Constant Q and a fractal, stratifed Earth

Frequency dependent measurements of the quality factor Q typically show a constant behaviour for low frequencies and a positive power law dependence for higher frequencies. In particular, the constant Q pattern is usually explained using intrinsic attenuation models due to anelasticity with either a single or multiple superposed relaxation mechanisms - each with a particular resonance peak. However, in this study, I show using wave localisation theory that a constant Q may also be due to apparent attenuation due to scattering losses. Namely, this phenomenon occurs if the Earth displays fractal characteristics. Moreover, if fractal characteristics exist over a limited range of scales only, even an absorption band can be created - in accordance with observations. This indicates that it may be very difficult to distinguish between intrinsic and scattering attenuation on the basis of frequency dependent measurements of the quality factor only

Estimating anisotropy parameters and traveltimes in the tau-p domain

The presence of anisotropy influences many aspects of seismic wave propagation and has therefore implications for conventional processing schemes. To estimate the anisotropy, we need both forward modelling and inversion tools. Exact forward modelling in anisotropic media is generally done by raytracing. However, we present a new and fast method, using the tau-p transform, to calculate exact P and SV reflection moveout curves in stratified, laterally homogeneous, anisotropic media which requires no ray tracing. Results are exact even if the SV-waves display cusps. In addition, we show how the same method can be used for parameter estimation. Since inversion for anisotropic parameters is very nonunique, we develop expressions requiring only a reduced number of parameters. Nevertheless, predictions using these expressions are more accurate than Taylor series expansions and are also able to handle cusps in the SV traveltime curves. In addition, layer stripping is a linear process. Therefore, both effective (average) and local (interval) estimates can be obtained

Recognition and reconstruction of coherent energy with application to deep seismic reflection data

Reflections in deep seismic reflection data tend to be visible on only a limited number of traces in a common midpoint gather. To prevent stack degeneration, any noncoherent reflection energy has to be removed. In this paper, a standard classification technique in remote sensing is presented to enhance data quality. It consists of a recognition technique to detect and extract coherent energy in both common shot gathers and fi- nal stacks. This technique uses the statistics of a picked seismic phase to obtain the likelihood distribution of its presence. Multiplication of this likelihood distribution with the original data results in a “cleaned up” section. Application of the technique to data from a deep seismic reflection experiment enhanced the visibility of all reflectors considerably. Because the recognition technique cannot produce an estimate of “missing” data, it is extended with a reconstruction method. Two methods are proposed: application of semblance weighted local slant stacks after recognition, and direct recognition in the linear tau-p domain. In both cases, the power of the stacking process to increase the signal-to-noise ratio is combined with the direct selection of only specific seismic phases. The joint application of recognition and reconstruction resulted in data images which showed reflectors more clearly than application of a single technique

Traveltime and conversion-point computations and parameter estimation in layered, anisotropic media by tau-p transform

Anisotropy influences many aspects of seismic wave propagation and, therefore, has implications for conventional processing schemes. It also holds information about the nature of the medium. To estimate anisotropy, we need both forward modeling and inversion tools. Forward modeling in anisotropic media is generally done by ray tracing. We present a new and fast method using the tau-p transform to calculate exact reflection-moveout curves in stratified, laterally homogeneous, anisotropic media for all pure-mode and converted phases which requires no conventional ray tracing. Moreover, we obtain the common conversion points for both P-SV and P-SH converted waves. Results are exact for arbitrary strength of anisotropy in both HTI and VTI media (transverse isotropy with a horizontal or vertical symmetry axis, respectively). Since inversion for anisotropic parameters is a highly nonunique problem, we also develop expressions describing the phase velocities that require only a reduced number of parameters for both types of anisotropy. Nevertheless, resulting predictions for traveltimes and conversion points are generally more accurate than those obtained using the conventional Taylor-series expansions. In addition, the reduced-parameter expressions are also able to handle kinks or cusps in the SV traveltime curves for either VTI or HTI symmetry

Getting out of the joint:Cognitive bias modification and the treatment of substance use with detained young offenders

English Summary:This dissertation tests a brief, generally applicable treatment option for substance use in detained young offenders. A Cognitive Bias Modification (CBM) program is introduced, aiming to reduce alcohol and cannabis use, and evaluated in a randomized controlled trial (RCT). Attentional biases towards the substances were found but a 12-month follow-up reveals no significant reduction in substance use or delinquent recidivism.A review of the literature emphasizes the crucial role of motivation for treatment success and the challenges of achieving motivation in detained youth. The RCT was further complemented by a Motivational Interviewing (MI) module, designed to illustrate the link between substance use and personal problems, to boost motivation. The MI module, unfortunately failed to significantly alter participants' motivation or substance use behavior.The strategies employed to effectively recruit participants and ensure RCT completion rates within a regimented setting while maintaining ethical and scientific integrity are presented to aid future research.The dissertation concludes by advocating for tailored CBM protocols that align with individual goals. Acknowledging limitations, such as age-related factors and timing disparities in MI sessions, it prompts a reevaluation of the efficacy of detention-based interventions. The suggestion is made to pivot towards motivational enhancement, leveraging detention as an entry point for change, coupled with post-detention access to professional services. The project offers valuable insights, advocating for a nuanced approach that combines CBM, motivational enhancement, and traditional substance use treatments for detained young offenders.Dutch Summary: Deze dissertatie toetst een korte, algemeen toepasbare behandeloptie voor middelengebruik bij gedetineerde jongeren. Een Cognitive Bias Modification (CBM) programma wordt geïntroduceerd, met als doel vermindering van van alcohol en cannabis gebruik, en wordt geëvalueerd in een gerandomiseerde gecontroleerde trial (RCT). Er werden aandachtsbiassen gevonden ten opzichte van de middelen, maar een follow-up van 12 maanden laat geen significante vermindering zien in middelengebruik of delinquente recidive.Een literatuuronderzoek benadrukt de cruciale rol van motivatie voor het succes van de behandeling en de uitdagingen bij het bereiken van motivatie bij gedetineerde jongeren. De RCT werd verder aangevuld met een Motivational Interviewing (MI) module, ontworpen om de link tussen middelengebruik en persoonlijke problemen te illustreren en motivatie te stimuleren. Helaas slaagde de MI-module er niet in de motivatie of het middelengebruiksgedrag van de deelnemers significant te veranderen.De gebruikte strategieën om effectief deelnemers te werven en RCT-voltooiingspercentages te waarborgen binnen een streng gereguleerde setting, met behoud van ethische en wetenschappelijke integriteit, worden gepresenteerd om toekomstig onderzoek te ondersteunen.De dissertatie pleit voor op maat gemaakte CBM-protocollen die aansluiten bij individuele doelen. Met erkenning van beperkingen, zoals leeftijdsgerelateerde factoren en timing-discrepanties in MI-sessies, stimuleert het een heroverweging van de doeltreffendheid van op detentie-specifieke interventies. Het voorstel is om over te schakelen naar motivationele versterking, waarbij detentie wordt benut als een instappunt voor verandering, in combinatie met toegang tot professionele diensten na detentie. Het project biedt waardevolle inzichten en pleit voor een genuanceerde benadering die CBM, motivationele versterking en traditionele behandelingen voor gedetineerde jongeren combineert

Catalytic reforming : the reaction network

no abstract