Top-Down Control of Motor Cortex Ensembles by Dorsomedial Prefrontal Cortex

SummaryDorsomedial prefrontal cortex is critical for the temporal control of behavior. Dorsomedial prefrontal cortex might alter neuronal activity in areas such as motor cortex to inhibit temporally inappropriate responses. We tested this hypothesis by recording from neuronal ensembles in rodent dorsomedial prefrontal cortex during a delayed-response task. One-third of dorsomedial prefrontal neurons were significantly modulated during the delay period. The activity of many of these neurons was predictive of premature responding. We then reversibly inactivated dorsomedial prefrontal cortex while recording ensemble activity in motor cortex. Inactivation of dorsomedial prefrontal cortex reduced delay-related firing, but not response-related firing, in motor cortex. Finally, we made simultaneous recordings in dorsomedial prefrontal cortex and motor cortex and found strong delay-related temporal correlations between neurons in the two cortical areas. These data suggest that functional interactions between dorsomedial prefrontal cortex and motor cortex might serve as a top-down control signal that inhibits inappropriate responding

A practical autonomous path planner for turn-of-the-century planetary microrovers

With the success of Mars Pathfinder's Sojourner rover, a new era of planetary exploration has opened, with demand for highly capable mobile robots. These robots must be able to traverse long distances over rough, unknown terrain autonomously, under severe resource constraints. Based on the authors' firsthand experience with the Mars Pathfinder mission, this paper reviews issues which are critical for successful autonomous navigation of planetary rovers. No currently proposed methodology addresses all of these issues. We next report on the 'Wedgebug' algorithm, which is applicable to planetary rover navigation in SE(2). The Wedgebug algorithm is complete, correct, requires minimal memory for storage of its worked model, and uses only on-board sensors, which are guided by the algorithm to efficiently senses only the data needed for motion planning. The implementation of a version of Wedgebug on the Rocky7 Mars Rover prototype at the Jet Propulsion Laboratory is described, and experimental results from operation in simulated martian terrain are presented

The nature of iron-oxygen vacancy defect centers in PbTiO3

The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of 1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.

Preliminary Geologic Description S.A. Holditch & Associates SFE No. 2

Four intervals of the Travis Peak Formation were cored in the S. A. Holditch & Associates SFE No. 2 well, North Appleby field, Nacogdoches County, Texas. Core was recovered from 8,230.0 to 8,319.7 ft, 8,678.2 to 8,738.0 ft, 9,480.0 to 9,572.1 ft, and 9,806.7 to 9,942.1 ft. The top of the Travis Peak is at 8,000 ft (log depth), so the core samples are from 230 ft to 1,942 ft below the top of the formation.Bureau of Economic Geolog

A practical autonomous path planner for turn-of-the-century planetary microrovers

With the success of Mars Pathfinder's Sojourner rover, a new era of planetary exploration has opened, with demand for highly capable mobile robots. These robots must be able to traverse long distances over rough, unknown terrain autonomously, under severe resource constraints. Based on the authors' firsthand experience with the Mars Pathfinder mission, this paper reviews issues which are critical for successful autonomous navigation of planetary rovers. No currently proposed methodology addresses all of these issues. We next report on the 'Wedgebug' algorithm, which is applicable to planetary rover navigation in SE(2). The Wedgebug algorithm is complete, correct, requires minimal memory for storage of its worked model, and uses only on-board sensors, which are guided by the algorithm to efficiently senses only the data needed for motion planning. The implementation of a version of Wedgebug on the Rocky7 Mars Rover prototype at the Jet Propulsion Laboratory is described, and experimental results from operation in simulated martian terrain are presented

Site Selection for Gri Cooperative Tight Gas Field Resesarch Volume 2: Geologic Characteristics of Selected Low-Permeability Gas Sandstones

Geological, engineering, and economic data on selected formations were compiled to provide a basis for siting the fourth Staged Field Experiment (SFE) for the Tight Gas Sands research program. The geologic units chosen are the Abo, Cleveland, and Frontier Formations, and the Mesaverde Group. Extrapolation potential is good for all formations except the Cleveland, whose thin deltaic package has no good analogy in other low-permeability sandstones. The Abo has the best potential for extrapolation to other low-permeability formations. The average thickness of reservoirs is about 250 ft in the Mesaverde and Abo, 160 ft in the Frontier, and 120 ft in the Cleveland. The deepest production depth varies from 4,750 ft (Abo) to 12,198 ft (Second Frontier sandstone). The estimated resource base ranges from 3 TCF (Abo) to 86 TCF (Mesaverde). Pre-stimulation production ranges from too small to measure (Cleveland, Frontier, Mesaverde) to 314 MCFD (Frontier). Post-stimulation production ranges from 3 MCFD (Mesaverde) to 12,250 MCFD (Cleveland). Permeability ranges from less than 0.0001 md (Frontier) to 1.3 md (Frontier). Natural fractures have been shown to be significant locally in the Mesaverde, but their contribution to reservoir permeability in the other formations is not well-documented.Bureau of Economic Geolog

Ammonia emissions from cattle urine and dung excreted on pasture

Twelve cattle were kept for three days in a circular area of 16 m radius on short pasture and fed with freshly-cut pasture. Ammonia (NH<sub>3</sub>) emissions from the urine and dung excreted by the cattle were measured with a micrometeorological mass-balance method, during the cattle presence and for 10 subsequent days. Daily-integrated emission rates peaked on Day 3 of the experiment (last day of cattle presence) and declined steadily for five days thereafter. Urine patches were the dominant sources for these emissions. On Day 9, a secondary emissions peak occurred, with dung pats likely to be the main sources. This interpretation is based on simultaneous observations of the pH evolution in urine patches and dung pats created next to the circular plot. Feed and dung samples were analysed to estimate the amounts of nitrogen (N) ingested and excreted. Total N volatilised as NH<sub>3</sub> was 19.8 (± 0.9)% of N intake and 22.4 (± 1.3)% of N excreted. The bimodal shape of the emissions time series allowed to infer separate estimates for volatilisation from urine and dung, respectively, with the result that urine accounted for 88.6 (± 2.6)% of the total NH<sub>3</sub> emissions. The emissions from urine represented 25.5 (± 2.0)% of the excreted urine-N, while the emissions from dung amounted to 11.6 (± 2.7)% of the deposited dung-N. Emissions from dung may have continued after Day 13 but were not resolved by the measurement technique. A simple resistance model shows that the magnitude of the emissions from dung is controlled by the resistance of the dung crust

Geology of the Lower Cretaceous Travis Peak Formation, East Texas: Characterization of a Tight Gas SandStone

Since 1982, the Gas Research Institute (GRI) Tight Gas Sands Project has supported geological investigations designed to develop knowledge necessary to efficiently produce low-permeability, gas-bearing sandstones. As part of that program, the Bureau of Economic Geology has conducted research on low-permeability sandstone in the Lower Cretaceous Travis Peak (Hosston) Formation in East Texas. The first phase of the study, which lasted from 1983 until 1986, involved extensive collection of core and production data in seven cooperative wells. Information gained from the cooperative wells, combined with geologic characterization of the Travis Peak throughout the study area, led to the drilling by GRI of three Staged Field Experiment (SFE) wells between 1986 and 1988. The SFE wells were drilled and completed by GRI specifically for the purpose of research on low-permeability gas reservoirs. This report summarizes the results of the geologic studies of the Travis Peak Formation, and it focuses on the contribution of geology to evaluation and completion of tight gas sandstone wells.Bureau of Economic Geolog

Ammonia emissions from cattle urine and dung excreted on pasture

Twelve cattle were kept for three days in a circular area of 16 m radius on short pasture and fed with freshly-cut pasture. Ammonia (NH₃) emissions from the urine and dung excreted by the cattle were measured with a micrometeorological mass-balance method, during the cattle presence and for 10 subsequent days. Daily-integrated emission rates peaked on Day 3 of the experiment (last day of cattle presence) and declined steadily for five days thereafter. Urine patches were the dominant sources for these emissions. On Day 9, a secondary emissions peak occurred, with dung pats likely to be the main sources. This interpretation is based on simultaneous observations of the pH evolution in urine patches and dung pats created next to the circular plot. Feed and dung samples were analysed to estimate the amounts of nitrogen (N) ingested and excreted. Total N volatilised as NH₃ was 19.8 (± 0.9)% of N intake and 22.4 (± 1.3)% of N excreted. The bimodal shape of the emissions time series allowed to infer separate estimates for volatilisation from urine and dung, respectively, with the result that urine accounted for 88.6 (± 2.6)% of the total NH₃ emissions. The emissions from urine represented 25.5 (± 2.0)% of the excreted urine-N, while the emissions from dung amounted to 11.6 (± 2.7)% of the deposited dung-N. Emissions from dung may have continued after Day 13 but were not resolved by the measurement technique. A simple resistance model shows that the magnitude of the emissions from dung is controlled by the resistance of the dung crust. © Author(s) 2013

Geology of the Lower Cretaceous Travis Peak Formation, East Texas: Depositional History, Diagenesis Structure and Reservoir Engineering Implications

This report summarizes stratigraphic, petrographic, and structural studies of the Lower Cretaceous Travis Peak Formation, a low-permeability gas sandstone in East Texas, and presents reservoir engineering implications. Depositional systems in this region were interpreted from logs and cores and include (1) a braided- to meandering-fluvial system that forms the majority of the Travis Peak section; (2) deltaic deposits interbedded with the distal part of the fluvial system; (3) paralic deposits that overlie and interfinger with the deltaic and fluvial deposits near the top of the Travis Peak; and (4) shelf deposits present at the downdip extent of the formation. Petrographic studies indicate the sandstones are quartzarenites and subarkoses. Cementation by quartz, dolomite, ankerite, illite, chlorite, and reservoir bitumen have reduced porosity to less than 8 percent and permeability to less than 0.1 md throughout most of the formation. Structurally deeper sandstones are more intensely quartz cemented than are shallower sandstones and contain abundant, open natural fractures. Borehole breakouts and drilling-induced fractures in core can be used to predict horizontal stress directions and the direction of hydraulic fracture propagation. Hydraulic fractures propagate in directions subparallel to the east-northeast strike of the natural fractures; thus, hydraulically induced fractures may not intersect many natural fractures.Bureau of Economic Geolog