Acoustic properties in travertines and their relation to porosity and pore types

Sonic velocities of Pleistocene travertines were measured under variable confining pressures. Combined with petrographical characteristics and petrophysical data, i.e. porosity, permeability and density, it was determined that travertine porosity, pore types and cementation control compressional-wave (Vp) and shear-wave velocity (Vs). At 40MPa confining pressures, Vp ranges between 3695 and 6097m/s and Vs between 2037 and 3140m/s. Velocity variations in travertines are, as with all carbonates, primarily linked to sample heterogeneity, i.e. differences in fabric, texture and porosity. They thus not necessarily emanate from changes in mineralogy or composition. Body wave velocities have a positive correlation with sample density and an inverse correlation with porosity. The travertines, sampled in extensional settings with normal faulting activity, define a specific compressional-wave velocity (y-axis) versus porosity (x-axis) equation, i.e. (log(y)=-0.0048x+3.7844) that differs from the Vp-porosity paths defined by marine carbonates. Acoustic wave velocities are higher for travertines than for marine carbonates. Travertine precipitates form rigid rock frames, often called framestone, with large primary pores. Marine carbonates on the other hand often consist of (cemented) transported sediments, resulting in a rock frame that permits slower wave propagation when compared to the continental limestones.Acoustic velocity variations are linked to variations in pore types. Mouldic pores (macropores) show faster wave propagation than expected from their total porosities. Microporosity, interlaminar and interpeloidal porosity result in slower acoustic velocities. Framework pores and micro-moulds are associated with lowered acoustic velocities, while vug porosity is found above, on and below the general velocity-porosity trend. Not only the pore type, but also pore shapes exert control on body wave velocities. Cuboid-and rod-like pore shapes increase the velocity, while plate-and blade-like pore shapes have a negative effect on the velocity. The study demonstrates how seismic sections in travertine systems can contain seismic reflections that are not caused by non-carbonate intercalations, but relate to geobody boundaries, in which the seismic expression is function of porosity, pore types and shapes. This study provides and relates petrophysical data, i.e. porosity, permeability and acoustic velocities of travertines and is of importance for the interpretation of seismic reflection data in subsurface continental carbonate reservoirs. © 2014 Elsevier Ltd

Physical and mechanical properties of carbonate sedimentary systems

Reijmer, J.J.G. [Promotor]Bertotti, G.V. [Copromotor

Acoustic properties in travertines and their relation to porosity and pore types

Sonic velocities of Pleistocene travertines were measured under variable confining pressures. Combined with petrographical characteristics and petrophysical data, i.e. porosity, permeability and density, it was determined that travertine porosity, pore types and cementation control compressional-wave (Vp) and shear-wave velocity (Vs). At 40 MPa confining pressures, Vp ranges between 3695 and 6097 m/s and Vs between 2037 and 3140 m/s. Velocity variations in travertines are, as with all carbonates, primarily linked to sample heterogeneity, i.e. differences in fabric, texture and porosity. They thus not necessarily emanate from changes in mineralogy or composition. Body wave velocities have a positive correlation with sample density and an inverse correlation with porosity. The travertines, sampled in extensional settings with normal faulting activity, define a specific compressional-wave velocity (y-axis) versus porosity (x-axis) equation, i.e. (log(y) = −0.0048x + 3.7844) that differs from the Vp-porosity paths defined by marine carbonates. Acoustic wave velocities are higher for travertines than for marine carbonates. Travertine precipitates form rigid rock frames, often called framestone, with large primary pores. Marine carbonates on the other hand often consist of (cemented) transported sediments, resulting in a rock frame that permits slower wave propagation when compared to the continental limestones.Acoustic velocity variations are linked to variations in pore types. Mouldic pores (macropores) show faster wave propagation than expected from their total porosities. Microporosity, interlaminar and interpeloidal porosity result in slower acoustic velocities. Framework pores and micro-moulds are associated with lowered acoustic velocities, while vug porosity is found above, on and below the general velocity-porosity trend. Not only the pore type, but also pore shapes exert control on body wave velocities. Cuboid-and rod-like pore shapes increase the velocity, while plate-and blade-like pore shapes have a negative effect on the velocity. The study demonstrates how seismic sections in travertine systems can contain seismic reflections that are not caused by non-carbonate intercalations, but relate to geobody boundaries, in which the seismic expression is function of porosity, pore types and shapes. This study provides and relates petrophysical data, i.e. porosity, permeability and acoustic velocities of travertines and is of importance for the interpretation of seismic reflection data in subsurface continental carbonate reservoirs

The impact of SCIAMACHY near-infrared instrument calibration on CH4 and CO total columns

The near-infrared spectra measured with the SCIAMACHY instrument on board the ENVISAT satellite suffer from several instrument calibration problems. The effects of three important instrument calibration issues on the retrieved methane (CH4) and carbon monoxide (CO) total columns have been investigated: the effects of the growing ice layer on the near-infrared detectors, the effects of the orbital variation of the instrument dark signal, and the effects of the dead/bad detector pixels. Corrections for each of these instrument calibration issues have been defined. The retrieved CH4 and CO total columns including these corrections show good agreement with CO measurements from the MOPITT satellite instrument and with CH4 model calculations by the chemistry transport model TM3. Using a systematic approach, it is shown that all three instrument calibration issues have a significant effect on the retrieved CH4 and CO total columns. However, the impact on the CH4 total columns is more pronounced than for CO, because of its smaller variability. Results for three different wavelength ranges are compared and show good agreement. The growing ice layer and the orbital variation of the dark signal show a systematic, but time-dependent effect on the retrieved CH4 and CO total columns, whereas the effect of the dead/bad pixels is rather unpredictable: some dead pixels show a random effect, some more systematic, and others no effect at all. The importance of accurate corrections for each of these instrument calibration issues is illustrated using examples where inaccurate corrections lead to a wrong interpretation of the results

Same-Day Discharge in Bariatric Surgery:A novel healthcare pathway

This thesis explored a novel healthcare pathway for bariatric surgery with same-day discharge (SDD) in response to ongoing challenges like staff shortages, the recent COVID-19 pandemic and a growing number of patients with obesity. The implementation of Enhanced Recovery After Bariatric Surgery (ERABS) in recent years has already resulted in a decrease in the length of hospital stay. This success gave the opportunity for further reducing admission time by introducing SDD. In this thesis, three crucial aspects of SDD were analyzed: patient selection, safety and complications, and patient satisfaction. In the first part of this thesis, focusing on patient selection, two studies were conducted. In Chapter 2, a study was performed to assess the feasibility of Roux-en-Y Gastric Bypass (RYGB) with SDD for patients with well-regulated obstructive sleep apnea using continuous positive airway pressure . The study demonstrated a high rate of successful discharge of 92% on the day of surgery. There were no severe complications in the first 48 hours after surgery, and no pulmonary complications were observed within the study population. The implementation of SDD after bariatric surgery began with RYGB, the most performed bariatric procedure in our hospital. As sleeve gastrectomy (SG) is the second most performed procedure, Chapter 3 investigated the feasibility of SDD for SG. The study revealed a high success rate of 90% for SDD with low complication rates in SG patients and no severe complications in the study population. Part 2 of this thesis explores safety and complications. Chapter 4 outlines a retrospective study involving 500 consecutive patients scheduled for RYGB with SDD, achieving a discharge success rate of 93%. There was a variety of reasons for overnight hospitalization, including pain and nausea. Bleeding emerged as the most common cause of readmission within the initial 48 hours following surgery. However, all these cases were managed conservatively. Chapter 5 presents a study based on the national database, comparing patients with similar characteristics. Patients who underwent SDD were compared to those who stayed overnight after bariatric surgery. The occurrence of severe complications, reoperations and mortality was found to be similar in both groups. However, SDD was associated with a higher 30-day readmission rate. The postoperative care protocol, or our “safety net”, was analyzed in Chapter 6. This safety net includes comprehensive patient education, simple remote monitoring and two consultations postoperatively. All early complications in this study were effectively detected. While the role of remote monitoring was limited, it is recommended to be integrated into the safety net. In a mixed-methods study in Chapter 7, patient satisfaction was evaluated using both validated questionnaires and interviews. Patients expressed great appreciation for SDD. A key strength of the SDD pathway was the role of healthcare providers. There was room for improvement regarding the information provision, particularly concerning the day of surgery. Additionally, not every medically eligible patient appeared suitable for this pathway, as responsibilities for detecting complications are partially shifted from healthcare providers to patients. In Chapter 8, the clinical implications of the conducted studies in this thesis are discussed. The chapter elaborates on the implementation of a SDD healthcare pathway, where several critical factors must be considered, including the implementation of ERABS as a prerequisite. It explains how to implement a similar SDD pathway. Future perspectives are discussed, including the role of digitalization. In this chapter it is concluded that the SDD pathway has proven to be safe and efficient, when strict criteria are followed, and that the pathway is appreciated by patients. Given the ongoing challenges in healthcare, bariatric surgery with SDD emerges as a potential solution to ensure the future sustainability of bariatric surgery

Normative data for the lower extremity functional scale (LEFS)

Background and purpose — The lower extremity functional scale (LEFS) is a well-known and validated instrument for measurement of lower extremity function. The LEFS was developed in a group of patients with various musculoskeletal disorders, and no reference data for the healthy population are available. Here we provide normative data for the LEFS. Methods — Healthy visitors and staff at 4 hospitals were requested to participate. A minimum of 250 volunteers had to be included at each hospital. Participants were excluded if they had undergone lower extremity surgery within 1 year of filling out the questionnaire, or were scheduled for lower extremity surgery. Normative values for the LEFS for the population as a whole were calculated. Furthermore, the influence of sex, age, type of employment, socioeconomic status, and history o