Decrease In Vp Research Articles

4D time lapse tomography for monitoring cave propagation and stress distribution in Deep Mill Level Zone (DMLZ) PT Freeport Indonesia

Caving activity results in an increased induced seismicity which should be monitored to avoid massive and uncontrolled rock damage. This research was conducted at the Deep Mill Level Zone (DMLZ) underground mine, the deepest underground mine in Indonesia operated by PT Freeport Indonesia. This research aims to monitor cave propagation by using 4D tomography with a catalogue of microseismic for 57 days with a total of 14,821 events recorded by 84 stations consisting of 176,265 P phases and 133,472 S phases. The data is divided into four subsets to see the velocity evolution related to cave progress. Checkerboard Resolution Test (CRT) and Derivative Weight Sum (DWS) are used to assess the resolution of the inversion. 3D initial velocity model is constructed based on geological information and coring data. We have succeeded in identifying the interpreted cave propagation of a 60 m extension to the NW at around 100 m above undercut level based on 4D changes in velocity tomogram validate by Time Domain Reflectometry data. The decrease of Vp and Vs in subset 3 is interpreted due to the fracturing processes as the cave progresses. Furthermore, we observe a stress redistribution along with the progress of the cave, which is characterized by high velocities (Vp and Vs) due to compensation for changes in low velocity values ​​in the area in front of the cave, which is starting to collapse. We suggest that a considerable change in the velocity tomogram as an indicator of impending caving.

Seismic characterisation of multiple BSRs in the Eastern Black Sea Basin

Long offset seismic reflection data reveal the presence of four Bottom Simulating Reflectors (BSR0-3) within folded sediments of the Tuapse Trough, along the NE margin of the Eastern Black Sea Basin (EBSB). Multiple BSRs are observed in other sites worldwide, however, their origin and formation mechanisms are still debated. Here, we investigate the formation mechanisms of the EBSB multiple BSRs based on their seismic character and on their physical properties derived from reflected and refracted arrival seismic velocities. Seismic reflection data are downward continued to enhance refracted arrivals. A 2D travel-time velocity model of the sub-seabed, using combined travel-times from non-downward-continued reflected and downward-continued refracted signals, shows variations in the physical properties at the BSRs and nearby sediments. The P-wave velocity (VP) increase of 1.55–1.72 km/s between the seafloor and BSR0 (258 mbsf) reflects normal compaction trends in sediments, whereas the VP of 1.75–1.83 km/s between BSR0 and BSR1 (360 mbsf) is higher than that expected for sediments at that depth. Beneath BSR1, a VP decrease from 1.83 km/s to 1.61 km/s occurs within a 70-80 m-thick layer including BSR2 (395 mbsf) and extending to BSR3 (438 mbsf). Beneath BSR3, VP increases. Based on an analytical model linking seismic velocity to physical properties, these VP trends can be explained by a gas hydrate saturation from 0 to 2% between the seafloor and BSR0, reaching 4 ± 2% just above BSR1. A free gas saturation of up to 20–25% is estimated within the low-velocity zone between BSR1 and BSR3. BSR1 likely represents the present-day base of the gas hydrate stability zone (BGHSZ), which aligns with the theoretical BGHSZ assuming a geothermal gradient of 26–30 °C/km. Based on seismic polarities and results from travel-time analysis and rock physics modelling, we suggest that hydrate dissociation and recycling processes may explain the negative polarity of BSR2 and BSR3, which are still visible due to the presence of relict gas, and inferred higher gas hydrate saturations close to the present-day base of the stability zone at BSR1. Also, structural and stratigraphic controls seem to have favoured focused free gas flow and hydrate formation at the top of an anticlinal structure, thus likely controlling multiple BSR generation in the EBSB.

Effects of partial saturation on the liquefaction resistance of sand and silty sand from Christchurch

The liquefaction resistance of partially saturated soil was experimentally investigated for one clean sand and one silty sand collected from a site in Christchurch, in an area severely affected by liquefaction in the 2010–2011 Canterbury earthquakes. A series of cyclic undrained tests were performed on fully and partially saturated sand and silty sand specimens, in conjunction with evaluation of saturation conditions in situ based on comprehensive field measurements of P-wave velocity (Vp) in Christchurch deposits. The Skempton’s B-value and P-wave velocity were comparatively used as measures for partial saturation in the laboratory. B-value - Vp relationships from the test results indicate that Vp steadily increases with the B-value until a threshold B-value is reached beyond which Vp remains unchanged at values indicating full saturation, i.e. Vp ;≥ ;1600 ;m/s. In general, the liquefaction resistance of tested sand and silty sand increases with a decrease in the B-value or Vp, i.e. with a reduction in the degree of saturation. Furthermore, test results suggest existence of threshold B-values and Vp for tested soils beyond which no significant increase in the liquefaction resistance was observed. This threshold B-values and Vp were found to be dependent on soil type and applied confining stress. The effects of partial saturation on liquefaction strength are different for the sand and silty sand when using Vp as a measure for the degree of saturation. While a gradual rate of increase in liquefaction strength with decreasing Vp is observed for the tested sand, the liquefaction strength of silty sand shows similar gradual increase with a decrease in Vp up to about 800 ;m/s, which is then followed by an abrupt increase in the liquefaction strength for Vp ;< ;800 ;m/s. Generally good agreement between liquefaction strength of tested soils and published data was observed, with a clear distinctive feature in the behaviour of the silty sand as compared to clean sands.

Evolution law of ultrasonic characteristics and its relationship with coal-measure sandstone mechanical properties during saturation and desaturation

Underground buildings are easily destabilised by water and there is a strong link between their mechanical properties and ultrasonic characteristics. To grasp the above features and the relationship among them, the mechanism of sandstone degradation under water erosion was briefly reviewed. Using the coal-measure sandstone as the object, experimental studies on the dynamic evolution of water content, ultrasonic wave velocity, waveform, uniaxial compressive strength (UCS), elastic modulus (E), and damage mode during saturation-desaturation were carried out. The findings demonstrate that coal-measure sandstones usually exhibit more mechanical parameter deterioration following saturation than non-coal-measure sandstones. During saturation, the water absorption velocity slows down; the P-wave velocity (VP) first fluctuates down, then fluctuates up and finally decreases slightly (VP increases after saturation), and the wave velocity anisotropy coefficient (δi) decreases; the waveform shows a trend of unequal time and unequal amplitude → equal time and equal amplitude → unequal time and equal amplitude, and the first wave reaches a progressively shorter time. During desaturation, the dehydration rate slows down, VP first drops rapidly and then fluctuates slightly and rises slightly near drying (VP decreases after desaturation), δi increases, and the waveform changes in the opposite trend to saturation. Saturation treatment significantly weakened the mechanical properties, while desaturation restored some of the strength lost due to immersion. The sandstone mechanical properties and ultrasonic features are more closely related during saturation than desaturation.

Non-Destructive Evaluation of Mortar with Ground Granulated Blast Furnace Slag Blended Cement Using Ultrasonic Pulse Velocity.

Non-destructive evaluation using ultrasonic pulse velocity (Vp) testing has extensive applications in the concrete industry. With advances in construction technology, the use of ground granulated blast furnace slag (GGBFS) as a partial replacement to cement in a concrete mix is growing in popularity primarily because it reduces the initial capital cost of raw materials and the associated energy costs. This paper investigates the effect of the water-to-cement (wc) ratio and the cement content replaced by GGBFS on the development with time of the ultimate compressive strength () and the compression wave velocity (Vp) of mortar. The results showed that in the case of mortar with higher percentages of GGBFS replacement (where nucleation surfaces are more abundant), increasing wc can increase but cause a decrease in Vp. The posterior hydration process is highly dependent upon the water particles in the mixture after the first stage of hydration. After 7 days of curing, experimental results show that the of slag blended cement mix design wc ratio of 0.6 surpassed the value of an Ordinary Portland cement. A regression model correlating the and Vp of slag blended mortar is developed, which can be used to predict at concrete ages ranging from 1 day to 28 days for mixes with GGBFS percentage replacement values ranging from 15% to 45%.

Investigation of dendrite growth, Nb segregation during laser IN718 deposition via volume of fluid-phase field modeling

In this work, a macro-micro VOF-PF (Volume of Fluid-Phase field) model is established to simulate the heat transfer, dendrite growth and Nb segregation during the laser IN718 deposition. According to calculated heat transfers, G increases, while Vp decreases, and the corresponding G×Vp decreases from top to bottom in the molten pool. The calculated the primary dendrite arm spacing (PDAS) using the PF model increases from top to bottom. Compared with other models, the calculated PDAS using the PF model considering the liquid-metal flow is closest to experiment measurements. During the dendrite growth, Nb is enriched in the interdendritic region, and finally is distributed in the droplet shape. The calculated actual solute distribution coefficient Cmin/Cmax decreases from 0.584 to 5.548 with the decrease of G×Vp, which follows the equilibrium solidification theory. According to dc/dy=G/ml, the liquidus slope ml is calculated as 0.05322wt.%/μm very close to the theoretical value 0.05394wt.%/μm. The simulated Nb concentrations in the matrix γ and Laves phases are 3.97wt.%, 13.3wt.% respectively, which are in good agreements with experimental 3.7wt.% and 13wt.%.

Effect of temperature on elastic properties of biotite and biotite-rich rocks: estimation from experiment and molecular dynamics simulation

SUMMARY We measured the P-wave velocities (VP) of mafic high-grade metamorphic rocks at 1.0 GPa pressure and a range of temperatures from 25 to 400 °C, along orthogonal directions corresponding to macroscopic fabric elements in the specimen. Our results showed that biotite-rich rocks (over 15 vol per cent biotite) displayed a strong decrease in VP with increasing temperature whereas biotite-free rocks did not. The anisotropy of VP (AVP) in biotite-rich rocks also increased with increasing temperature because of differential VP reduction, indicating a thermal dependence of the elastic properties of biotite. We conducted molecular dynamics simulations to investigate the effect of temperature on the elastic stiffness constants (Cij) of phlogopite, an end member of the biotite solid-solution series. The simulations indicated that Cij of phlogopite have a strong anisotropy and temperature dependence. We then estimated Cij of the bulk rock by using the Voigt–Reuss–Hill average procedure based on the estimated Cij of phlogopite, reference values for Cij of hornblende and plagioclase and measured crystal preferred orientations. From the resulting values of bulk-rock Cij, we calculated the quasi-VP and anisotropy parameter ε, under the assumption of transverse isotropy, and confirmed that temperature had a clear effect on velocity whereas AVP remained stable. This result suggests that the thermal effect on VP of biotite-rich rocks can be explained by the thermal dependence of Cij of phlogopite, which we attribute to a lattice rearrangement in phlogopite. This finding implies that the elastic properties of micas may change and affect the elastic properties of bulk rocks in the absence of mechanical breakage, dehydration reactions or phase changes. The thermal effect on AVP of biotite-rich rocks cannot be explained by a thermal dependency of the elastic constants of phlogopite. We speculate that the local concentration of thermal stress on biotite may account for the thermal dependency of AVP of biotite-rich rocks.

Value of troponin T as a screening test of cardiac structure and function in chronic kidney disease

Background: Cardiovascular disease starts early in the course of chronic kidney disease (CKD) and is the leading cause of death in patients with end-stage renal disease. Since high-sensitivity cardiac troponin T (hs-cTnT) can detect much lower levels of myocardial injury than conventional assays, it may be useful for studying the earliest stages of heart disease in patients with CKD.Objective: To evaluate the association of circulating hs-cTnT with LV structural and functional abnormalities detected by echocardiography among dialysis dependent and non-dialysis dependent CKD patients.Methods: This study was conducted on 107 subjects divided into three groups.Group I consisted of CKD patients on conservative treatment (n=42), Group II: hemodialysis patients (n=42), Group III: control group: age and sex matched healthy volunteers (n=23). All subjects were subjected to clinical examination, biochemical evaluation including estimation of hs-cTnT and Echo-Doppler study of cardiac structure and function.Results: There was a significant increase in LAV (p&lt;0.01), LVM (p&lt;0.01) in both patient groups compared to the control group. Mitral annular plane systolic excursion (MAPSE) was significantly decreased in both patient groups compared to the control group (p&lt;0.01, p&lt;0.05) and in group I compared to group II (p&lt;0.05) with a significant decrease in S velocity in group I compared to groups II and III (p&lt;0.01). There was a significant decrease in Vp (p&lt;0.01) with a significant increase in AEF (p&lt;0.01) in both patients’ groups compared to the control group and AEF was significantly increased in group II compared to group I (p&lt;0.01). Ea velocity and Ea/Aa decreased significantly (p&lt;0.01) with significant increase in Aa velocity (p&lt;0.05, p&lt;0.01), E/Ea (p&lt;0.01) and E/Vp (p&lt;0.05) in both patient groups compared to the control group. There was a significant increase in hs-cTnT levels in both patient groups compared to the control group (P&lt;0.01). We found a positive correlation between hs-cTnT levels and LAV (r=0.291, p&lt;0.03), IVST (r=0.374, p&lt;0.004), PWT (r=0.309, p&lt;0.02), LVM (r=0.282, p&lt;0.03), A wave velocity (r=0.271, p&lt;0.04), E/Ea (r=0.506, p&lt;0.0001), PCWP (r=.507, p&lt; 0.0001) and a negative correlation between hs-cTnT and MAPSE (r=-0.300, p&lt;0.02), S wave velocity (r= -0.259, p&lt;0.05), Ea (r=-626, p&lt;0.0001), Ea/Aa (r=-0.543, p&lt;0.0001). Troponin at the cut-off value of &gt;5 ng/L, revealed 100% sensitivity and 95% specificity with areas under curve (AUC) of 0.998 and accuracy of 95.65% (P&lt;0.01) for discrimination of Group I vs control group and 76.2% sensitivity and 95.7% specificity with AUC 0.796 and accuracy 71.84% (P&lt;0.01) for discrimination of group II vs control group. Conclusion: Structural and functional cardiac abnormalities are common in CKD patients. Serum hs-cTnT levels increased in CKD patients and was associated with LVH, LAV and some of the echocardiographic parameters of LV systolic and diastolic dysfunction. Our research suggests that hs-cTnT levels may be important for early screening of cardiac structure and function in CKD patients to provide evidence for early intervention.

Value of troponin T as a screening test of cardiac structure and function in chronic kidney disease.

Background: Cardiovascular disease starts early in the course of chronic kidney disease (CKD) and is the leading cause of death in patients with end-stage renal disease. Since high-sensitivity cardiac troponin T (hs-cTnT) can detect much lower levels of myocardial injury than conventional assays, it may be useful for studying the earliest stages of heart disease in patients with CKD.Objective: To evaluate the association of circulating hs-cTnT with LV structural and functional abnormalities detected by echocardiography among dialysis dependent and non-dialysis dependent CKD patients.Methods: This study was conducted on 107 subjects divided into three groups.Group I consisted of CKD patients on conservative treatment (n = 42), Group II: hemodialysis patients (n = 42), Group III: control group: age and sex matched healthy volunteers (n = 23). All subjects were subjected to clinical examination, biochemical evaluation including estimation of hs-cTnT and Echo-Doppler study of cardiac structure and function.Results: There was a significant increase in LAV (p < 0.01), LVM (p < 0.01) in both patient groups compared to the control group. Mitral annular plane systolic excursion (MAPSE) was significantly decreased in both patient groups compared to the control group (p < 0.01, p < 0.05) and in group I compared to group II (p < 0.05) with a significant decrease in S velocity in group I compared to groups II and III (p < 0.01). There was a significant decrease in Vp (p < 0.01) with a significant increase in AEF (p < 0.01) in both patients’ groups compared to the control group and AEF was significantly increased in group II compared to group I (p < 0.01). Ea velocity and Ea/Aa decreased significantly (p < 0.01) with significant increase in Aa velocity (p < 0.05, p < 0.01), E/Ea (p < 0.01) and E/Vp (p < 0.05) in both patient groups compared to the control group.There was a significant increase in hs-cTnT levels in both patient groups compared to the control group (P < 0.01). We found a positive correlation between hs-cTnT levels and LAV (r = 0.291, p < 0.03), IVST (r = 0.374, p < 0.004), PWT (r = 0.309, p < 0.02), LVM (r = 0.282, p < 0.03), A wave velocity (r = 0.271, p < 0.04), E/Ea (r = 0.506, p < 0.0001), PCWP (r = .507, p < 0.0001) and a negative correlation between hs-cTnT and MAPSE (r = − 0.300, p < 0.02), S wave velocity (r = − 0.259, p < 0.05), Ea (r = − 626, p < 0.0001), Ea/Aa (r = − 0.543, p < 0.0001).Troponin at the cut-off value of >5 ng/L, revealed 100% sensitivity and 95% specificity with areas under curve (AUC) of 0.998 and accuracy of 95.65% (P < 0.01) for discrimination of Group I vs control group and 76.2% sensitivity and 95.7% specificity with AUC 0.796 and accuracy 71.84% (P < 0.01) for discrimination of group II vs control group.Conclusion: Structural and functional cardiac abnormalities are common in CKD patients. Serum hs-cTnT levels increased in CKD patients and was associated with LVH, LAV and some of the echocardiographic parameters of LV systolic and diastolic dysfunction.Our research suggests that hs-cTnT levels may be important for early screening of cardiac structure and function in CKD patients to provide evidence for early intervention.

Stress wave transmission and frequency-domain responses of gap-graded cohesionless soils

Gap-graded cohesionless soils are extensively utilized in numerous man-made geotechnical structures such as earthen embankments, man-made fills and used for the prevention of seepage in dams and tailings of mines. However, there is a lack of research available on investigating the transitional behaviour of frequency responses of gap-graded cohesionless soils. Therefore, the present research explores the stress wave transmission in gap-graded silica sand mixtures (having median particle size ratio of 6.4) using disk-shaped piezoelectric transducers (DTs). By employing DTs, shear (Vs) and compression (Vp) wave velocities are measured using more planar waves and eliminate the possibility of fine particle segregation commonly encountered during insertion of bender elements. The experimental results indicate that at an equivalent void ratio, Vs and Vp decrease initially with the increase in fine silica sand content (Fs); however, once a transitional value (Fs,thr) is attained, Vs and Vp start to rise and move towards the values for fine silica sand. Such transitional behaviours of elastic wave velocities and frequency-domain responses are dependent on the state of packing, i.e. denser specimens achieve this at a lower Fs than the looser equivalents. It is observed that for a given Fs, there exists a linear relationship between the maximum transmitted frequency in the packing, i.e. low-pass frequency (flp) and the Vs. Furthermore, a novel approach has been described by which the type of gap-graded mixture, i.e. underfilled (internally unstable) or overfilled (stable), can be assessed by experimentalists from the slope of flp–Vsresponses. The advantage of adopting flp to categorize the gap-graded mixtures is that the same is more sensitive to Fs in comparison to Vs or Vp, and thus a more robust analysis can be achieved.

Study on the surface crack propagation mechanism of coal and sandstone subjected to cryogenic cooling with liquid nitrogen

Conventional hydraulic fracturing often causes problems such as reservoir damage, water consumption, and pollution. Recently, liquid nitrogen (LN2) fracturing, an environmentally friendly fracturing technology, has attracted more attention. In this paper, the mechanism of surface crack propagation in coal and sandstone induced by LN2 is explored through laboratory tests and numerical simulations. An ultrasound detection analyser is employed to investigate the longitudinal wave velocity (Vp) changes in specimens before and after LN2 cooling. The micromorphology of specimens is observed through scanning electron microscopy (SEM). Furthermore, the heat transfer characteristics and damage zone of specimens induced by LN2 are determined. The experimental results indicate that LN2 cooling is more effective for improving coal permeability than it is for improving sandstone permeability. After LN2 cooling, a complex fracture network is observed from the coal surface. However, limited damage to the sandstone surface is observed. Vp decreases by 24.7%–38.1% for coal specimens after cooling but by less than 0.06% for sandstone. The simulation results indicate that the low-temperature region and the tensile area gradually expand into the interior of the specimens with time. However, the temperature of sandstone drops faster than coal when specimens contact LN2. The maximum tensile stress induced by the instantaneous contact between the specimens and LN2 can be generated at the outer surface of the specimens. Moreover, the maximum damage area of coal extends 3.3 mm from the outer surface, while the damage zone of the sandstone is almost zero.

Ferric iron in bridgmanite and implications for ULVZs

The seismic velocities of ferric iron-enriched bridgmanite under core-mantle boundary (CMB) conditions were calculated using GGA + U ab initio molecular dynamics to probe whether ferric iron enriched mantle can explain the properties of ultra-low velocity zones (ULVZ). Under these conditions ferric iron demonstrated some unusual properties.The effect of ferric iron on the 0 K transition pressure of the bridgmanite (bdg) to postperovskite (ppv) transition with GGA + U has some dependence upon the value of Ueff that is set for B site ferric iron which is in contrast to most substances where Ueff has little effect on the properties. We find that ferric iron can both stabilise and destabilise the bdg phase relative to the ppv phase depending upon the value of Ueff. This is due to the spin state transition of B-site ferric iron and was not seen in ferrous or aluminous ferric bridgmanite which lack such a transition at mantle conditions. Due to the similar energies and pressure derivatives of the bdg and ppv phases very subtle energy changes (such as that of iron clustering or different theoretical or experimental setups) can have large effects on the relative phase stabilities at different pressures.The spin state of ferric iron in bdg demonstrates some novel behaviours. With large iron enrichment the spin state of the B site has a non-linear dependence on concentration and depends upon the local arrangement of iron. At typical lower mantle pressures, ferric iron is expected to be high spin in the A site and low spin at the B site but at the temperatures of the CMB thermal spreading of the electrons causes ferric iron at the B site to become high spin.This is not a typical “spin transition” however as it involves no structural rearrangement of the unit cell and is predicted to have no effect on the elasticity and thus the seismicity of the crystal.Our elasticity results show that at the CMB ferric iron-enriched bridgmanite has nearly identical Vp and Vs to ferrous iron-bearing bridgmanite, and thus bridgmanite containing large amounts of Fe2+ or Fe3+ can both explain ULVZ properties when mixed with ferropericlase. We find, however, that mixing of both ferric and ferrous iron in bridgmanite causes a large (up to 1 km/s) non-ideal decrease in Vp when there is middling amounts of ferric iron. This non-linear mixing should have significant effects throughout the lower mantle whenever such amounts of ferric iron are present though such a ferrous:ferric ratio would typically require an increase of the natural ferrous:ferric ratio (for example through very high oxidation fugacities or chemical doping). In the case of ULVZs this non-linear mixing significantly impairs the fitting to some ULVZ data sets (those with a dlnVs/dlnVp ~ 3), but greatly improves the fitting to other ULVZ data sets (those with a dlnVs/dlnVp ~ 1).The oxidation state of highly enriched iron in bridgmanite at CMB conditions has, therefore, a large effect on the ability of mantle mixtures that are highly enriched in iron to replicate ULVZ properties.

The Effects of Shear Strain, Fabric, and Porosity Evolution on Elastic and Mechanical Properties of Clay‐Rich Fault Gouge

AbstractThe elastic and mechanical properties of fault gouge are key controls on fault zone stiffness, strength, damage, healing, and sliding stability. Clay minerals are prevalent in fault zones and have significant effects on friction, porosity, elastic properties, and shear fabric development. Although clay‐rich gouges are well studied, the roles of porosity evolution and fabric formation in modulating elastic and mechanical properties are unclear. We have found that with progressive shear, the role of strain localization and fabric development may compete with densification to control the evolution of friction and elastic moduli. We report on a suite of double‐direct shear experiments on synthetic gouge composed of 50% Ca‐montmorillonite and 50% granular quartz at a normal stress of 25 MPa. We measure the coefficient of friction, porosity, P and S wave speeds, and bulk and shear moduli, and their evolution with shearing, to shear strains up to ~25. We find that the evolution of Vp, Vs, and elastic moduli are controlled by the interplay of porosity loss, shear fabric development, and particle contact stiffness. In general, Vp, Vs, and elastic moduli increase with shear strain and are accompanied by gradual densification and porosity loss. However, at intermediate shear strains (~2–8) a decrease in Vp, Vs, and elastic moduli is superimposed on this overall trend. Based on previous microstructural studies, we hypothesize that fabrics develop parallel to shear direction (perpendicular to wave propagation) over this range of strains, leading to reduced fault stiffness and competing with porosity loss as the dominant control on elastic properties.

Modulation of electron energy distribution functions and plasma parameters in a dual-frequency cylindrical ICP source

In this paper, a new dual-frequency cylindrical inductively coupled plasma source which operates with dual-frequencies (high-frequency (HF) 13.56 MHz and low-frequency (LF) 2 MHz) and dual-antennas (a 2-turn HF antenna and a 6-turn LF antenna) is designed, and the effects on electron energy distribution function and plasma parameters (i.e., plasma density ne, electron temperature Te, plasma floating potential Vf and plasma potential Vp) in the following cases are investigated: (1) fixed HF power of 500 W and LF power varying from 300 W to 900 W, (2) fixed LF power of 500 W and HF power varying from 300 W to 900 W. It is found that increasing HF power enhances the population of high-energy electrons, while increasing LF power increases the population of low-energy electrons. This result can be explained by the different electron heating mechanisms, i.e., ohmic heating for the LF discharge and collisional-less heating for the HF discharge at an argon gas pressure of 15 mTorr. Moreover, the different influences of HF power on ne, Te, Vf, Vp at fixed LF 500 W and that of LF power on ne, Te, Vf, Vp at fixed HF power 500 W are compared. It is found that although ne increases with both HF and LF power, it increases more significantly with the change of HF power. This indicates that ne is mainly determined by the HF power and slightly influenced by the LF power. Furthermore, the Te, Vf and Vp decrease with increasing LF power at a fixed HF power of 500 W, which is contrary to the trend of Te, Vf and Vp with increasing HF power at the same LF power of 500 W.

Dynamic contrast-enhanced magnetic resonance imaging of osseous spine metastasis before and 1 hour after high-dose image-guided radiation therapy.

OBJECTIVE High-dose image-guided radiation therapy (HD IGRT) has been instrumental in mitigating some limitations of conventional RT. The recent emergence of dynamic contrast-enhanced (DCE) MRI to investigate tumor physiology can be used to verify the response of human tumors to HD IGRT. The purpose of this study was to evaluate the near-immediate effects of HD IGRT on spine metastases through the use of DCE MRI perfusion studies. METHODS Six patients with spine metastases from prostate, thyroid, and renal cell carcinoma who underwent HD IGRT were studied using DCE MRI prior to and 1 hour after HD IGRT. The DCE perfusion parameters plasma volume (Vp) and vascular permeability (Ktrans) were measured to assess the near-immediate and long-term tumor response. A Mann-Whitney U-test was performed to compare significant changes (at p ≤ 0.05) in perfusion parameters before and after RT. RESULTS The authors observed a precipitous drop in Vp within 1 hour of HD IGRT, with a mean decrease of 65.2%. A significant difference was found between Vp values for before and 1 hour after RT (p ≤ 0.05). No significant change was seen in Vp (p = 0.31) and Ktrans (p = 0.1) from 1 hour after RT to the first follow-up. CONCLUSIONS The data suggest that there is an immediate effect of HD IGRT on the vascularity of spine metastases, as demonstrated by a precipitous decrease in Vp. The DCE MRI studies can detect such changes within 1 hour after RT, and findings are concordant with existing animal models.

A case study in quantitative interpretation ambiguity, lambda-mu-rho, and rock-physics modeling in the Otway Basin, Australia

A rock-physics study and AVO modeling study have been completed to assist in the interpretation of seismic amplitude and AVO anomalies in the Shipwreck Trough of the offshore Otway Basin of southeastern Australia. Elastic log data, core data (both full and sidewall), and associated thin-section analysis of composition and texture were available on several wells, and these data are important in calibrating proposed rock-physics models that suggest that incorporating cement is critical to understanding anomalies in seismic and measured log data. Lithoprobability volumes based on conventional interpretation paradigms, such as low VP/VS values indicating gas presence, that do not incorporate an understanding of rock physics lead to biased interpretations. Ratios in particular can be misleading because there is ambiguity about whether an anomalous ratio is driven by the numerator or denominator. As a classic gas indicator, low VP/VS values are interpreted to be driven by a decrease in VP associated with gas replacing brine in a rock. Using Lamé impedance terms λρ and μρ, however, provides an alternative interpretation template that does not use ratios and can improve insight into rock properties. As in this recent case study, using lambda-mu-rho (LMR) can be an important tool when shear velocity has increased relative to compressional velocity, irrespective of any pore-fluid change. In the reservoir rocks of the Shipwreck Trough, low VP/VS in both gas-saturated and brine-filled sandstone is caused by quartz cement. This presents a substantial challenge to the use of a standard rock-physics template. In LMR space, however, low VP/VS data points clearly are characterized by high shear rigidity — an important point to recognize and incorporate into AVO interpretation workflows.

Relative stability and contrasting elastic properties of serpentine polymorphs from first‐principles calculations

AbstractWe conduct first‐principles calculations to determine the relative stability field and elasticity contrast of serpentine polymorphs at pressure and temperature conditions relevant to the oceanic lithosphere and subduction zone. At high pressures (&gt;4 GPa), the corrugated form of serpentine polymorph (antigorite, Atg) plus brucite (Brc) assemblage is thermodynamically more favorable compared to its planar counterpart (lizardite, Liz). The phase boundary between Liz and Atg + Brc exhibits a negative slope in the whole P‐T range, indicating that this transition can be driven by increasing either pressure or temperature. Near 0 GPa, the slope is about −33 K/GPa. As pressure exceeds 1 GPa, the transition temperature starts to decrease more rapidly. Because of the corrugated nature of its constituent layers, Atg is more susceptible to intralayer deformations (7 to 36% smaller C11, C22, C12, and C66 at ambient conditions) while more resistant to interlayer shear deformation (25% larger C44, 36% larger C55) than Liz. In contrast, their responses to the interlayer compressive deformation (C33) are similar. For isotropic polycrystalline aggregates at pressures between 0 and 4 GPa, Atg exhibits a smaller bulk modulus (12 to 15%) and a larger shear modulus (6 to 11%) than Liz, while their density contrast is within 1%. Accordingly, a Liz/Atg transition is accompanied by a decrease in Vp (2 to 3%), an increase in Vs (3 to 5%), and a more pronounced drop in Vp/Vs (6 to 8%). These results may help to identify and characterize serpentine polymorphs produced under various geological settings.

Studying cerebral hemodynamics and metabolism using simultaneous near-infrared spectroscopy and transcranial Doppler ultrasound: a hyperventilation and caffeine study.

Caffeine is one of the most widely consumed psycho-stimulants in the world, yet little is known about its effects on brain oxygenation and metabolism. Using a double-blind, placebo-controlled, randomized cross-over study design, we combined transcranial Doppler ultrasound (TCD) and near-infrared spectroscopy (NIRS) to study caffeine's effect on middle cerebral artery peak blood flow velocity (Vp), brain tissue oxygenation (StO2), total hemoglobin (tHb), and cerebral oxygen metabolism (CMRO2) in five subjects. Hyperventilation-induced hypocapnia served as a control to verify the sensitivity of our measurements. During hypocapnia (∼16 mmHg below resting values), Vp decreased by 40.0 ± 2.4% (95% CI, P < 0.001), while StO2 and tHb decreased by 2.9 ± 0.3% and 2.6 ± 0.4%, respectively (P = 0.003 and P = 0.002, respectively). CMRO2, calculated using the Fick equation, was reduced by 29.3 ± 9% compared to the isocapnic-euoxia baseline (P < 0.001). In the pharmacological experiments, there was a significant decrease in Vp, StO2, and tHb after ingestion of 200 mg of caffeine compared with placebo. There was no significant difference in CMRO2 between caffeine and placebo. Both showed a CMRO2 decline compared to baseline showing the importance of a placebo control. In conclusion, this study showed that profound hypocapnia impairs cerebral oxidative metabolism. We provide new insight into the effects of caffeine on cerebral hemodynamics. Moreover, this study showed that multimodal NIRS/TCD is an excellent tool for studying brain hemodynamic responses to pharmacological interventions and physiological challenges.

Degradation of the mechanical properties imaged by seismic tomography during an EGS creation at The Geysers (California) and geomechanical modeling

Using coupled thermal-hydro-mechanical (THM) modeling, we evaluated new seismic tomography results associated with stimulation injection at an EGS demonstration project at the Northwest Geysers geothermal steam field, California. We studied high resolution seismic tomography images built from data recorded during three time periods: a period of two months prior to injection and during two consecutive one month periods after injection started in October 2011. Our analysis shows that seismic velocity decreases in areas of most intense induced microseismicity and this is also correlated with the spatial distribution of calculated steam pressure changes. A detailed analysis showed that shear wave velocity decreases with pressure in areas where pressure is sufficiently high to cause shear reactivation of pre-existing fractures. The analysis also indicates that cooling in a liquid zone around the injection well contributes to reduced shear wave velocity. A trend of reducing compressional wave velocity with fluid pressure was also found, but at pressures much above the pressure required for shear reactivation. We attribute the reduction in shear wave velocity to softening in the rock mass shear modulus associated with shear dislocations and associated changes in fracture surface properties. Also, as the rock mass become more fractured and more deformable this favors reservoir expansion caused by the pressure increase, and so the fracture porosity increases leading to a decrease in bulk density, a decrease in Young modulus and finally a decrease in Vp.

Temperature effect on high salinity depuration of Vibrio vulnificus and V. parahaemolyticus from the Eastern oyster (Crassostrea virginica)

Vibrio vulnificus (Vv) and Vibrio parahaemolyticus (Vp) are opportunistic human pathogens naturally associated with the Eastern oyster Crassostrea virginica. The abundances of both pathogens in oysters are positively correlated with temperature, thus ingestion of raw oysters during the warm summer months is a risk factor for contracting illness from these bacteria. Current post-harvest processing (PHP) methods for elimination of these pathogens are expensive and kill the oyster, changing their organoleptic properties and making them less appealing to some consumers. High salinity has proven effective in reducing Vv numbers in the wild and our research aims at developing an indoor recirculating system to reduce pathogenic Vibrios while maintaining the taste and texture of live oysters. The goal of this study was to determine the influence of temperature on the efficacy of high salinity depuration. Vv was enumerated as most probable number (MPN) per gram of oyster tissue using the FDA-approved modified cellobiose polymyxin colistin (mCPC) protocol and with an alternative Vibrio specific media CHROMagar™ Vibrio (CaV). CaV was also used to quantify Vp. Oysters were held at 35psu for 10days at three temperatures: low (20°C), mid (22.5°C) and high (25°C). There was no difference in MPN/g of Vv between media; however more Vv isolates were obtained from mCPC than CaV. There was no significant effect of temperature on reduction of Vv or Vp throughout depuration but there was a tendency for low temperatures to be less effective than the higher ones. High salinity resulted in a significant decrease in Vv by day 3 and again by day 10, and a decrease in Vp by day 3. Oyster condition indices were maintained throughout depuration and mortality was low (4% across three trials). Overall these results support the use of mCPC for Vv enumeration and demonstrate the promise of high salinity depuration for PHP of the Eastern oyster. The trend for lower temperatures to be less effective is surprising and indicates a potential interaction between salinity and temperature that should be further investigated.