavelength stub such that a tunable transmission zero supresses the spurious resonance as the filter center frequency is tuned. The spurious passband response in both states is suppressed below -20 dB. The unloaded quality factor (Q) of the filter varies from 127 to 75 as the filter is tuned. The equivalent circuit model for the series metalcontact packaged RF MEMS switch used in the tunable filter is derived from full-wave electromagnetic simulations and used to predict the effect of MEMS switch parasitics on the overall performance of the tunable filter.
144

Study of Noise Suppression and Circuit Design of a Dual Phase-Locked Loop System

Tsai, Wen-shiou 23 July 2009 (has links)
This thesis is composed of three parts. In the first part, analysis and discussion of phase noise in phase-locked loop is made. Because OFDM upconverter requires high phase noise performance, we therefore study the mechanism of noise suppression in a proposed dual phase-locked loop, and then derive the formula to predict the circuit characteristics. In the second part, experiment and simulation of a dual phase-locked loop is performed for comparison. The experiment uses hybrid circuit combined with related equipment and components to measure the noise suppression characteristics in a dual phase-locked loop. The simulation relies on the component behavioral model in ADS. Comparison between simulation and measurement shows good agreement. In the third part, this thesis carries out a 1.55¡V2.3 GHz frequency synthesizer RFIC design for DVB up-down architecture using TSMC 0.18£gm CMOS process. The test results validate the chip design.
145

Cognitive depletion in emotion regulation: age differences depend on regulation strategy

Senesac, Erin 25 June 2010 (has links)
Recent work has suggested that emotion regulation of inner emotional experience requires fewer cognitive resources for older adults than for young adults (Scheibe&Blanchard-Fields, 2009). The present study investigated whether cognitive costs are reduced for various types of emotion regulation strategies or only for certain types. The suppression of emotional expression, for example, is a particularly costly strategy for young adults, but little information exists regarding its cognitive costs for older adults. Furthermore, suppression of emotional expression is not a strategy that older adults are likely to use or that they become more effective at using. By contrast, the regulation of inner emotional experience has been shown to be more effective in older adults and presents less of a cognitive cost. The present study examined the cognitive costs of regulation of inner emotional experience (to conceptually replicate previous findings) and the cognitive costs of suppression of the outer expression of emotion. The results suggest that regulating and suppressing emotions do not require the same degree of resources for older and young adults. Whereas older adults may require more resources to suppress expression of emotions than to regulate emotions, young adults appear to require more resources to regulate emotions than to suppress the expression of emotions.
146

The influence of pre-existing memories on retrieval-induced forgetting

Goodmon, Leilani B 01 June 2005 (has links)
When people form episodic connections between memories that share a common retrieval cue, the tendency for those memories to interfere in later retrieval is often eliminated, and forgetting of the interfering information is reduced. For example, episodic integration protects memories from retrieval-induced forgetting (RIF), a phenomenon in which practicing retrieving some associates of a cue leads to the suppression of others that interfere with retrieval (Anderson, Green, and McCulloch, 2000). The purpose of this study was to determine whether semantic integration, as a result of pre-existing associations between practiced items and their unpracticed competitors, also moderates RIF. This research was motivated by the existence of many pre-existing associations between the practiced and unpracticed sets in one study that failed to replicate the RIF effect with item specific cues (Butler, William, Zacks, and Maki, 2001). It was hypothesized that pre-existing associations increase the implicit, semantic integration among the items, insulating them from inhibitory effects. The results were consistent with this hypothesis: when associations between the practiced and non-practiced sets were maximized, no forgetting was observed, however when such associations were minimized, there were reliable levels of RIF. The benefits of semantic integration were replicated across four experiments including one that used Butlers original materials and design. Furthermore, when Butlers items were simply re-arranged in order to minimize the associations and thus reduce semantic integration, the typical RIF effect was observed. Additional results revealed that the moderating effects of semantic integration are not mediated by explicit integration strategies.
147

Novel suppression methods in fire protection

Cabrera, Jan-Michael 16 February 2015 (has links)
The onset of fire within a compartment can pose a hazard to the occupants and the structure containing the compartment. Fire suppression systems aim to either extinguish or suppress an incipient fire before loss of life or damage to the structure can occur. The geometry and use of the compartment as well as the fuel packages within must be taken into account when choosing an appropriate fire suppression system. This thesis explores novel suppression methods inside of compartments. Los Alamos National Laboratories came to the University of Texas Fire Research Group (UTFRG) to characterize and investigate the fire danger inside of nuclear gloveboxes. The first suppression method discussed explores activation tests of a commercial automatic fire suppression system (Fire Foe [superscript TM]) containing heptaflouropropane (FE-36) fire suppressant conducted within a glovebox at the UTFRG's burn structure. Temperature and time to activation data of ten tests at four different fire sizes, three 13 kW, one 20 kW, three 25 kW, and three 50 kW, was taken. Gas temperatures from experiments were compared against NIST's Fire Dynamics Simulator (FDS) gas temperatures with good agreement. The time and spatially averaged net heat flux on a virtual Fire Foe [superscript TM] tube from the FDS simulations were passed to a thermo-physical, semi-empirical, sub-model to predict activation with poor agreement from experimental activation times. A Bayesian parameter inference was later run on the sub-model. While the Bayesian inference approach is able to match sub-model temperatures to experimental temperatures, some non-physical values for heat transfer coefficients and view factors were observed at the lower heat release rate fires. Micro combustion calorimetry (MCC) was used to determine heat of combustion of glovebox glove material and cone calorimetry tests were run to find ignition time versus incident heat flux. Using standard ignition time models, effective model parameters were calibrated. Thermal characterization of the glove material showed that the heat of combustion found from MCC was within the range of heats of combustion for other non-halogenated materials found in the literature. Analysis of the time to ignition tests showed that the glove material should be modeled as thermally thick when one would expect thin behavior. This behavior was attributed to possible heat losses from the back of the glove material. Dry water is expected to have similar suppression characteristics as water mist systems because the dry water particle sizes are on the order of water mist droplet sizes. The major benefit with dry water is the low pressures needed to drive the aerosol. An issue encountered with the dry water was flowing it in the way one would flow normal water. It was found that at low normal and shear stresses, the dry water clathrates would release the water held inside. A possible low shear delivery mechanism was discussed that avoids the ratholing effect. A continuous dry water production system was also designed. Filter loading tests were conducted to determine the quality of the dry water collected from the batch and continuous cases. It was observed that the ratio of water to silica for the continuous case reaches the batch value and is similar to results found in the literature. For the batch dry water it was observed that the particle size of the dried clathrates does vary with rotational speed of the blender and is independent of the type of water used (tap or deionized). / text
148

迴歸分析中Suppression與Enhancement現象之探討 / research suppression and enhancement phenomenon in regression

劉家齊 Unknown Date (has links)
自Horst (1941)提出suppressor變數一詞起,由於後續許多研究採用不盡相同思維之著眼點,也就衍生出許多不同定義的suppressor變數。Horst (1941)著重在判定係數的變化,Darlington (1968)、Conger (1974) 及 Cohen and Cohen (1975)則著重在迴歸係數的變化, Velicer (1978)則改用semipartial correlation coefficient來定義suppressor變數,再度將焦點轉回Horst (1941)的思維。Currie and Korabinski (1984)引進enhancement一詞,以便與suppression有所區分。 為了釐清這些紛擾的名詞定義,第二章、三章中,我們分別回顧enhancement與suppression兩現象。第四章中,我們針對enhancement、suppression兩種現象的關聯性,依據四種不同的面向進行比較。第五章,我們針對suppressor變數存在的情況下,藉由模擬實驗的方式,探討stepwise regression、forward selection、backward elimination三種變數選取方式的可能缺憾。第六章為總結。 / Since Horst (1941) introduced the term of suppressor variable, many different definitions of suppressor variables have appeared in literature. Originally, Horst (1941) based the definition on the coefficient of determination. Darlington (1968), Conger (1974) and Cohen and Cohen (1975) paid more attention on the regression coefficients instead. On the other hand, Velicer (1978) used semipartial correlation coefficient to define a suppressor variable, and directed the focus back to that of Horst (1941). In order to differentiate the two similarly related ideas, Currie and Korabinski (1984) proposed the term of enhancement to describe exclusively the situations reflected by the definition of Horst (1941) or Velicer (1978). In order to clarify the ambiguities resulting from various definitions of suppressor variable in literature, we first reviewed enhancement and suppression respectively in Chapters 2 and 3. In Chapter 4, we investigated their relationships from four different perspectives. In Chapter 5, we studied the possible drawbacks on using stepwise regression, forward selection, and backward elimination these three variable selection procedures on the presence of a suppressor variable. Conclusions are provided in Chapter 6.
149

Profiles of Everyday Thought Suppression

Ie, Amanda Yen Lin 06 June 2014 (has links)
The present research assessed whether levels of depression, anxiety and worry, obsessive-compulsive distress, and psychopathy were differentially related to distinct thought suppression profiles. As a means to achieving this goal, the Profiles of Everyday Thought Suppression (PETS) scale was constructed to measure the frequencies with which various target thoughts are suppressed. The PETS scale demonstrated good internal consistency and test-retest reliability, and scores were positively correlated with the general tendency to experience intrusions, the general tendency to suppress thoughts, neuroticism, and health complaints. Although the proportions of time people suppress thoughts was positively associated with the frequencies with which the thoughts are experienced, the strength of the associations differed across thought contents, suggesting that not all frequently experienced thoughts are invariably subject to suppression attempts. The frequency with which thoughts are generally suppressed was positively associated with overall levels of subclinical psychopathology experienced during the past month. When comparing across the various thought categories, results from multiple analytic strategies converged to suggest that specific subclinical psychopathological states are associated with particular sets of thoughts that are frequently suppressed. / Psychology
150

Development of a Measure of Craving Suppression

Upton, Brian T. 01 January 2015 (has links)
While there is evidence to support the efficacy of mindfulness-based treatment for substance use, the mechanisms through which they lead to therapeutic outcomes have received less attention. A growing body of literature suggests that the ways in which people respond to cravings may be an important mediator of change. Individuals with substance use problems may use them to cope with or avoid negative experiences, which could include the experience of craving itself. Thought suppression in particular has been investigated as a specific form of experiential avoidance, and findings suggest that thought suppression strategies may interfere with attempts to quit using substances. While mindfulness training should be expected to reduce the tendency to suppress or avoid cravings, evidence to support this expectation is limited, largely because no measures yet exist that assess the suppression of craving. Therefore, the purpose of the present study was to develop a self-report measure of the suppression of craving. Existing measures of other types of thought suppression and experiential avoidance were examined to identify items that could be adapted for use in the Craving Suppression Scale (CSS). To assist with the item development process, a focus group was also conducted at a local residential treatment facility. Participants were asked to discuss what they do when they are experiencing cravings and what thoughts go through their minds when cravings come up. Their responses were used to guide content development for the CSS items. Items were developed for two sub-scales: suppression of craving and beliefs about craving. Items were administered to a sample of inpatients in substance use treatment and an online sample of individuals reporting current or previous substance use problems (total N = 208). Factor analysis of the remaining items supported a two-factor structure for the CSS as hypothesized. Relationships were examined between the CSS and other measures of other forms of experiential avoidance/suppression, craving, and emotional distress. The CSS scales correlated well with other measures of suppression but had mixed relationships with other constructs of interest. Evidence for the validity and potential utility of the CSS are discussed along with theoretical and treatment implications.

Page generated in 0.0864 seconds