951 resultados para finite-difference time-domain (FDTD) method
Resumo:
A major issue in the application of waveform inversion methods to crosshole ground-penetrating radar (GPR) data is the accurate estimation of the source wavelet. Here, we explore the viability and robustness of incorporating this step into a recently published time-domain inversion procedure through an iterative deconvolution approach. Our results indicate that, at least in non-dispersive electrical environments, such an approach provides remarkably accurate and robust estimates of the source wavelet even in the presence of strong heterogeneity of both the dielectric permittivity and electrical conductivity. Our results also indicate that the proposed source wavelet estimation approach is relatively insensitive to ambient noise and to the phase characteristics of the starting wavelet. Finally, there appears to be little to no trade-off between the wavelet estimation and the tomographic imaging procedures.
Resumo:
After a rockfall event, a usual post event survey includes qualitative volume estimation, trajectory mapping and determination of departing zones. However, quantitative measurements are not usually made. Additional relevant quantitative information could be useful in determining the spatial occurrence of rockfall events and help us in quantifying their size. Seismic measurements could be suitable for detection purposes since they are non invasive methods and are relatively inexpensive. Moreover, seismic techniques could provide important information on rockfall size and location of impacts. On 14 February 2007 the Avalanche Group of the University of Barcelona obtained the seismic data generated by an artificially triggered rockfall event at the Montserrat massif (near Barcelona, Spain) carried out in order to purge a slope. Two 3 component seismic stations were deployed in the area about 200 m from the explosion point that triggered the rockfall. Seismic signals and video images were simultaneously obtained. The initial volume of the rockfall was estimated to be 75 m3 by laser scanner data analysis. After the explosion, dozens of boulders ranging from 10¿4 to 5 m3 in volume impacted on the ground at different locations. The blocks fell down onto a terrace, 120 m below the release zone. The impact generated a small continuous mass movement composed of a mixture of rocks, sand and dust that ran down the slope and impacted on the road 60 m below. Time, time-frequency evolution and particle motion analysis of the seismic records and seismic energy estimation were performed. The results are as follows: 1 ¿ A rockfall event generates seismic signals with specific characteristics in the time domain; 2 ¿ the seismic signals generated by the mass movement show a time-frequency evolution different from that of other seismogenic sources (e.g. earthquakes, explosions or a single rock impact). This feature could be used for detection purposes; 3 ¿ particle motion plot analysis shows that the procedure to locate the rock impact using two stations is feasible; 4 ¿ The feasibility and validity of seismic methods for the detection of rockfall events, their localization and size determination are comfirmed.
Resumo:
A number of geophysical methods, such as ground-penetrating radar (GPR), have the potential to provide valuable information on hydrological properties in the unsaturated zone. In particular, the stochastic inversion of such data within a coupled geophysical-hydrological framework may allow for the effective estimation of vadose zone hydraulic parameters and their corresponding uncertainties. A critical issue in stochastic inversion is choosing prior parameter probability distributions from which potential model configurations are drawn and tested against observed data. A well chosen prior should reflect as honestly as possible the initial state of knowledge regarding the parameters and be neither overly specific nor too conservative. In a Bayesian context, combining the prior with available data yields a posterior state of knowledge about the parameters, which can then be used statistically for predictions and risk assessment. Here we investigate the influence of prior information regarding the van Genuchten-Mualem (VGM) parameters, which describe vadose zone hydraulic properties, on the stochastic inversion of crosshole GPR data collected under steady state, natural-loading conditions. We do this using a Bayesian Markov chain Monte Carlo (MCMC) inversion approach, considering first noninformative uniform prior distributions and then more informative priors derived from soil property databases. For the informative priors, we further explore the effect of including information regarding parameter correlation. Analysis of both synthetic and field data indicates that the geophysical data alone contain valuable information regarding the VGM parameters. However, significantly better results are obtained when we combine these data with a realistic, informative prior.
Resumo:
Cross-hole radar tomography is a useful tool for mapping shallow subsurface electrical properties viz. dielectric permittivity and electrical conductivity. Common practice is to invert cross-hole radar data with ray-based tomographic algorithms using first arrival traveltimes and first cycle amplitudes. However, the resolution of conventional standard ray-based inversion schemes for cross-hole ground-penetrating radar (GPR) is limited because only a fraction of the information contained in the radar data is used. The resolution can be improved significantly by using a full-waveform inversion that considers the entire waveform, or significant parts thereof. A recently developed 2D time-domain vectorial full-waveform crosshole radar inversion code has been modified in the present study by allowing optimized acquisition setups that reduce the acquisition time and computational costs significantly. This is achieved by minimizing the number of transmitter points and maximizing the number of receiver positions. The improved algorithm was employed to invert cross-hole GPR data acquired within a gravel aquifer (4-10 m depth) in the Thur valley, Switzerland. The simulated traces of the final model obtained by the full-waveform inversion fit the observed traces very well in the lower part of the section and reasonably well in the upper part of the section. Compared to the ray-based inversion, the results from the full-waveform inversion show significantly higher resolution images. At either side, 2.5 m distance away from the cross-hole plane, borehole logs were acquired. There is a good correspondence between the conductivity tomograms and the natural gamma logs at the boundary of the gravel layer and the underlying lacustrine clay deposits. Using existing petrophysical models, the inversion results and neutron-neutron logs are converted to porosity. Without any additional calibration, the values obtained for the converted neutron-neutron logs and permittivity results are very close and similar vertical variations can be observed. The full-waveform inversion provides in both cases additional information about the subsurface. Due to the presence of the water table and associated refracted/reflected waves, the upper traces are not well fitted and the upper 2 m in the permittivity and conductivity tomograms are not reliably reconstructed because the unsaturated zone is not incorporated into the inversion domain.
Resumo:
Este estudo visou à obtenção das curvas de calibração de um equipamento de TDR (Time Domain Reflectometry) em cinco solos da região de Piracicaba, SP, e testou a adequação da calibração interna do equipamento e das curvas genéricas de calibração. As curvas ajustadas, em cada solo separadamente, apresentaram coeficientes de determinação (R²) da ordem de 0,99, e a curva ajustada para o conjunto de dados dos cinco solos apresentou R² = 0,976. A análise de erros-padrão de estimativa mostrou que as curvas genéricas não se prestam às aplicações mais sensíveis, tais como na determinação absoluta do conteúdo de água do solo. Os testes de comparação entre as curvas ajustadas, a curva genérica e a curva embutida no equipamento mostraram que a primeira é superior às demais. O estudo mostrou, também, que a curva de calibração embutida no equipamento é inadequada para as determinações de umidade nos cinco solos estudados.
Resumo:
Recent ink dating methods focused mainly on changes in solvent amounts occurring over time. A promising method was developed at the Landeskriminalamt of Munich using thermal desorption (TD) followed by gas chromatography / mass spectrometry (GC/MS) analysis. Sequential extractions of the phenoxyethanol present in ballpoint pen ink entries were carried out at two different temperatures. This method is applied in forensic practice and is currently implemented in several laboratories participating to the InCID group (International Collaboration on Ink Dating). However, harmonization of the method between the laboratories proved to be a particularly sensitive and time consuming task. The main aim of this work was therefore to implement the TD-GC/MS method at the Bundeskriminalamt (Wiesbaden, Germany) in order to evaluate if results were comparable to those obtained in Munich. At first validation criteria such as limits of reliable measurements, linearity and repeatability were determined. Samples were prepared in three different laboratories using the same inks and analyzed using two TDS-GC/MS instruments (one in Munich and one in Wiesbaden). The inter- and intra-laboratory variability of the ageing parameter was determined and ageing curves were compared. While inks stored in similar conditions yielded comparable ageing curves, it was observed that significantly different storage conditions had an influence on the resulting ageing curves. Finally, interpretation models, such as thresholds and trend tests, were evaluated and discussed in view of the obtained results. Trend tests were considered more suitable than threshold models. As both approaches showed limitations, an alternative model, based on the slopes of the ageing curves, was also proposed.
Resumo:
In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya"s known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection.
Resumo:
The formation and semiclassical evaporation of two-dimensional black holes is studied in an exactly solvable model. Above a certain threshold energy flux, collapsing matter forms a singularity inside an apparent horizon. As the black hole evaporates the apparent horizon recedes and meets the singularity in a finite proper time. The singularity emerges naked, and future evolution of the geometry requires boundary conditions to be imposed there. There is a natural choice of boundary conditions which matches the evaporated black hole solution onto the linear dilaton vacuum. Below the threshold energy flux no horizon forms and boundary conditions can be imposed where infalling matter is reflected from a timelike boundary. All information is recovered at spatial infinity in this case.
Resumo:
In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya"s known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection.
Resumo:
Raaka-aineen hiukkaskoko on lääkekehityksessä keskeinen materiaaliparametri. Lääkeaineen partikkelikoko vaikuttaa moneen lääketuotteen tärkeään ominaisuuteen, esimerkiksi lääkkeen biologiseen hyväksikäytettävyyteen. Tässä diplomityössä keskityttiin jauhemaisten lääkeaineiden hiukkaskoon määrittämiseen laserdiffraktiomenetelmällä. Menetelmä perustuu siihen, että partikkeleista sironneen valon intensiteetin sirontakulmajakauma on riippuvainen partikkelien kokojakaumasta. Työn kirjallisuusosassa esiteltiin laserdiffraktiomenetelmän teoriaa. PIDS (Polarization Intensity Differential Scattering) tekniikka, jota voidaan käyttää laserdiffraktion yhteydessä, on myös kuvattu kirjallisuusosassa. Muihin menetelmiin perustuvista analyysimenetelmistä tutustuttiin mikroskopiaan sekä aerodynaamisen lentoajan määrittämiseen perustuvaan menetelmään. Kirjallisuusosassa esiteltiin myös partikkelikoon yleisimpiä esitystapoja. Työn kokeellisen osan tarkoituksena oli kehittää ja validoida laserdiffraktioon perustuva partikkelikoon määritysmenetelmä tietylle lääkeaineelle. Menetelmäkehitys tehtiin käyttäen Beckman Coulter LS 13 320 laserdiffraktoria. Laite mahdollistaa PIDS-tekniikan käytön laserdiffraktiotekniikan ohella. Menetelmäkehitys aloitettiin arvioimalla, että kyseinen lääkeaine soveltuu parhaiten määritettäväksi nesteeseen dispergoituna. Liukoisuuden perusteella väliaineeksi valittiin tällä lääkeaineella kyllästetty vesiliuos. Dispergointiaineen sekä ultraäänihauteen käyttö havaittiin tarpeelliseksi dispergoidessa kyseistä lääkeainetta kylläiseen vesiliuokseen. Lopuksi sekoitusnopeus näytteensyöttöyksikössä säädettiin sopivaksi. Validointivaiheessa kehitetyn menetelmän todettiin soveltuvan hyvin kyseiselle lääkeaineelle ja tulosten todettiin olevan oikeellisia sekä toistettavia. Menetelmä ei myöskään ollut herkkä pienille häiriöille.
Resumo:
Diplomityö on tehty osana ETX-tutkimushanketta: 'Volyymiteholähteen suunnittelumetodien kehitys ja optimointi DFM-viitekehyksessä'. Työssä suunnitellaan hakkuriteholähteelle säätäjä. Tähän suunnittelun sektoriin syventyminen on teollisuudessa jäänyt monesti vähälle. Säätö on tavallisesti ajan puutteen ja apuvälineiden käytön osaamattomuuden tai puuttumisen takia suunniteltu kokeilemalla. Työssä muodostetaan jännitemuotoisesti säädetylle hakkurille piensignaalimallilla linearisoidut siirtofunktiot, joiden perusteella voidaan tarkastella hakkurin stabiilisuutta takaisinkytketyssä säätösilmukassa. Stabiiliustarkastelu tehdään taajuustasossa käyttäen Bode-kuvaajia. Näiden kuvaajien perusteella viritetään järjestelmään säätäjä. Säätäjän toimintaa aikatasossa tarkastellaan simuloimalla ja reaalisen laitteen toimimista laboratorioprototyypin avulla. Tulosten perusteella voidaan todeta, että jännitemuotoisella säädöllä flyback-hakkuri saadaan nopeaksi epäjatkuvalla käämivirralla. Mikäli halutaan hakkurin toimivan jatkuvalla käämivirralla, on syytä käyttää muita säätömenetelmiä, esimerkiksi huippuvirtasäätöä.
Resumo:
Among the tools proposed to assess the athlete's "fatigue," the analysis of heart rate variability (HRV) provides an indirect evaluation of the settings of autonomic control of heart activity. HRV analysis is performed through assessment of time-domain indices, the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (RMSSD) measured during short (5 min) recordings in supine position upon awakening in the morning and particularly the logarithm of RMSSD (LnRMSSD) has been proposed as the most useful resting HRV indicator. However, if RMSSD can help the practitioner to identify a global "fatigue" level, it does not allow discriminating different types of fatigue. Recent results using spectral HRV analysis highlighted firstly that HRV profiles assessed in supine and standing positions are independent and complementary; and secondly that using these postural profiles allows the clustering of distinct sub-categories of "fatigue." Since, cardiovascular control settings are different in standing and lying posture, using the HRV figures of both postures to cluster fatigue state embeds information on the dynamics of control responses. Such, HRV spectral analysis appears more sensitive and enlightening than time-domain HRV indices. The wealthier information provided by this spectral analysis should improve the monitoring of the adaptive training-recovery process in athletes.
Resumo:
Among the tools proposed to assess the athlete's "fatigue," the analysis of heart rate variability (HRV) provides an indirect evaluation of the settings of autonomic control of heart activity. HRV analysis is performed through assessment of time-domain indices, the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (RMSSD) measured during short (5 min) recordings in supine position upon awakening in the morning and particularly the logarithm of RMSSD (LnRMSSD) has been proposed as the most useful resting HRV indicator. However, if RMSSD can help the practitioner to identify a global "fatigue" level, it does not allow discriminating different types of fatigue. Recent results using spectral HRV analysis highlighted firstly that HRV profiles assessed in supine and standing positions are independent and complementary; and secondly that using these postural profiles allows the clustering of distinct sub-categories of "fatigue." Since, cardiovascular control settings are different in standing and lying posture, using the HRV figures of both postures to cluster fatigue state embeds information on the dynamics of control responses. Such, HRV spectral analysis appears more sensitive and enlightening than time-domain HRV indices. The wealthier information provided by this spectral analysis should improve the monitoring of the adaptive training-recovery process in athletes.
Resumo:
Tausta: Polyneuropatia (PNP) on ääreishermoston sairaus, joka aiheuttaa laaja-alaisia, yleensä symmetrisiä vaurioita ääreishermostossa. PNP:aan johtavia syitä on satoja. Tavoitteet: Löytää parhaat neurofysiologiset menetelmät uremian, myelooman hoidossa käytettävän talidomidin sekä Fabryn taudin aiheuttaman PNP:n diagnosoimiseksi. Fabryn taudissa tutkin lisäksi ohutsäieneuropatian aiheuttamia neuropatologisia löydöksiä iholta otetusta koepalasta. Tutkimuksissa kartoitettiin lisäksi PNP:n aiheuttamien subjektiivisten oireiden korrelaatio neurofysiologisten ja neuropatologisten löydösten kanssa. Munuaisten vajaatoimintaa sairastavilla potilailla tavoitteena oli tutkia dialyysihoidon tehon vaikutusta autonomisen hermoston toimintaan sekä yhden dialyysikerran vaikutusta neurofysiologisiin löydöksiin. Aineisto ja menetelmät: I: Tutkittiin 21 uremiapotilaan sensoristen ja motoristen hermojen vasteet, värinä- sekä lämpötuntokynnykset ennen ja jälkeen hemodialyysin. Subjektiiviset PNP oireet kartoitettiin PNP oireita kysyvillä kaavakkeella. II:12 talidomidi hoitoa saavaa myeloomapotilasta, tutkimuksen menetelmät olivat samat kuin tutkimuksessa I. III: 12 Fabryn tautia sairastavaa potilasta, edellä mainittujen neurofysiologisten tutkimusten lisäksi potilailta otettiin ihobiopsia säären alueelta. Ihobiopsiasta laskettiin ohuiden hermosyiden määrä koepalan värjäyksen jälkeen. Subjektiiviset PNP oireet kartoitettiin kyselykaavakkeella. Sydämen sykevaihtelu tutkittiin levossa taajuustason analyysillä. IV: 32 uremiapotilaan autonomisen hermoston toimintaa tutkittiin sydämen sykevaihtelun aikatason analysillä, paksujen myelinoituneiden säikeiden toimintaa tutkittiin perifeeristen sensoristen hermojen mittauksilla toistetusti noin 2.9 vuoden aikana. Tulokset: Ureemisen PNP:n diagnostiikassa herkimmät tutkimukset ovat F-aaltojen parametrit alaraajojen motorisista hermoista, värinätuntokynnys alaraajoista sekä suralishermon amplitudi. Positiiviset PNP oireet uremiassa korreloivat värinätunto-kynnyksen sekä sensoristen hermojen neurografialöydösten kanssa. Neurofysiologisten tutkimusten ajankohdalla dialyysiajankohtaan nähden ei ole merkitystä. Talidomidi-PNP on pääasiassa sensorinen, mutta motoriset syyt ovat lievästi vaurioituneet. Talidomidi PNP:ssa subjektiiviset oireet korreloivat huonosti neurofysiologisten löydösten kanssa. Fabryn taudissa naisilla on oletettua enemmän ohutsäieneuropatian aiheuttamia oireita ja löydöksiä. Paksujen säikeiden löydöksiä ei tullut esiin. Ohutsäieneuropatian diagnostiikassa ihobiopsia ja kvantitatiiviset tuntokynnysmittaustestit täydentävät toisiaan. Tehokas dialyysi parantaa autonomisen hermoston toimintaa uremiapotilailla. Päätelmät: Erityyppisten polyneuropatioiden diagnostiikassa pitää etukäteen valita PNP tyypille oikeat tutkimusmenetelmät raskaiden tutkimuspatterien vähentämiseksi sekä diagnostiikan parantamiseksi. PNP:n aiheuttamat oireet ja kliiniset löydökset pitää aina tutkia, mutta yksin ne eivät ole herkkiä PNP:n diagnostiikassa.
Resumo:
Una de las técnicas analíticas más novedosas en el ámbito de la metodología observacional es la que permite la detección de T-patterns (estructuras regulares de conducta) mediante el software THEME, que analiza datos observacionales en búsqueda de relaciones de intervalo crítico en sentido ascendente (desde T-pattern simples, dos eventos que se relacionan en un primer nivel, a T-patterns complejos constituidos por diferentes eventos relacionados en distintos niveles). En el presente artículo se analiza esta cuestión, la degradación de los T-patterns, que hasta el momento ha sido puntualmente estudiada. Para ello, se utiliza el muestreo observacional constituido por el conjunto de las secuencias que acaban en gol (n= 23) protagonizadas por el F.C. Barcelona durante el Play Off Final de la liga española 2012-13 de fútbol sala. De esta forma este trabajo satisface un segundo objetivo, en este caso disciplinar, de analizar la e'cacia en la construcción de la fase ofensiva en el fútbol sala; habiéndose tipi'cado que las secuencias que 'nalizan en gol se caracterizan por conseguir, mediante juego combinativo, un lanzamiento desde sector de'nición-corredor central.