Dependability tools are becoming an indispensable tool for modeling and analyzing (critical) systems. However the growing complexity of such systems calls for increasing sophistication of these ...tools. Dependability tools need to not only capture the complex
dynamic behavior of the system components, but they must be also easy to use, intuitive, and computationally efficient. In general, current tools have a number of shortcomings including lack of modeling power, incapacity to efficiently handle general component failure distributions, and ineffectiveness in solving large models that exhibit complex dependencies between their components. We propose a novel reliability modeling and analysis framework based on the
Bayesian network (BN) formalism. The overall approach is to investigate timed Bayesian networks and to find a suitable reliability framework for dynamic systems. We have applied our methodology to two example systems and preliminary results are promising. We have defined a discrete-time BN reliability formalism and demonstrated its capabilities from a modeling and analysis point of view. This research shows that a BN based reliability formalism is a powerful potential solution to modeling and analyzing various kinds of system components behaviors and interactions. Moreover, being based on the BN formalism, the framework is easy to use and intuitive for non-experts, and provides a basis for more advanced and useful analyses such as system diagnosis.
Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current ...understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate‐bearing sediments. Formation phenomena include pore‐scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small‐strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate‐bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate‐bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.
Adding charcoal to soil (biochar soil amendment) can sequester carbon and improve soil performance, although the extent and exact mechanisms of soil improvement are not clear. Additionally, biochar ...properties can vary significantly with production conditions. Here we characterize the impact of pyrolysis temperature on two important soil hydrologic properties: field capacity and hydrophobicity. We show that pure biochar exhibits a wide range in both properties depending on feedstock and pyrolysis conditions. We find that both properties can be controlled by choice of pyrolysis temperature; 400 °C–600 °C produced biochars with the most desirable hydrological properties (peak field capacity and minimum hydrophobicity). Further, we show that hydrophobicity is strongly correlated (R2 = 0.87; p < 0.001) to the presence of alkyl functionalities in FTIR spectra, suggesting that this property derives from aliphatic domains on the surface of low-temperature biochars. Although we could relate hydrophobicity to biochar chemistry, our chemical characterization techniques were insufficient to describe variation in field capacity of soil–biochar mixtures. Field capacity may be related to large biochar pores, suggesting the need for quantitative techniques to characterize large (greater than 0.1 μm) pores within biochar particles.
► Pyrolysis temperature and feedstock drive variation in biochar field capacity and hydrophobicity. ► Hydrologic behavior of pure biochars does not necessarily predict the behavior of biochar-amended soils. ► Optimum hydrologic properties of biochar occur at production temperatures between 400 and 600 °C, depending on feedstock. ► A full constraint of biochar hydrologic behaviors requires better tools to constrain pore size, structure, and connectivity.
We present a method to simultaneously constrain both far-field horizontal stress magnitudes (
S
hmin
and
S
Hmax
) and in situ rock unconfined compressive strength (UCS), using geophysical logging ...data from two boreholes located 70 m apart that access the uppermost accretionary prism of the Nankai subduction zone . The boreholes sample the same sediments and are affected by the same tectonic stress field, but were drilled with different annular pressures, thus providing a unique opportunity to refine estimates of both in situ stress magnitudes and rock strength. We develop a forward model to predict the angular width of compressional wellbore failures (borehole breakouts), and identify combinations of
S
Hmax
and UCS that best match breakout widths observed in resistivity images from the two boreholes. The method requires knowledge of
S
hmin
, which is defined by leak-off tests conducted during drilling. Our results define a normal to strike-slip stress regime from 900 to 1386 m below seafloor, consistent with observations from seismic and core data. Our analysis also suggests that in situ values of UCS are generally slightly lower that commonly assumed on the basis of published empirical relations between UCS and P-wave velocity.
The purpose of this report is to describe the development and implementation of a pharmacist-led naloxone-training and prescription service at a county health department.
Jefferson County Department ...of Health, Birmingham, Alabama.
This service was developed in response to the overwhelming heroin and opioid epidemic that is currently affecting the entire nation and which is highly prevalent in the state of Alabama. Because of this epidemic, new state laws have been established regarding prescriptive authority, liability, and possession of naloxone.
Through a collaborative protocol, pharmacists at the Jefferson County Department of Health were responsible for prescribing and educating the public about naloxone.
Between 2014 and 2015 the Jefferson County Coroner reported a 131% increase in opioid prescription-related deaths indicating the continued need for the naloxone prescription program.
In total, 83 clients were trained and 150 naloxone kits were distributed among heroin and opioid users, concerned family members or friends, and those who work closely with users.
This service and its extending arms were developed in response to the need for naloxone education among heroin and opioid users, their family members, civil servants who work with users, and family practice physicians who prescribe opioids.
Dissolved chloride concentrations higher than seawater were observed over a broad depth range in pore water profiles from International Ocean Discovery Program Site U1517 on the Hikurangi Margin. ...This Cl maximum is not associated with an 87Sr/86Sr anomaly, indicating that it is not caused by hydration reactions during ash alteration. We use a numerical modeling approach to examine possible causes for recent gas hydrate formation that can result in the observed Cl high. Our approach considers sedimentation, sea level, and bottom water temperature (BWT) changes due to glaciation as drivers for the downward migration of the base of gas hydrate stability and gas hydrate formation. The modeling results reveal that lowering of sea level during glaciation can allow methane hydrate dissociation followed by postglacial hydrate formation as sea level rises. However, BWT cooling of 2 °C during glaciation followed by warming during deglaciation would mostly counteract the impacts of sea level change. Bottom water cooling during glaciation is expected in this region and many locations worldwide. As a result, our simulations do not support the previous hypotheses of large‐scale gas hydrate dissociation due to sea level drop during glaciation, which have been proposed as triggers for widespread gas release and slope failure. Such a mechanism is only possible where BWT remains constant or increases during glaciation. Our simulations indicate that sedimentation constitutes the largest factor driving recent methane hydrate formation at Site U1517, and we suggest that sedimentation may play a larger role in gas hydrate dynamics along margins than previously recognized.
Plain Language Summary
Methane hydrate, which is a solid material/compound containing methane within frozen cages of water molecules, forms in continental margin sediments beneath the seafloor within a limited range of temperature and pressure. Researchers have previously suggested that sea level change during glaciations would allow methane hydrate to destabilize. This could free methane, cause slope failures, and affect Earth's climate. Drilling of sediments at a site offshore of New Zealand found evidence for recent trapping of methane as hydrate, and we investigate whether the hydrate formation is related to sea level changes associated with glaciation. We use computer models to test how methane hydrate storage would change through 400,000 years of variations in sea level and bottom water temperature. We find that expected water temperature changes during glacial cycles partially counteract the pressure effects of sea level changes. Rapid burial by sediment deposition appears to be the largest factor in storage and release of methane from hydrates at this site and perhaps at other continental margins worldwide.
Key Points
Pore water chloride concentrations at a Hikurangi Margin site suggest recent methane hydrate formation
Simulations suggest that sedimentation rates averaging 0.8 mm/year at this site drive gas hydrate dynamics and recent hydrate formation
Bottom water cooling during glaciation could counteract the impacts on methane hydrate stability of sea level decrease
Screaton et al. (2019, https://doi.org/10.1029/2019GC008603) examined the role of sedimentation, sea level, and bottom water temperature (BWT) changes due to glaciation as drivers for the downward ...migration of the base of gas hydrate stability and gas hydrate formation. International Ocean Discovery Program (IODP) Site U1517 in the Hikurangi margin was used as a case study because data at this site document a marked increase in chloride over a broad depth range, which was attributed to recent gas hydrate formation. In a comment on Screaton et al. (2019, https://doi.org/10.1029/2019GC008603), Sultan (2020, https://doi.org/10.1029/2019gc008846) used a linear thermal profile to argue that inferences and characterization of methane hydrate at IODP Site U1517 were incorrect because some occur below his estimated base of gas hydrate stability (BGHS). Based on this apparent discrepancy, Sultan (2020, https://doi.org/10.1029/2019gc008846) further stated that low‐chloride spikes may be unreliable indicators of methane hydrate occurrence. In this reply, we emphasize that unsteady‐state, and thus nonlinear, thermal profiles are likely in areas experiencing active sedimentation and bottom‐water temperature (BWT) changes. The resulting deviation from steady‐state temperature profile shifts the BGHS downward. In addition, sedimentation has the potential to bury methane hydrate more rapidly than it dissociates, helping to explain how methane hydrate could be observed below the BGHS. We also review the supporting evidence for gas‐hydrate occurrence at Site U1517 and the criteria used for Site U1517 site selection.
Key Points
Site U1517 gas hydrate inferred pore‐water chloride concentrations are supported by geophysical evidence
Unsteady‐state temperature profiles in subseafloor sediments can affect estimates of gas hydrate stability
Sedimentation can bury methane hydrates below the base of gas hydrate stability
One poorly understood feature of the subduction inputs to the Nankai Trough subduction zone (SW Japan) is a stratigraphic interval with an anomalously high porosity zone (HPZ), which is up to 240m ...thick and located within the clay- and volcanic ash-rich Shikoku Basin facies. To investigate the origin of their peculiar physical properties, we integrated logging-while-drilling (LWD) data, shipboard density measurements, and visual descriptions of core samples recovered from four drill sites of the Ocean Drilling Program and Integrated Ocean Drilling Program. We combined those observations with scanning electron microscopy (SEM) and laboratory consolidation tests on both HPZ samples and artificial mixtures of ash (glass shards)+smectite and vesicular pumice+smectite. LWD data indicate that the HPZ mudstones have a large proportion of dispersed volcanic ash (~20–30%). The consolidation tests show that the rate of porosity loss with increasing effective stress (consolidation behavior) is consistent among HPZ specimens and matches artificial mixtures containing up to 60% volcanic material. However, absolute values of porosity remain higher for HPZ samples compared to artificial mixtures, so processes in addition to the mechanical effects of volcanic clasts must be contributing. We suggest that hydration and partial dissolution turns clusters of volcanic glass into aggregates with distinct microfabric. SEM images confirm the presence of strengthened grain-to-grain contacts, which probably inhibit the collapse of the intra-aggregate pore space. The aggregates behave like grains, so that cohesive strength of the bulk sediment and rate of porosity loss remain nearly unchanged during burial. The two-step diagenetic process of dissolution and precipitation depends critically on a threshold abundance of fine-grained dispersed volcanic ash/pumice. Older units in the Shikoku Basin with only traces of dispersed ash show no such effects. HPZs should be expected in other subduction zones with similar compositional and diagenetic prerequisites.
•Abundant dispersed ash in high porosity zone (HPZ)•Altered volcanic glass forms aggregates•Cements maintain intra-aggregate porosity
Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (
λ
*
=
(
u
−
u
h
)
(
σ
v
...h
'
)
) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (
1
/
t
) requires much less decay time to achieve a desirable accuracy than an inverse time (1/
t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.
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