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We study the problem of maximizing the probability that (i) an electric component or financial institution $X$ does not default before another component or institution $Y$ and (ii) that $X$ and $Y$ default jointly within the class of all random variables $X,Y$ with given univariate continuous distribution functions $F$ and $G$, respectively, and show that the maximization problems correspond to finding copulas maximizing the mass of the endograph $\Gamma^\leq(T)$ and the graph $\Gamma(T)$ of $T=G \circ F^-$, respectively. After providing simple, copula-based proofs for the existence of copulas attaining the two maxima $\overline{m}_T$ and $\overline{w}_T$ we generalize the obtained results to the case of general (not necessarily monotonic) transformations $T:[0,1] \rightarrow [0,1]$ and derive simple and easily calculable formulas for $\overline{m}_T$ and $\overline{w}_T$ involving the distribution function $F_T$ of $T$ (interpreted as random variable on $[0,1]$). The latter are then used to charac\-terize all non-decreasing transformations $T:[0,1] \rightarrow [0,1]$ for which $\overline{m}_T$ and $\overline{w}_T$ coincide. A strongly consistent estimator for the maximum probability that $X$ does not default before $Y$ is derived and proven to be asymptotically normal under very mild regularity conditions. Several examples and graphics illustrate the main results and falsify some seemingly natural conjectures., Comment: 27 pages, 4 figures

OBJECTIVE The US-based Spinal Laminectomy versus Instrumented Pedicle Screw (SLIP) trial reported improvement in disability following laminectomy with fusion versus laminectomy alone for patients with lumbar spondylolisthesis. Despite using similar methods, a concurrent Swedish trial investigating the same question did not reach the same conclusion. The authors performed a simulation-based analysis to elucidate potential causes of these divergent results. METHODS The mean and standard deviation of the preoperative and 2-year postoperative Oswestry Disability Index (ODI) scores for each study group (laminectomy with fusion and laminectomy alone) were collected from the spondylolisthesis stratum of the Swedish trial and used to create a MATLAB simulator using linear transformations to predict postoperative ODI distributions. Applying this simulator to both varied and published preoperative ODI distributions from the SLIP trial, the authors simulated the results of the US-based trial using treatment effects from the Swedish study and compared simulated US results to those published in the SLIP trial. RESULTS Simulated US results showed that as preoperative disability increased, the difference in postoperative ODI scores grew between treatment groups and increasingly favored laminectomy alone (p < 0.0001). In 100 simulations of a similarly sized US trial, the average mean change in ODI scores postoperatively was significantly higher than was published for laminectomy alone in the SLIP trial (−21.3 vs −17.9), whereas it was significantly lower than published for fusion (−16.9 vs −26.3). CONCLUSIONS The expected benefit of surgical treatments for spondylolisthesis varied according to preoperative disability. Adapting Swedish-estimated treatment effects to the US context mildly overapproximated the improvement in postoperative disability scores for laminectomy, but more severely underapproximated the improvement reported for laminectomy and fusion in the SLIP trial. The observed heterogeneity between these studies is influenced more by patient response to fusion than response to laminectomy. This analysis paves the way for future studies on the impact of preoperative treatment group heterogeneity, differences in surgical methods, and empirical design on reported clinical benefits. Although bayesian reanalysis of published randomized controlled trial data is susceptible to biases that typically limit post hoc analyses, the authors’ method offers a simple and cost-effective approach to improve the understanding of published clinical trial results and their implications for future studies.

Study design Observational study. Objectives To evaluate the prevalence of erectile dysfunction and evaluate the effects of decompressive surgery on erectile dysfunction in cervical spinal stenosis and lumbar canal stenosis patients. Methods This observational, prospective analysis enrolled patients aged 18-80 with cervical spinal stenosis and/or lumbar canal stenosis that underwent respective decompressive surgery. The IIEF-5 questionnaire was administered preoperatively, and at 6- and 12-months postoperatively to assess erectile dysfunction severity. The EPIC database was queried to determine any postoperative complications and document prominent erectile dysfunction risk factors. Results Of 79 patients included in the analysis, 42 (53.2%) completed the IIEF-5 at 6 months, and 62 (78.5%) completed it at 12 months. Eighteen had cervical stenosis only, 54 had lumbar stenosis only, and 7 had both. 72% (18/25) of cervical stenosis patients and 83.6% (51/61) of lumbar stenosis patients had erectile dysfunction preoperatively according to IIEF-5 responses. The average preoperative IIEF-5 score indicated significant presence of erectile dysfunction for both the cervical and lumbar stenosis groups. No significant differences were identified in IIEF-5 score deltas from pre- to both postoperative periods. The presence of erectile dysfunction in both the cervical and lumbar stenosis groups was not significantly associated with the presence of any documented risk factors. Conclusions Our results suggest no significant improvement in overall erectile function postoperatively for patients with preoperative erectile dysfunction. This is important to address during patient counseling for decompression surgery candidates with cervical spinal stenosis and/or lumbar canal stenosis to manage expectations.

Study Design Systematic review and Meta-analysis. Objective This systematic review seeks to compare fusion, reoperation and complication rates, estimated blood loss (EBL), and surgical time between multi-level instrumented fusions with LIVs (lowest instrumented vertebra) in the cervical spine and those that extend into the thoracic spine. Summary of Background Data Several studies address the question of whether to extend a long-segment, posterior cervical fusions, performed for degenerative disease, into the upper thoracic spine. Recommendations for appropriate LIV continue to vary. Methods A comprehensive computerized literature search through multiple electronic databases without date limits up until April 3rd, 2020 using combinations of key search terms and sets of inclusion/exclusion criteria was performed. Results Our comprehensive literature search yielded 3852 studies. Of these, 8 articles consisting of 1162 patients were included in the meta-analysis. In 61.2% of the patients, the fusion did not cross the cervicothoracic junction (CTJ) (cervical LIV, CLV). In the remaining 38.8%, the fusion extended into the upper thoracic spine (thoracic LIV, TLV). Overall, mean patient age was 62.5 years (range: 58.8-66.1 years). Our direct analysis showed that odds of fusion were not statistically different between the CLV and TLV groups (OR: .648, 95% CI: .336-1.252, P = .197). Similarly, odds of reoperation (OR: 0.726, 95% CI: 0.493-1.068, P = .104) and complication rates were similar between the 2 groups (OR: 1.214, 95% CI: 0.0.750-1.965, P = .430). Standardized mean difference (SMD) for the blood loss (SMD: .728, 95% CI: 0.554-.901, P = .000) and operative (SMD: 0.653, 95% CI: .479-.826, P = .000) differed significantly between the 2 groups. The indirect analysis showed similar fusion (Effect Size (ES)TLV: .892, 95% CI: .840-.928 vs ESCLV:0.894, 95% CI:0.849-.926); reoperation rate (ESTLV:0.112, 95% CI: 0.075-.164 vs ESCLV: .125, 95% CI: .071-.211) and complication rates (ESTLV: .108, 95% CI: .074-.154 vs ESCLV:0.081, 95% CI: .040-.156). Conclusions Our meta-analysis showed that fusion, complication, and reoperation rates did not differ significantly between patients in whom multi-level posterior fusions ended in the cervical spine vs those of which was extended into the thoracic spine. The mean blood loss, operative time and length of stay were significantly lower in patients with CLV at C6 or C7, compared to their counterparts. These data suggest that, absent focal, C7-T1 pathology, extension of long, posterior cervical fusions into the thoracic spine may not be necessary.

Virtual encounters have experienced an exponential rise amid the current COVID-19 crisis. This abrupt change, seen in response to unprecedented medical and environmental challenges, has been forced upon the orthopaedic community. However, such changes to adopting virtual care and technology were already in the evolution forecast, albeit in an unpredictable timetable impeded by regulatory and financial barriers. This adoption is not meant to replace, but rather augment established, traditional models of care while ensuring patient/provider safety, especially during the pandemic. While our department, like those of other institutions, has performed virtual care for several years, it represented a small fraction of daily care. The pandemic required an accelerated and comprehensive approach to the new reality. Contemporary literature has already shown equivalent safety and patient satisfaction, as well as superior efficiency and reduced expenses with musculoskeletal virtual care (MSKVC) versus traditional models. Nevertheless, current literature detailing operational models of MSKVC is scarce. The current review describes our pre-pandemic MSKVC model and the shift to a MSKVC pandemic workflow that enumerates the conceptual workflow organization (patient triage, from timely care provision based on symptom acuity/severity to a continuum that includes future follow-up). Furthermore, specific setup requirements (both resource/personnel requirements such as hardware, software, and network connectivity requirements, and patient/provider characteristics respectively), and professional expectations are outlined. MSKVC has already become a pivotal element of musculoskeletal care, due to COVID-19, and these changes are confidently here to stay. Readiness to adapt and evolve will be required of individual musculoskeletal clinical teams as well as organizations, as established paradigms evolve. Cite this article: Bone Joint Open 2020;1-6:272–280.

Marcellus Shale drilling is a relatively new activity that has expanded natural gas resources in the United States. Although many assumed Marcellus Shale was sterile due to extreme conditions endured since deposition, conditions present in the shale today are within range where microorganisms can occur. Here, we consider whether some microbes seen in produced fluids from Marcellus Shale drilling may be native by comparing organisms found in core samples and produced fluids to those found in injected fluids from active wells in Pennsylvania. Illumina sequencing was used to identify organisms based on 16s rRNA barcoding regions of DNA extracts from Marcellus Shale samples. Identified microbial communities were then compared using principal components analysis and SourceTracker tools. Frequency of homology between sequences showed that produced fluids contained more microorganisms in common with shale cores than with injected fluids. Principal components analysis and SourceTracker corroborated these results. Possible native organisms found in these samples included radiotolerant extremophiles such as Deinococcus radiodurans. This work suggests that deep subsurface Marcellus Shale, previously believed sterile, may contain native microorganisms, which may have been deposited during the original deposition or migrated into the deep subsurface Marcellus during a more recent water influx. Additional investigation is recommended.

Motivated by the increasing popularity and the seemingly broad applicability of pair-copula constructions underlined by numerous publications in the last decade, in this contribution we tackle the unavoidable question on how flexible and simplifying the commonly used `simplifying assumption' is from an analytic perspective and provide answers to two related open questions posed by Nagler and Czado in 2016. Aiming at a simplest possible setup for deriving the main results we first focus on the three-dimensional setting. We prove that the family of simplified copulas is flexible in the sense that it is dense in the set of all three-dimensional co\-pulas with respect to the uniform metric $d_\infty$ - considering stronger notions of convergence like the one induced by the metric $D_1$, by weak conditional convergence, by total variation, or by Kullback-Leibler divergence, however, the family even turn out to be nowhere dense and hence insufficient for any kind of flexible approximation. Furthermore, returning to $d_\infty$ we show that the partial vine copula is never the optimal simplified copula approximation of a given, non-simplified copula $C$, and derive examples illustrating that the corresponding approximation error can be strikingly large and extend to more than 28\% of the diameter of the metric space. Moreover, the mapping $\psi$ assigning each three-dimensional copula its unique partial vine copula turns out to be discontinuous with respect to $d_\infty$ (but continuous with respect to $D_1$ and to weak conditional convergence), implying a surprising sensitivity of partial vine copula approximations. The afore-mentioned main results concerning $d_\infty$ are then extended to the general multivariate setting., Comment: 36 pages, 3 figures

Background: Lumbar spinal stenosis can cause symptomatic neurogenic claudication alongside radicular pain and weakness. In appropriately selected patients, surgical intervention has been demonstrated to provide for improvement in pain, disability, and quality of life. This systematic review sought to define the utility and safety of such decompression with or without arthrodesis in the management of symptomatic lumbar spinal stenosis for elderly patients older than 65 years of age. Methods: A systematic review was conducted using MEDLINE for literature published through December 2014. The first question focused on the effectiveness of lumbar spinal surgery for symptomatic lumbar spinal stenosis in elderly patients (over age 65 y). The second question focused on safety of surgical intervention on this elderly population with emphasis on perioperative complication rates. Results: Review of 11 studies reveals that the majority of elderly patients exhibit significant symptomatic improvement, with overall benefits observed for pain (change visual analog scale 4.4 points) and disability (change Oswestry Disability Index 23 points). Review of 11 studies reveals that perioperative complications were infrequent and acceptable with pooled estimates of mortality (0.5%), inadvertent durotomy (5%), and wound infection (2%). Outcomes seem less favorable with greater complication rates among patients with diabetes or obesity. Conclusion: Based on largely low-quality, retrospective evidence, we recommend that elderly patients should not be excluded from surgical intervention for symptomatic lumbar spinal stenosis.

Grain size effects have been investigated in the lubricated sliding wear of three transparent magnesium aluminate (MgAl 2 O 4 ) spinel materials with different grains sizes identified as: Nano, Fine, and Coarse. Only Fine spinel shows classical wear behavior, which is characterized by initial mild wear followed by a sharp transition to severe fracture-controlled wear. Worn surfaces of Fine spinel show extensive grain pullout, consistent with intergranular mode of fracture found in that spinel. Nano and Coarse spinels both show gradual transition from mild wear to severe wear, and both have significantly lower overall wear rates compared to Fine spinel. Worn surfaces in both Nano and Coarse spinels show transgranular fracture and material removal, which is reminiscent of lateral-crack induced chipping. The transgranular fracture mode in Nano spinel can be attributed to stronger grain boundaries in that spinel, which could be due to the Y 2 O 3 sintering additive used for grain refinement. Whilst the large scale of the grains in Coarse spinel could be responsible for the transgranular fracture observed in that spinel.

In response to a need for improving the mechanical properties of optically transparent ceramics, the nanocomposites approach is used to strengthen transparent magnesium-aluminate spinel with Si 3 N 4 nanodispersoids. The as-processed nanocomposites are found to be >70% transparent in the critical infrared wavelength range of 3–4.5 μm. Mie scattering combined with absorption by the Si 3 N 4 nanodispersoids explains quantitatively the IR transmission behavior of these nanocomposites. The nanocomposites are also found to be transparent in the visible region. Upon heat treatment (1000 °C for 4 h in air), the optical properties of the nanocomposites remain unchanged. However, the heat treatment results in a 29% increase in the average strength, accompanied by almost doubling of the Weibull modulus, and an 85% increase in the indentation toughness. The improvements in mechanical properties after the heat treatment in these nanocomposites are explained qualitatively, based on generally accepted arguments involving surface-oxidation-induced surface compression and flaw-healing. While further work is needed to fully understand and exploit these effects, this first report on transparent nanocomposites could have broad implications for the creation of mechanically robust, transparent ceramics of the future.

Here, we show that nanostructured magnesium-aluminate spinel (MgAl2O4) with a highly uniform grain-size distribution can be fabricated using Y2O3 sintering additive for infrared (IR) window/dome applications. The average grain size of this nanostructured spinel is 345 nm, and the size of the largest grain is 970 nm. As a consequence this nanostructured spinel has high room-temperature strength (470 MPa) and reliability (Weibull modulus 6.2). It also has improved erosion resistance (sand and rain) and thermal-shock resistance. Near-theoretical in-line IR transmission is observed in this nanostructured spinel at room temperature, with an optical scatter of

Marcellus Shale occurs at depths of 1.5-2.5 km (5000 to 8000 feet) where most geologists generally assume that thermogenic processes are the only source of natural gas. However, methanogens in produced fluids and isotopic signatures of biogenic methane in this deep shale have recently been discovered. This study explores whether those methanogens are indigenous to the shale or are introduced during drilling and hydraulic fracturing. DNA was extracted from Marcellus Shale core samples, preinjected fluids, and produced fluids and was analyzed using Miseq sequencing of 16s rRNA genes. Methanogens present in shale cores were similar to methanogens in produced fluids. No methanogens were detected in injected fluids, suggesting that this is an unlikely source and that they may be native to the shale itself. Bench-top methane production tests of shale core and produced fluids suggest that these organisms are alive and active under simulated reservoir conditions. Growth conditions designed to simulate the hydrofracture processes indicated somewhat increased methane production; however, fluids alone produced relatively little methane. Together, these results suggest that some biogenic methane may be produced in these wells and that hydrofracture fluids currently used to stimulate gas recovery could stimulate methanogens and their rate of producing methane.

We present a case of massive spinal epidural hematoma with an atypical presentation characterized by unilateral, isolated motor deficit in the right lower extremity on postoperative day 2 after Collis-Nissen fundoplication and a T7-8 epidural for postoperative pain. The epidural had been placed in the preoperative theater before surgery. Subcutaneous unfractionated heparin was initiated 18 hours later on postoperative day 1 with 3 times daily dosing. The patient also received 3 doses of ketorolac starting 10 hours after epidural placement. Symptoms were first reported on postoperative day 2, 37 hours after epidural placement. Thoracic magnetic resonance imaging showed an epidural hematoma extending from T2 through T12, requiring emergent decompression and evacuation. The patient made a complete recovery without any resultant neurologic deficit.

Much of the research on height in historical populations relies on convenience samples. A crucial question with convenience samples is whether the sample accurately reflects the characteristics of the population; if not, then estimated parameters will be affected by sample selection bias. This paper applies a simple test for selection biased developed in Bodenhorn, Guinnane, and Mroz (2013) to several historical samples of prisoners, freed slaves, and college students. We reject the hypothesis of no selection bias in all cases. Using Roy's (1951) model of occupational choice, we interpret these findings as reflecting the economic forces that lead individuals to take the actions the led to inclusion in the sample. Our findings suggest that much of the evidence on the "industrialization puzzle" during the nineteenth century could reflect changing selection into the samples rather than changes in population heights.

Reversal of the normal cervical spine curvature, as seen in cervical kyphosis, can lead to mechanical pain, neurological dysfunction, and functional disabilities. Surgical intervention is warranted in patients with sufficiently symptomatic deformities in an attempt to correct the deformed cervical spine. In theory, improved outcomes should accompany a greater degree of correction toward lordosis, although there are few data available to test this relationship. The purpose of this study is to determine if the degree of deformity correction correlates with improvement in neurological symptoms following surgery for cervical kyphotic deformity.A retrospective review of 36 patients with myelopathic symptoms who underwent cervical deformity correction surgery between 2001 and 2009 was performed. Preoperative and postoperative radiographic findings related to the degree of kyphosis were collected and compared with functional outcome measures. The minimum follow-up time was 2 years.A significant relationship was observed between a greater degree of focal kyphosis correction and improved neurological outcomes according to the modified Japanese Orthopaedic Association (mJOA) score (r = -0.46, p = 0.032). For patients with severe neurological symptoms (mJOA score12) a trend toward improved outcomes with greater global kyphosis correction was observed (r = -0.56, p = 0.057). Patients with an mJOA score less than 16 who attained lordosis postoperatively had a significantly greater improvement in total mJOA score than patients who maintained a kyphotic position (achieved lordosis: 2.7 ± 2.0 vs maintained kyphosis: 1.1 ± 2.1, p = 0.044).The authors' results suggest that the degree of correction of focal kyphosis deformity correlates with improved neurological outcomes. The authors also saw a positive relationship between attainment of global lordosis and improved mJOA scores. With consideration for the risks involved in correction surgery, this information can be used to help guide surgical strategy decision making.

This study develops a discrete multiple state duration model for screen- ing a chronic disease that allows for duration dependence, unmeasured heterogeneity, partial observability of the state and endogenous treat- ment. We study whether screening for diabetes is e¤ective in delaying progression of complications of the lower extremities. Our results show that early diagnoses of diabetes reduces the probabilities of transitioning to a worse disease stage, death or amputation. In particular, decreasing the time screening for the onset of diabetes from every four years to once a year after age 65 saves: 54 lives, 10 amputations, and 89 lower extremity complications of 10,000 individuals by age 80.

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) established an Extreme Drilling Lab to engineer effective and efficient drilling technologies viable at depths greater than 20,000 feet. This paper details the challenges of ultra-deep drilling, documents reports of decreased drilling rates as a result of increasing fluid pressure and temperature, and describes NETL’s Research and Development activities. NETL is invested in laboratory-scale physical simulation. Their physical simulator will have capability of circulating drilling fluids at 30,000 psi and 480 °F around a single drill cutter. This simulator will not yet be operational by the planned conference dates; therefore, the results will be limited to identification of leading hypotheses of drilling phenomena and NETL’s test plans to validate or refute such theories. Of particular interest to the Extreme Drilling Lab’s studies are the combinatorial effects of drilling fluid pressure, drilling fluid properties, rock properties, pore pressure, and drilling parameters, such as cutter rotational speed, weight on bit, and hydraulics associated with drilling fluid introduction to the rock-cutter interface. A detailed discussion of how each variable is controlled in a laboratory setting will be part of the conference paper and presentation.

IntroductionMagnetic resonance imaging (MRI) is a vital tool for detection of instability and soft tissue trauma following cervical spine injuries (CSIs). However, high cost, prolonged imaging time...

New military requirements have reinvigorated the need for transparent magnesium aluminate (MgAl2O4) spinel. Surmet has developed a process that yields high quality transparent spinel at production scale. Several issues related to the extreme requirements of processing ultrafine spinel powders are described. Transmission data is presented for a significant dataset of parts made by this process. More recently, the process has been expanded to include a capability for producing domes for the Joint Common Missile program. Domes at nominal 6” and 7” diameter have been successfully fabricated. Despite early challenges related to the forming portion of the process, a repeatable capability for these domes has been demonstrated. Several challenges remain in spinel processing in order to support additional military requirements. In particular, the strength of the material needs further improvement. Also, improvements in optical quality with regard to inclusions are needed.

Abstract It is now clear that methane hydrates contain enormous volumes of natural gas and have the potential to play a major role in future global energy supplies. Recent developments indicate that the prospects for economic production of methane from hydrates are good, and could occur much sooner than previously thought. To ensure that the United States remains a leader in hydrates research and technology, the Department of Energy's (DOE) Strategic Center for Natural Gas (SCNG) at the National Energy Technology Laboratory (NETL) is charged with coordinating a comprehensive national research and development program in all aspects of methane hydrates. In advance of attempts at commercial exploitation, our program will support fundamental studies that will improve the understanding of the nature of hydrates, the impact of hydrates on the strength and stability of ocean-bottom sediments, and the interaction of the global hydrate reservoir with the world's oceans and atmosphere. This report outlines these key methane hydrate research and development (R&D) issues, reviews DOE's past and current hydrate programs, and outlines our plans for a coordinated and collaborative R&D program in which the nation's best minds are efficiently brought to bear on the challenge of maximizing the potential benefits of natural methane hydrates. Introduction At present, the United States is relying on the accelerated use of clean and affordable natural gas to simultaneously achieve aggressive economic and environmental goals. Fundamental to this strategy is an abundant and affordable supply of domestic natural gas. However, there are increasing concerns about the surety of this supply. In a recent workshop on post-2020 gas supplies held at the DOE's NETL, most organizations agreed that a new source of supply would most likely be needed by the year 2030. That new source will likely be methane hydrates. Clearly, no one institution has the resources and the expertise to quickly resolve the many issues and technological challenges surrounding the possible exploitation of methane hydrates. Similarly, a series of parallel, duplicative, and uncoordinated efforts will inevitably delay results and may leave key questions unanswered. The NETL believes that a nationally coordinated, collaborative effort is needed, and is committed to supporting a program of allied and focused investigations by the nation's leading researchers on all fronts of the methane hydrate issue. Methane Hydrate R&D Issues Methane Hydrates are the most abundant natural form of clathrate - unique chemical substances in which molecules of one material (in this case, water) form an open solid lattice that encloses, without chemical bonding, appropriately-sized molecules of another material (in this case, methane). Recent investigations have revealed that the widespread occurrence of both methane and water allows methane hydrates to accumulate virtually everywhere pressures and temperatures are suitable. As a result, evidence of hydrates is being discovered at relatively shallow depths beneath arctic permafrost and within the fine-grained clastic sediments on the slopes and rises of continental shelves around the world.

Abstract The U.S. Department of Energy (DOE), National Energy Technology Laboratory has been conducting research on low permeability gas reservoirs for over 30 years. Major field experiments like the multiwell experiment and the multi-site experiment at Rifle, Colorado, have provided tremendous insight into the characterization of low permeability gas sands, the associated natural fracture network, and the implications of hydraulic fracturing. Since the early 1990's, the DOE has focused its research efforts on developing technologies and methodologies to detect and characterize natural fractures in the subsurface and on demonstrating methods for enhancing production. Several successful technology advances are expected to have significant impact on the recovery of natural gas from low permeability formations. A horizontal well recently completed at 15,000 feet in the Frontier Formation in Wyoming, in conjunction with Union Pacific Resources (UPR), initially flowed 14 MMcfd and in the first 9 months recovered 2.75 Bcf of gas. UPR has two more wells underway and plans to drill additional wells based on the success of this project. Natural fracture detection techniques have been successfully demonstrated in existing fields in the Piceance and Wind River basins. An integrated 3-D seismic and geomechanical modeling approach was demonstrated in the Piceance basin and more recently in conjunction with the horizontal well drilled by UPR/DOE. The use of 3-D seismic attributes was demonstrated in the Wind River Basin. DOE initiated several new projects to begin work in October 1999 that willdemonstrate the use of natural fracture detection technologies as an exploration tool andadvance the state-of-the-art in natural fracture detection by developing new techniques to quantify fracture properties that control the flow and transport of gas. This paper will provide a detailed discussion for the projects that have recently been completed and for the new projects along with their implications for enhancing gas production from low permeability gas reservoirs. Introduction As new discoveries from conventional supplies decline, future supplies of natural gas will increasingly have to come from low permeability (tight) reservoirs. Basins containing significant resources and reserves include the Greater Green River, Piceance, Wind River, Uinta, and Anadarko. Other basins and plays also hold large resources of gas. The 1992 National Petroleum Council's (NPC) natural gas study1 concluded that 232 Tcf could be technically recoverable from low permeability sand formations. Assuming that technology improvements continued, the NPC estimated that 349 Tcf could be produced. In their most recent study2, the NPC states that "deeper wells, deeper water and nonconventional sources will be the key to future supply." Nonconventional production in the Rocky Mountain region is projected to increase by 1 Tcf per year by 2010 and as much as 1.5 Tcf per year by 2015. Significant technology hurdles must be addressed and overcome to assure a cost-competitive supply from these sources. Gas production from low permeability formations is hindered by the formations' capability to allow gas to flow to the wellbore. Hence, economic production of natural gas can only occur where the flow path to the wellbore is enhanced. Geologic processes have created natural fractures in most formations that provide channels for gas to flow. In areas where the natural fracture network is extensive and dense, economic production can be achieved without wellbore enhancements. However, most low permeability formations require hydraulic fracturing to connect the wellbore to the formation to allow commercial production. The challenges facing industry are locating the areas of dense fracture networks and determining whether horizontal wells or vertically stimulated wells are more economical.

Abstract The U.S. Department of Energy/Morgantown Energy Technology Center (METC), through partnerships with industry, is demonstrating the importance of geologic modeling and reservoir simulation for optimizing the development and operation of gas storage fields. METC entered into a Cooperative Research and Development Agreement with National Fuel Gas Supply Corporation (NFGSC) to investigate the expansion of an existing gas storage field in western New York. A geologic model of the reservoir was developed using data from 14 existing vertical wells, mainly concentrated in the center of the field. A good history match of simulator predicted and field measured flowing wellhead pressure was achieved through 2.5 injection and withdrawal cycles. Biannual inventory shut-in pressures were matched within 5 percent. Forecasts of reservoir performance were made for various field development strategies that included the operation of 11 existing vertical wells plus (1)14 additional vertical wells, (2) four, 2000-foot horizontal wells, and (3) a combination of horizontal and vertical wells. Although there has been no field verification of the modeling results, the results of the study have shown that geologic modeling and reservoir simulation can be very important to the efficient development of a storage reservoir. The modeling results have shown the possible advantages of using horizontal wells and have also focused efforts to gather additional data necessary to make the final decision on a field development strategy. While cost savings opportunities have been identified through this modeling effort with NFGSC, the need for additional reservoir description will require three to four vertical step-out wells before proceeding with full field development, especially with horizontal wells. Introduction A more efficient natural gas storage system will be essential for supporting the expected growth in U.S. gas demand. A mission of the METC Gas Storage and Delivery Program is to assist industry, through cooperative demonstration studies of selected storage fields, to increase storage efficiency, i.e., increase deliverability and capacity, and reduce development costs. A promising technology for increasing storage efficiency is horizontal wells. Thousands of horizontal wells have been drilled for exploration and production with great success, yet the application of this technology in the storage industry has been very limited. Several horizontal wells that have been drilled in gas storage fields, for which the results have been reported have shown deliverability increases of 4-7 times over vertical wells. Horizontal wells, however, are not a cure-all and must be carefully studied to determine their usefulness and profitability. Thus, a second objective of the cooperative efforts between METC and industry is to show the cost benefit of using geologic modeling and reservoir simulation to "optimize" field development strategies. The model results have shown the possible advantages of using horizontal well technology and have also focused efforts to gather the additional data necessary to make the final decision on field development strategy.

Ti3SiC2 showed a significant degree of corrosion resistance in contact with molten cryolite. Corrosion resistance was observed despite the oxidizing conditions employed and the significant portion of TiC contamination observed in hot-pressedparts. This favorable outcome supports proposed follow-up activities, including more extensive corrosion testing, more thorough characterization of the corroded material, and confirmation of the reported physical and electrical performance for the material. Following the successful conclusion of these tests, an evaluation of the material in a benchscale electrochemical cell can be performed.