• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 147
  • 102
  • 39
  • 36
  • 16
  • 6
  • 4
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 407
  • 407
  • 99
  • 93
  • 56
  • 52
  • 41
  • 39
  • 36
  • 34
  • 32
  • 30
  • 29
  • 29
  • 27
  • 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.
101

Development of the Spectral-Analysis-of-Body-Waves (SABW) method for downhole seismic testing with boreholes or penetrometers

Kim, Changyoung 13 November 2012 (has links)
Downhole seismic testing and seismic cone penetration testing (SCPT) have shown little change since the 1990’s, with essentially the same sensors, sources, test procedures and analytical methods being used. In these tests, the time differences of first-arrivals or other reference points early in the time-domain signals have been used to calculate shear and compression wave velocities in soil and rock layers. This time-domain method requires an operator to pick the first arrival or other reference point of each seismic wave in the time record. Picking these reference points correctly is critical in calculating wave velocities. However, picking these points in time records is time consuming and is not always easy because of low signal-to-noise ratios, especially in the case of shear waves which arrive later in the time record. To avoid picking reference points, a cross-correlation method is sometimes applied to determine travel times of the seismic waves, especially in traditional downhole testing. One benefit of the cross-correlation method is that it can be automated. The cross-correlation method is not, however, appropriate for evaluation other body wave characteristics such as wave dispersion and material damping. An alternate approach is to use frequency-domain analysis methods which are well suited for evaluating time changes between all types of waveforms measured at spatially different points. In addition, frequency-domain methods can be automated and attenuation measurements can also be performed. Examples of such testing procedures with Rayleigh-type surface waves in geotechnical earthquake engineering are the Spectral-Analysis-of-Surface-Waves (SASW) and Multi-Channel-Analysis-of-Surface-Waves (MASW) methods. In this research, an automated procedure for calculating body wave velocities that is based on frequency-domain analysis is presented. The basis for and an automated procedure to calculated body wave dispersion is also presented. Example results showing shear wave velocity and material damping measurements in the SCPT are presented. The objective of this study is to improve downhole seismic tests with boreholes, cone penetrometers or flat-plate dilatometers by developing a frequency-domain analysis method which overcomes many of the disadvantages of time-domain analyses. The frequency-domain method is called the Spectral-Analysis-of-Body-Waves (SABW) method. The SABW method does not require an operator to pick the first-arrival or other reference times. As a result, the shear wave velocities and wave dispersion can be calculated in real time using the interpretation method with an automatic calculation procedure, thus reducing human subjectivity. Also, the SABW method can be used to determine additional information from the dispersion curves such as the material damping ratio and an estimate of soil type based on the dispersion relationship. In this research, field SCPT measurements are presented as an example to illustrate the potential of the SABW method. Measurements with shear waves are highlighted because these measurements are most often required in geotechnical earthquake engineering studies. / text
102

Development and evaluation of an inertial based pavement roughness measuring system

Hu, Fengxuan 01 June 2006 (has links)
Roughness is an important indicator of pavement riding comfort and safety. It is a condition indicator that should be carefully considered when evaluating primary pavements. At the same time, the use of roughness measurements plays a critical role in the pavement management system.There are many devices used for roughness evaluation. The major tools used for road roughness quantify are the road profilers. In the thesis research, in order to obtain useful pavement surface condition data for pavement evaluation, an inertial based pavement roughness measuring system was developed with the combination of modern sensor technology and computer technology. The research will focus on the development of new method to get the profile in order to improve the repeatability of the inertial based pavement roughness system, the hardware design and the software development which is used for data sampling and data analysis. Finally maximum entropy spectral analysis method was used to evalu ate the road profile spectrum.In order to get evaluate the accuracy and correction of the laser profiler system, different roughness devices (including Dipstick, direct type profiler and the laser profiler developed) were operated in the test sites. The research focused on several performance measures, such as repeatability (before and after new method analysis), impact of operating speed and sample interval, correlativity and etc. IRI from these devices were analyzed to evaluate the correlativity between these devices. Some regression models were developed in this research. Test results show that the new method can improve the repeatability of the profiler system. The laser profiler system has good repeatability and the operating speed and sample interval do not have a significant impact on the inertial based roughness measuring system. With the reliable results, the system is ready to be used in the field application within the speed and sample interval range. Through the spectrum an alysis, it shows that the spectrum has a qualitative relation with pavement roughness conditions.
103

Dvejetainės informacijos kodavimo naudojant bazinius skaidinius analizė: teoriniai ir praktiniai aspektai / Compression of binary data using identifying decomposition sequences: theoretical and practical aspects

Smolinskas, Mindaugas 13 January 2005 (has links)
A new approach (designed to lower computational complexity) to compression of finite binary data, based on the application of “exclusive-or” operation, is presented in the paper. The new concept of an identifying sequence, associated with a particular decomposition scheme, is introduced. A new heuristic algorithm for calculation of the identifying sequences has been developed. Two robust algorithms – for compressing and streaming the sequences (using a priori compiled decomposition tables), and for real time decoding of the compressed streams – were proposed and implemented. The experimental results confirmed that the developed approach gave a data compression effect on an ordinary computer system.
104

Applied Methods for Analysis of Economic Structure and Change

Anderstig, Christer January 1988 (has links)
The thesis comprises five papers and an introductory overview of applied models and methods. The papers concern interdependences and interrelations in models applied to empirical analyses of various problems related to production, consumption, location and trade. Among different definitions of 'structural analysis' one refers to the study of the properties of economic models on the assumption of invariant structural relations, this definition is close to what is aimed at in lire present case. Although the subjects cover widely differing aspects of the economic system, applied models and methods, i.e. entropy maximizing (information minimizing) models and random utility maximizing models, are in many cases closely connected. Tlic first paper reports on a regional input-ouput study applied to Norrbotten, Sweden. The paper is mainly concentrated on developing and estimating an econometric model, describing the structural interdependences in the Norrbotten economy. The chapter is composed of three parts. The first part concerns the theoretical basis of the model, the main fields of application and principal problems in connection with the estimation. The core of the estimated model is defined by the intersectoral dependences in the Norrbotten economy. This model can be viewed as a part of a more general model of the regional economy, and such a general model is briefly outlined. The second part reports on the collection and arranging of data, and the methods used for the estimation of the model. In the third part the results are presented. A special interest concerns the effects of production changes in the basic industries in the county, as to the expected impact on different industries and occupational groups. The second paper concerns some aspects of the problem of predicting trade flows in the forest sector. The model, based on information theory, is predicting current trade flows by adjusting the historical, a priori, trade flows to satisfy current export and import totals. In the third paper an entropy model is employed to decompose the interregional and intraregional employment change in Sweden and Stockholm, during the period 1960 - 1980, into effects attributed to regions (zones), industries, occupations and interaction effects. The fourth paper presents an empirical analysis of housing choice, based on individual data of households in Stockholm. The consumer choice is regarded as a complex choice from a finite set of discrete alternatives and a probabilistic choice mode! (multinomial logit) is employed, where secondary dwelling is included in the housing choice decision. In the final paper spectral analysis is used for identifying the significant components of cycle behaviour in time series of Swedish exports of forest products over a twenty year time period. / digitalisering@umu
105

FIELD SCALE BROMIDE TRANPORT AS A FUNCTION OF PRECIPITATION AMOUNT, INTENSITY AND APPLICATION TIME DELAY

Vasquez, Vicente 01 January 2010 (has links)
Rapid and deep transport of solutes in soils can potentially pollute groundwater resources. Field estimates of solute leaching depth based on randomized sampling provide extremely variable field average estimates that confound the treatment effects of the leaching study with the high spatial variation of soil hydraulic properties. The purpose of this study was to investigate the spatial scale of variation of solute (Bromide) leaching depth, and apply this scale of variation to study the leaching depth of Bromide as a function of a sinusoidal application of transport causing factors, i.e., rainfall amount, intensity and application time delay. Solute leaching depth varied over different spatial scales. The deepest leaching was observed on plots where the Br center of mass ranged from 19-30 cm depth. Deep leaching occurred with large quantities of low intensity precipitations (5.5 to 6 cm/day) and short time delays (≤ 17 hours), respectively. The hydraulic gradient presented cyclic variation at 8 m wavelength across the 10-30cm depth compartment. Spectral analysis indicated that spatial variation of the leaching depth was mainly affected by precipitation amount and intensity and only a small portion of the leaching depth variation was caused by time delay. Cross-spectral analysis identified common cyclic variation between the Br leaching depth and precipitation amount, intensity and time delay over 32, 32 and 8 m wavelengths, respectively. Simulated Br concentration over depth and horizontal distance and soil water matric potential ψm were in good agreement with experimental observations, the latter revealing a satisfactory Br and water mass balance.
106

UNDERSTANDING THE DEVELOPMENT OF INFANT FEEDING: A SPECTRAL ANALYSIS APPROACH

Vijaygopal, Pooja 01 January 2009 (has links)
Feeding problems in preterm neonates stem from complications of early delivery. Attainment of independent feeding is a prerequisite for Neonatal Intensive Care Unit (NICU) discharges. Some quantitative studies of infant feeding involve excessive amounts of time for data processing. Multivariate spectral analysis was used to minimize time for investigation of variability in these rhythms. Auto and Cross-spectral parameters of the rhythms were correlated with Gestational Age (GA), Postmenstrual Age (PMA), Birthweight (BW), Days of Life (DOL), and Time Since First Nipple feeding (TSFN). Auto-spectral analysis showed 25.55% increase in Bandwidth of suck (bw-su) for a 2-week increase in GA (DOL fixed) and 8.99% increase in bw-su for a 10-day increase in DOL (GA fixed). Crossspectral analysis showed a decrease of 0.158Hz of Bandwidth of Suck-Swallow (bw-SS) for a 2-week increase in GA for GA later than 28 weeks. For GA earlier than 28 weeks, peak coherence decreased by 0.774 for a 2-week increase in GA (PMA fixed) and decreased by 0.126 for a 2-week increase in PMA (GA fixed). The method describes the progression of feeding rhythms through correlations with clinical indexes, thus providing clinicians with an understanding of the development of infant feeding and helps predict long-term developmental outcomes.
107

Driver Modeling Based on Driving Behavior and Its Evaluation in Driver Identification

Miyajima, Chiyomi, Nishiwaki, Yoshihiro, Ozawa, Koji, Wakita, Toshihiro, Itou, Katsunobu, Takeda, Kazuya, Itakura, Fumitada January 2007 (has links)
No description available.
108

The effect of spectral tilt on infants' speech perception : implications for infants with hearing loss

Beach, Elizabeth F., University of Western Sydney, College of Arts, MARCS Auditory Laboratories January 2009 (has links)
Infants with hearing loss (HL) are being diagnosed and fitted with amplification earlier than ever before. In order to acquire speech and language abilities that are on par with their normal-hearing (NH) peers, hearing-impaired (HI) infants require amplification that provides appropriate exposure to the sounds of their native language. To date, no research has addressed this issue and thus, there is a need to examine the type of amplification that is most suitable for infants during the early stages of language acquisition. In this thesis, three different amplification types were compared: one that preserves the natural spectral shape of speech (unmodified speech); a second that emphasises high-frequency speech information (positive spectral tilt); and a third that emphasises low-frequency information (negative spectral tilt). NH infants were tested to examine how each of these amplification types affects speech perception and to explore whether infants at different stages of language acquisition find modified spectral tilt a help or hindrance in perceiving native-language speech contrasts. A visual habituation (VH) procedure was used to test 288 6- and 9-month-old NH infants on their ability to discriminate the high-frequency fricative contrast /f/- /s/; the mid-frequency approximant contrast /l/-/r/; and the low-frequency vowel contrast /5/-/N/ under modified spectral tilt conditions. For each speech contrast, 96 infants were tested in one of three conditions: (a) unmodified spectral tilt (n = 32); (b) with a positive 6 dB/octave spectral tilt (n = 32); or (c) with a negative 6 dB/octave spectral tilt (n = 32). The results showed that both 6- and 9-month-olds discriminated the three speech contrasts in the unmodified condition. However, when the contrasts were spectrally modified, a consistent developmental trend emerged. Six-month-olds’ discrimination performance improved when the spectral tilt modification amplified the relevant frequency information. That is, for the consonant contrasts (fricatives /f/-/s/ and approximants /l/-/r/) 6-month-olds performed best when high-frequency information was emphasised, whereas for the vowel contrast (/5/-/N/) the best discrimination performance was found when low-frequency information was enhanced. Nine-month-olds, on the other hand, showed no evidence of discriminating any of the contrasts when spectral tilt was modified. For all three contrasts, the older infants’ best discrimination performance was in the unmodified spectral tilt condition. The findings reflect the early stages of linguistic development. Six-month olds, whose acoustically driven speech perception operates in a language-general mode, demonstrated a broad-based ability to discriminate speech sounds. They not only accommodated speech with positive or negative spectral tilt, but a facilitation effect was observed when relevant frequency information was amplified. In contrast, 9-month-olds, whose perception is linguistically driven, found that spectral tilt modifications hinder speech perception. It seems that because older infants are attuning to native phonemic categories, their attention is constrained to native language spectral profiles only. Thus, even those spectral tilt modifications that should have been beneficial for perception were eschewed by 9-month-olds because they were incompatible with the older infants���� narrow focus on spectrally intact native speech sounds. Only NH infants were tested in this study, so it is not possible draw firm conclusions about amplification schemes until HI infants are tested too. Nevertheless, the results have a number of implications for infants with HL. The demonstration that spectral tilt modifications interfere with older NH infants’ speech perception suggests that future research should investigate whether HI infants also show this developmental pattern. That is, do HI infants progressively attune to the native language, and if so, does this affect their perception of spectrally modified speech sounds? Moreover, if HI infants are to attune to the native language and acquire speech and language in the same way as their NH peers, then the research reported here suggests that, throughout infancy, HI infants will need access to amplified speech that maintains the spectral shape of natural speech. Thus, the current research demonstrates, for the first time, a developmental difference in the way that infants perceive spectrally modified speech, one that is closely linked to the infant’s stage of native-language attunement. This research provides a solid foundation on which to conduct further research with HI infants and offers preliminary suggestions with regard to amplification and intervention to ensure that HI infants have the opportunity to emulate the native-language attunement process and subsequently achieve language development outcomes comparable with their NH peers. / Doctor of Philosophy (PhD)
109

Spectral analysis and resolving spatial ambiguities in human sound localization

Jin, Craig January 2001 (has links)
Doctor of Philosophy / This dissertation provides an overview of my research over the last five years into the spectral analysis involved in human sound localization. The work involved conducting psychophysical tests of human auditory localization performance and then applying analytical techniques to analyze and explain the data. It is a fundamental thesis of this work that human auditory localization response directions are primarily driven by the auditory localization cues associated with the acoustic filtering properties of the external auditory periphery, i.e., the head, torso, shoulder, neck, and external ears. This work can be considered as composed of three parts. In the first part of this work, I compared the auditory localization performance of a human subject and a time-delay neural network model under three sound conditions: broadband, high-pass, and low-pass. A “black-box” modeling paradigm was applied. The modeling results indicated that training the network to localize sounds of varying center-frequency and bandwidth could degrade localization performance results in a manner demonstrating some similarity to human auditory localization performance. As the data collected during the network modeling showed that humans demonstrate striking localization errors when tested using bandlimited sound stimuli, the second part of this work focused on human sound localization of bandpass filtered noise stimuli. Localization data was collected from 5 subjects and for 7 sound conditions: 300 Hz to 5 kHz, 300 Hz to 7 kHz, 300 Hz to 10 kHz, 300 Hz to 14 kHz, 3 to 8 kHz, 4 to 9 kHz, and 7 to 14 kHz. The localization results were analyzed using the method of cue similarity indices developed by Middlebrooks (1992). The data indicated that the energy level in relatively wide frequency bands could be driving the localization response directions, just as in Butler’s covert peak area model (see Butler and Musicant, 1993). The question was then raised as to whether the energy levels in the various frequency bands, as described above, are most likely analyzed by the human auditory localization system on a monaural or an interaural basis. In the third part of this work, an experiment was conducted using virtual auditory space sound stimuli in which the monaural spectral cues for auditory localization were disrupted, but the interaural spectral difference cue was preserved. The results from this work showed that the human auditory localization system relies primarily on a monaural analysis of spectral shape information for its discrimination of directions on the cone of confusion. The work described in the three parts lead to the suggestion that a spectral contrast model based on overlapping frequency bands of varying bandwidth and perhaps multiple frequency scales can provide a reasonable algorithm for explaining much of the current psychophysical and neurophysiological data related to human auditory localization.
110

Estudo da sensibilidade barorreflexa e sua relação com a produção de citocinas inflamatórias no processo de envelhecimento

Milan, Juliana Cristina 21 August 2014 (has links)
Made available in DSpace on 2016-08-17T18:39:51Z (GMT). No. of bitstreams: 1 6222.pdf: 2879821 bytes, checksum: 010a3c6abf3b0c6f2ec81ebf9ff59ef0 (MD5) Previous issue date: 2014-08-21 / Universidade Federal de Sao Carlos / Aging causes changes in several human subsystems such as the cardiovascular and immune systems. The objective of this study was to evaluate the relationship between baroreflex function through linear algorithm (cross-spectral analysis) and proinflammatory cytokines in the aging process and also assess the baroreflex sensitivity, TNF-α, IL-6 and hsCRP in different ages and in the aging process. One hundred and ten apparently healthy subjects divided into 5 groups with 22 individuals each, according to age were evaluated: 21-30 years, 30-40 years, 40-50 years, 50-60 years, 60-70 years. The experimental protocol consisted of a blood samples collection for analysis of inflammatory markers and in the same day were collected ECG, blood pressure and respiratory movements for 15 minutes in the supine position and in standing position, after the active postural change for 15 minutes. For the analysis of baroreflex sensitivity cross spectral analysis (coherence, phase and gain) was used and ELISA method for analysis of TNF-α and IL-6 was used. Data were analyzed using analysis of variance one-way ANOVA test with Tukey test post-hoc or Kruskal-Wallis oneway ANOVA with Dunn's post-hoc according to the normality of the data and the Spearman correlation test. The level of significance for the tests was 5%. The main results were: 1) reduced baroreflex sensitivity during the aging process; 2) increased levels of inflammatory markers in the aging process; 3) negative correlation between IL-6 and BF gain and phase; 4) negative relationship between hsCRP and coherence, phase and gain in BF. It can be concluded that the human natural aging causes a loss of baroreflex sensitivity and increased serum levels of inflammatory markers studied, although the decrease in baroreflex sensitivity as function of the decreasing of vagal autonomic function occurred in the 41-50 age range, and only in the next age was observed changes in inflammatory markers. / O envelhecimento causa alterações em diversos subsistemas humanos como o cardiovascular e imunológico. O objetivo deste trabalho foi avaliar a relação entre a função barorreflexa, por meio de algoritmo linear (análise espectral cruzada) e citocinas próinflamatórias no processo de envelhecimento e ainda, avaliar a sensibilidade barorreflexa, IL- 6, TNF-α e PCRus em diversas faixas etárias e no processo de envelhecimento. Foram avaliados 110 indivíduos aparentemente saudáveis divididos em 5 grupos com 22 indivíduos cada, de acordo com a faixa etária: 21-30 anos, 30-40 anos, 40-50 anos, 50-60 anos, 60-70 anos. O protocolo experimental consistiu em uma coleta de amostras de sangue para a análise dos marcadores inflamatórios e no mesmo dia foram coletados o eletrocardiograma (ECG), a pressão arterial de pulso e a respiração por 15 minutos na postura supina, logo após foi realizada a mudança postural ativa de supino para ortostatismo, permanecendo 15 minutos nesta posição a coleta de sangue. Para a análise da sensibilidade barorreflexa foi utilizada a analise espectral cruzada e o método ELISA para análise das citocinas TNF-α e IL-6. Os dados foram analisados por meio do teste de análise de variância ANOVA one-way com posthoc de Tukey ou Kruskal-Wallis ANOVA one-way com post-hoc de Dunn s de acordo com a normalidade dos dados e teste de Correlação de Spearman. O nível de significância estabelecido para os testes foi de 5%. Os principais resultados foram: 1) redução da sensibilidade barorreflexa durante o processo de envelhecimento; 2) aumento dos níveis dos marcadores inflamatórios no processo de envelhecimento; 3) relação negativa entre a IL-6 e fase e ganho em BF; 4) relação negativa entre PCRus e coerência, fase e ganho em BF. Podese concluir que o envelhecimento natural humano causa a redução da sensibilidade barorreflexa e aumento dos níveis séricos dos marcadores inflamatórios estudados, ainda a diminuição da sensibilidade barorreflexa em consequência da diminuição da função autonômica vagal correu na faixa etária 41-50 e somente na faixa etária seguinte foi observada alterações nos marcadores inflamatórios.

Page generated in 0.0619 seconds