Seismic surveys along subduction zones have identified anomalously high ratio of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust that are possibly due to the presence of pore water. ...Such interpretations postulate that the pore structure is homogeneous at the scale of the seismic wavelength. Here we present the first statistical evidence of a heterogeneous pore structure in oceanic crust at scales larger than laboratory samples. The spatial correlation of measured bulk density profiles of the crustal section of the Samail ophiolite suggests that the pore structure is heterogeneous at scales smaller than ∼1 m. Wave‐induced fluid flow cannot follow the loading during the seismic wave propagation at this estimated heterogeneity, which implies that fluid‐filled microscopic pores and cracks have a limited impact on the observed high VP/VS anomalies in the subducting oceanic crust. Large‐scale cracks may therefore play an important role in shaping these anomalies.
Plain Language Summary
Seismic studies along subduction zones have identified unusually high ratios of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust, which indicates the presence of water‐filled cracks and pores. The close link between pore water and local seismic activity highlights the importance of quantitatively interpreting these seismic anomalies in terms of pore characteristics. Previous interpretations have assumed that the microscopic pore structure is quite homogeneous, even at macroscopic scales as large as the seismic wavelength. However, our analysis of a bulk density profile of the crustal section of the Samail ophiolite, Oman, which is a fossilized oceanic plate preserved on land, indicates that the pore structure is more heterogeneous than previously assumed. This means that the fluid flow within the unit volume that represents the macroscopic physical properties of the rock cannot follow the wave‐induced loading during seismic wave propagations. This results in a relatively small impact of water on the seismic velocity, as inferred from theoretical models that predict the effective elastic properties of rock containing fluid‐filled cracks. Therefore, microscopic cracks may not have a large impact on the high VP/VS values of subducting oceanic crust, whereas large‐scale cracks may play a more significant role.
Key Points
The bulk density of the crustal section of the Samail ophiolite is more spatially heterogeneous than previously assumed
The effect of fluid‐saturated microcracks on low‐frequency seismic velocities is modeled as an unrelaxed condition for this heterogeneity
The high VP/VS anomaly in the subducting oceanic crust can be explained by both microcracks and large‐scale cracks
To assess the paleo‐permeability structure of oceanic crust, we used 3‐D X‐ray Computed Tomography (XCT) images to quantify the distribution and geometry of mineral veins in core samples from Oman ...Drilling Project Holes GT1A, GT2A, and GT3A, which correspond to the upper to lower crustal sections of the Samail ophiolite. We developed a new method that automatically detects veins in the XCT core images based on iterative adaption of the two‐step Hough transform combined with multiscale Hessian filtering for identifying an elongate structure. Application of the developed method allowed us to identify the geometry and Computed Tomography number of more than 1500 veins with millimeter‐scale apertures in core sections with a total length of ∼1,200 m. High‐CT (HCT) veins in the drilled cores can be related to relatively high‐temperature fluid circulation near the mid‐ocean ridge, whereas Low‐CT (LCT) veins can be related to subsequent low‐temperature fluid circulation. Applying fracture fluid‐flow models to the geometric information for the detected veins, we found that the HCT and LCT vein systems both yielded bulk permeability of 10−13–10−9 m2 for each hole. This indicates that millimeter‐wide fractures can control crustal‐scale permeability, even in the lower oceanic crust. However, these vein systems show different depth dependencies and anisotropies of permeability, possibly reflecting the different spatial variations of high‐ and low‐temperature fluid circulation in oceanic crust.
Plain Language Summary
Water transported through fractures in the oceanic crust plays a key role in various geologic processes, such as global transfers of heat and elements moving with fluid. Such fractures are preserved in crustal rocks as mineral veins; therefore, the geometries of the veins can be used to estimate the paleo‐permeability of the fractured rocks. During this study, we investigated the distribution and geometry of veins in core samples of oceanic crust from the Samail ophiolite in Oman to determine its paleo‐permeability structure. The ophiolite represents fragments of ancient oceanic lithosphere obducted onto the continental margin. We quantified three‐dimensional geometric and material information for the veins using 3‐D X‐ray Computed Tomography images of the core samples. Applying fracture fluid‐flow models to the vein data, we found that the oceanic crust had a markedly high permeability, even at depths of several kilometers immediately after the formation of the fractures. We also found that the hydrothermal systems have different spatial variations and anisotropies depending on the CT numbers of the vein‐filling minerals. Our results indicate that there may be differences in the mechanisms of high‐ and low‐temperature hydrothermal circulation in oceanic crust.
Key Points
A new method has been developed to automatically detect vein characteristics from X‐ray Computed Tomography (CT) images of drilled cores
The permeability structure of the crustal section of the Samail ophiolite was estimated from the downhole profiles of detected veins
Permeability structures of High‐CT and Low‐CT vein systems have different spatial variations and anisotropies
Dissociation of quarkonium in quark–gluon plasma (QGP) is a long standing topic in relativistic heavy-ion collisions because it has been believed to signal one of the fundamental natures of the QGP — ...Debye screening due to the liberation of color degrees of freedom. Among recent new theoretical developments is the application of open quantum system framework to quarkonium in the QGP. Open system approach enables us to describe how dynamical as well as static properties of QGP influences the time evolution of quarkonium in a coherent way.
Currently, there are several master equations for quarkonium corresponding to various scale assumptions, each derived in different theoretical frameworks. In this review, all of the existing master equations are systematically rederived as Lindblad equations in a unified framework. Also, as one of the most relevant descriptions in relativistic heavy-ion collisions, quantum Brownian motion of heavy quark pair in the QGP is studied in detail. The quantum Brownian motion is parametrized by a few fundamental quantities of QGP such as real and imaginary parts of heavy quark potential (complex potential), heavy quark momentum diffusion constant, and thermal dipole self-energy constant, which constitute in-medium self-energy of a static quarkonium. This indicates that the yields of quarkonia such as J/ψ and Υ in the relativistic heavy-ion collisions have the potential to determine these fundamental quantities.
Between 2003 and 2007, 99 knees in 77 patients underwent opening wedge high tibial osteotomy. We evaluated the effect of initial stable fixation combined with an artificial bone substitute on the ...mid- to long-term outcome after medial opening-wedge high tibial osteotomy (HTO) for medial compartmental osteoarthritis or spontaneous osteonecrosis of the knee in 78 knees in 64 patients available for review at a minimum of five years (mean age 68 years; 49 to 82). The mean follow-up was 6.5 years (5 to 10). The mean Knee Society knee score and function score improved from 49.6 (SD 11.4, 26 to 72) and 56.6 (SD 15.6, 5 to 100) before surgery to 88.1 (SD 12.5, 14 to 100) and 89.4 (SD 15.6, 5 to 100) at final follow-up (p < 0.001) respectively. There were no significant differences between patients aged ≥ 70 and < 70 years. The mean standing femorotibial angle was corrected significantly from 181.7° (SD 2.7°, 175° to 185°) pre-operatively to 169.7° (SD 2.4°, 164° to 175°) at one year's follow-up (p < 0.001) and 169.6° (SD 3.0°, 157° to 179°) at the final follow-up (p = 0.69 vs one year). Opening-wedge HTO using a stable plate fixation system combined with a bone substitute is a reliable procedure that provides excellent results. Although this treatment might seem challenging for older patients, our results strongly suggest that the results are equally good.
Purpose
To assess which tibial slope measurements on knee, whole leg radiographs and three-dimensional reconstructed computed tomography (CT) were useful in clinical practice before and after opening ...wedge high tibial osteotomy.
Methods
Medial and lateral tibial slopes on knee, whole leg radiographs and three-dimensional reconstructed CT were measured in 50 patients with knee osteoarthritis. To investigate the intraobserver reproducibility and interobserver reliability for each medial and lateral tibial slope on knee, whole leg radiographs and CT, the measurements were repeated twice by two observers. The statistical differences between the medial and lateral tibial slopes obtained by the three methods, and the differences and correlation coefficients for the medial and lateral tibial slopes between knee or whole leg radiographs and CT were calculated.
Results
The reproducibility and reliability of medial and lateral tibial slopes on CT were superior to those on whole leg or knee radiographs. The medial and lateral tibial slopes on whole leg radiographs had better reproducibility and reliability than those on knee radiographs. The mean medial tibial slopes on knee, whole leg radiographs and CT were 9.3 ± 3.4°, 12.3 ± 4.3° and 11.0 ± 3.9°, respectively. The mean lateral tibial slopes were 7.9 ± 3.1°, 9.6 ± 3.6° and 9.3 ± 2.9°, respectively. The medial tibial slopes on knee, whole leg radiographs and CT were significantly higher than the lateral tibial slopes (
p
< 0.01 for all).
Conclusions
Tibial slope measurements using CT required time and specialized software. Therefore, measurements of the medial tibial slope using the long tibial axis on whole leg radiographs were more reproducible and reliable and could be an alternative to CT in clinical practice.
Level of evidence
III.
Purpose
To assess potentially predictive factors that were evaluated 1 year after the onset of symptoms in patients with spontaneous osteonecrosis of the knee (SONK) and to determine receiver ...operating characteristic (ROC) curve cut-off values.
Methods
Within 1 year of symptom onset, patients with SONK-selected treatment options, mainly based on severity of pain, chose either conservative treatment (
n
= 27 knees) or operative treatment (
n
= 27 knees). Knee and whole-leg radiographs, knee MRIs and bone mineral density scans of the lumbar spine, femoral neck and femoral condyles were obtained. The parameters measured were: (1) anatomical angle on whole-leg radiograph and (2) lesion size and medial meniscus extrusion on MRI.
Results
The anatomical angle and lesion size in the sagittal section (depth) on MRI were markedly larger in the operative treatment group than those in the conservative treatment group. The anatomical angle and depth on MRI of SONK at Stages 1–3 were significantly different between groups, with odds ratios (95 % confidence intervals) of 1.16 (1.18–2.34) and 1.11 (1.01–1.23). One year after symptom onset, ROC curve cut-off value for anatomical angle was 180° and depth on MRI was 20 mm.
Conclusion
An anatomical angle >180° and depth >20 mm on MRI were predictive factors for a poorer prognosis 1 year after symptom onset in patients with SONK. Our results on radiographs and MRI provided a predictive prognosis for patients with SONK at the initial visit to their orthopaedic surgeons.
Level of evidence
III.
An optical two-tone signal with 60 GHz frequency spacing is experimentally demonstrated, by sinusoidally modulating two lightwaves with different modulation indices and RF phases. By superposing two ...modulation lightwaves with orthogonal polarisation, polarisation orthogonality is achieved between undesired low-order optical sidebands and the desired high-order optical sidebands together with the incident light-wave. This enables us to suppress the undesired sidebands using polarisers instead of optical filter. Such operation has been implemented using optical modulator possessing RF ports for external termination, which is nested in one mode of polarisation-maintaining Sagnac interferometer (PMSI). This implementation is equivalent to optical single-sideband modulator, but required nested Mach–Zehnder structure is just one. Owing to this reduction together with use of one mode in PMSI, long-term stable operation more than 6 h has been successfully obtained, with 29 dB suppression ratio of undesired first-order sidebands against desired third-order optical sidebands.
Purpose
The correction angle after high tibial osteotomy (HTO) depends on an accurate preoperative planning and an accurate intraoperative technique. We hypothesized that the use of a navigation ...system in opening wedge HTO would improve the intraoperative target angles in the coronal and sagittal planes.
Methods
Postoperative femoro-tibial angle (FTA) and tibial posterior slope (TPS) in 28 knees with navigated opening wedge HTO were compared to those in 31 knees with the conventional method. Intraoperative correction angle was determined by the predicted medial opening width in the conventional group, and by the change of hip-knee-ankle angle in the navigated group. We defined lateral unstable knee as the knees with lateral cortex breakage or lateral tibial plateau fracture.
Results
Mean postoperative FTA was higher in the conventional group than in the navigated group (
P
< 0.037). In the conventional group, 4 lateral unstable knees were corrected to 174.6°. In the navigated group, 5 lateral unstable knees were corrected to 170.3° and no knees showed FTA > 173°. Mean change in TPS was greater in the conventional group than in the navigated group (
P
= 0.001).
Conclusion
The navigation system in opening wedge HTO might reduce undercorrection in the knees with lateral cortex breakage or lateral tibial plateau fracture, and provide the better intraoperative FTA and TPS.
Level of evidence
III.
The reason why the osteotomy line in the sagittal view should be parallel to the medial tibial posterior slope in open wedge high tibial osteotomy (OWHTO) remains unclear. In addition, previous study ...reported that a posterolateral hinge position led to an increase in tibial posterior slope (TPS) after OWHTO. Our aims were to examine the relationships between angles among the tibial plateau and osteotomy planes or the hinge point and the change in TPS, and the location of the hinge position after OWHTO using three-dimensional computed tomography (3DCT). We hypothesized that the sagittal angle between the tibial plateau and osteotomy planes with an anterior-widening proximal tibial fragment resulted in increased TPS, and the hinge position located posterolaterally.
Preoperative planning anticipated a weight-bearing line ratio of 62% on the radiograph. The anterior gap was 67% of the posterior gap in OWHTO. We identified the tibial plateau and upper and lower osteotomy planes on 3DCT of 82 patients with symptomatic medial osteoarthritic knee after OWHTO. The osteotomy plane angles between the tibial plateau and upper osteotomy planes, and opening gap angles between both osteotomy planes in the coronal and sagittal views were measured. The anteroposterior (AP) and lateral hinge position was displayed as a percentage on the upper osteotomy plane. We assessed the relationships among them.
The TPS significantly increased after OWHTO (p = 0.002). There was no significant difference between the sagittal osteotomy plane angle and the change in TPS. The sagittal opening gap angle and the AP hinge position ratio were significantly correlated with the change in the TPS (r = 0.477 p < 0.001 and r = - 0.342, p = 0.002, respectively). The hinge position was located a mean of 16.0% from the lateral and 48.6% from the posterior tibial edge in the upper osteotomy plane.
Contrary to our expectation, the osteotomy plane did not need to be parallel to the tibial plateau plane in the sagittal view. However, the osteotomy gap should be rectangular in the sagittal view. The hinge position located nearly in the center of the sagittal view.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Geophysical properties of oceanic crust are strongly influenced by the presence of cracks. We studied the effects of cracks on the physical properties of oceanic crustal rocks collected from the ICDP ...Oman Drilling Project Hole GT3A. Electrical resistivity and P‐ and S‐wave velocities were measured under dry and brine‐water‐saturated conditions for each sample. The experimental results reveal that electrical resistivity and elastic wave velocities are differently correlated with porosity. We performed joint inversion of the measured electrical and elastic properties combining an effective medium model by Kachanov and a statistical crack fluid flow model by Guéguen and Dienes with percolation theory. As a result, the variations in electrical and elastic properties can be related to the crack microstructural parameters: crack density and aspect ratio, as well as connectivity of cracks evaluated from crack density. To understand the influence of in situ conditions of oceanic crust, the joint inversion using the proposed cross‐property relationship was performed for geophysical properties obtained by logging measurements at IODP Hole 1256D. Results show the depth variations of resistivity and sonic velocities can be successfully interpreted by decreasing crack porosity and connectivity. Our data and analysis can provide new insights into the interpretation of geophysical data from the oceanic crust at which pore‐fluid plays key roles in various geodynamic activities.
Plain Language Summary
Cracks in the oceanic crust play key roles in subsurface processes, including fluid transportation, heat and chemical exchange, and microbial activity. Therefore, it is important to understand how cracks are distributed in the oceanic crust. Given that cracks exert an important influence on the physical properties of rocks, electrical and seismological surveys have been conducted at various locations in the oceanic plates. However, to quantitatively interpret the geophysical data obtained from these surveys, laboratory investigations are essential. In this study, we measured the electrical resistivity and elastic wave velocity of oceanic crustal rocks collected from drillcores of the Oman ophiolite, in which tectonic fragments of ancient oceanic plate are preserved on land. Our experimental data show that electrical resistivity and elastic wave velocity are differently correlated with porosity. Analysis of these data indicates that the variations in the electrical and elastic properties can be related to crack density, aspect ratio, and crack connectivity. The cross‐property relationship established is applied successfully to in situ geophysical data obtained by borehole logging in oceanic crust. Our data and proposed cross‐property relationship provide new insights into the interpretation of geophysical data from the oceanic crust.
Key Points
We measured the electrical resistivity and elastic wave velocity of the sheeted dike–gabbro transition zone of the Oman Drilling Project
Variation in the electrical and elastic properties of Hole GT3A was interpreted by combining effective medium model and percolation model
Applying the cross‐property relationship to logging data at IODP Hole 1256D, we estimated the crack parameters of in situ oceanic crust
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