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排序方式: 共有554条查询结果,搜索用时 15 毫秒
31.
32.
In this study, dissolved Kr and SF6 gases were used to determine various hydrogeological parameters of laboratory columns under water-saturated and partially saturated conditions as a function of the flow velocity. The dissolved gases behaved conservatively in saturated columns but were significantly retarded in unsaturated conditions as a direct function of the Henry's law constant (KH) and the ratio of column pore spaces filled with air and water (Vg/Vw). Lower aqueous diffusion coefficients for SF6 compared to that for Kr also resulted in significant rate-limited mass transport across gas-water interface. This effect was exacerbated at higher flow velocities as was indicated by the asymmetric shape of breakthrough curves, more so in the case of SF6. A nonequilibrium advective-dispersive transport model accurately described tracer breakthrough and was used to estimate parameters such as final Vg/Vw under partially saturated conditions and partitioning rates. Internally consistent model results were obtained for both dissolved gases despite the wide range in physical properties (e.g., KH and aqueous diffusion coefficients), suggesting that dissolved Kr and SF6 may be used in conjunction to delineate and validate aquifer characteristics simultaneously from a single pulse injection of the tracer. 相似文献
33.
Gross PA Patriaco D McGuire K Skurnick J Teichholz LE 《The Joint Commission journal on quality improvement》2002,28(10):566-573
BACKGROUND: Telemetry monitoring is widely used in hospitals; the importance of being able to monitor and examine dysrhythmias has been universally accepted. Yet it is often used for patients who do not actually require this technology. A model to improve the efficiency of telemetry use entailed the use of an advanced practice nurse (APN; identical to a nurse practitioner) to provide concurrent review and intervention of floating telemetry, which is available for patients independently of the floor location and who do not need an intensive care unit bed. ADDRESSING OVERUSE: The demand for floating telemetry at Hackensack University Medical Center had equaled or exceeded the telemetry availability virtually 100% of the time, even after local guidelines had been disseminated in 1998. The APN carried out concurrent monitoring and intervened with the attending physician when patients were on telemetry for longer than 48 hours and did not meet the local telemetry guidelines. RESULTS: The mean number (standard error [SE]) of hours per patient declined from 65.2 +/- 0.7 hours (95% confidence interval, 63.8 to 66.6 hours) for the 11 months before the intervention to a mean of 49.6 +/- 0.4 hours (95% confidence interval, 48.7 to 50.2 hours) for the 29 months after intervention--representing a decrease of 34% (p < 0.0001). This decrease led to an increase in the number of patients per month put on telemetry. DISCUSSION: The APN model, an aggressive approach that induced change almost immediately, was then applied to other quality improvement projects. 相似文献
34.
Needs for increased product quality, reduced pollution, and reduced energy and material consumption are driving enhanced process integration. This increases the number of manipulated and measured variables required by the control system to achieve its objectives. This paper addresses the question of whether processes tend to become increasingly more difficult to identify and control as the process dimension increases. Tools and results of multivariable statistics are used to show that, under a variety of assumed distributions on the elements, square processes of higher dimension tend to be more difficult to identify and control, whereas the expected controllability and identifiability of nonsquare processes depends on the relative numbers of measured and manipulated variables. These results suggest that the procedure of simplifying the control problem so that only a square process is considered is a poor practice for large scale systems. 相似文献
35.
Kathryn I Pollak Cheryl A Oncken Isaac M Lipkus Bercedis L Peterson Geeta K Swamy Pamela K Pletsch Pauline Lyna Rebecca J Namenek Brouwer Laura J Fish Evan R Myers 《Nicotine & tobacco research》2006,8(4):547-554
Improvements in smoking cessation interventions for pregnant smokers are needed. One major step is to examine the potential effectiveness of nicotine replacement therapy (NRT). The potential benefits of providing pregnant women with NRT to help them quit smoking are still unknown; early interventions to test the effectiveness and efficacy are vital to advancing the field. This paper describes recruitment efforts for a multiclinic trial to test the effectiveness of NRT use in addition to behavioral therapy in promoting cessation during pregnancy. The biggest challenge is recruiting sufficient numbers of pregnant women. This paper discusses specific obstacles for recruitment and solutions. Knowing the potential pitfalls to recruiting pregnant women into these trials can lead to better studies and thus improved outcomes. 相似文献
36.
Moser DP Fredrickson JK Geist DR Arntzen EV Peacock AD Li SM Spadoni T McKinley JP 《Environmental science & technology》2003,37(22):5127-5134
Biogeochemical processes within riverbed hyporheic zones (HZ) can potentially impact the fate and transport of contaminants. We evaluated a modified freeze core technique for the collection of intact cobble-bed samples from the Columbia River HZ along a stretch of the Hanford Reach in Washington State and investigated microbiological and geochemical parameters of corresponding frozen and unfrozen samples. During three sampling periods (March, May, and November 2000), relatively high numbers of viable aerobic heterotrophic bacteria were recovered from both unfrozen (10(6)-10(7) cfu/g) and frozen samples (10(5)-10(6) cfu/g). Relatively large populations of sulfate-, nitrate-, and iron-reducing bacteria were present, and significant concentrations of acid-volatile sulfide were measured in some samples, indicating that anoxic regions exist within this zone. Cr(VI), a priority groundwater pollutant on adjacent U.S. Department of Energy lands, was probably removed from solution in HZ samples by a combination of microbial activity and chemical reduction, presumably via products of anaerobic microbial metabolism. These results suggest that biogeochemical processes in the Columbia River HZ may contribute to the natural attenuation of Cr(VI). Although freezing modestly diminished recovery of viable bacteria, freeze core techniques proved reliable for the collection of intact hyporheic sediments. 相似文献
37.
The dissociation of protein ions formed by ESI ranging in size from 12 to 29 kDa using sustained off-resonance irradiation collisional activation was investigated as a function of charge state in a 9.4-T Fourier transform mass spectrometer. Addition of m-nitrobenzyl alcohol to denaturing solutions of proteins was used to form very high charge states of protein ions for these experiments. For all proteins in this study, activation of the highest charge state results in a single dominant backbone cleavage, often with less abundant cleavages at the neighboring 3-5 residues. This surprising phenomenon may be useful for the "top-down" identification of proteins by producing sequence tags with optimum sensitivity. There is a slight preference for cleavage adjacent to acidic residues and proline. Solution-phase secondary structure does not appear to play a significant role. The very limited dissociation channels observed for the supercharged ions may be due, in part, to the locations of the charges on the protein. 相似文献
38.
The Orientations of Large Aspect‐Ratio Coiled‐Coil Proteins Attached to Gold Nanostructures 下载免费PDF全文
Jae‐Byum Chang Yong Ho Kim Evan Thompson Young Hyun No Nam Hyeong Kim Jose Arrieta Vitor R. Manfrinato Amy E. Keating Karl K. Berggren 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(11):1498-1505
Methods for patterning biomolecules on a substrate at the single molecule level have been studied as a route to sensors with single‐molecular sensitivity or as a way to probe biological phenomena at the single‐molecule level. However, the arrangement and orientation of single biomolecules on substrates has been less investigated. Here, the arrangement and orientation of two rod‐like coiled‐coil proteins, cortexillin and tropomyosin, around patterned gold nanostructures is examined. The high aspect ratio of the coiled coils makes it possible to study their orientations and to pursue a strategy of protein orientation via two‐point attachment. The proteins are anchored to the surfaces using thiol groups, and the number of cysteine residues in tropomyosin is varied to test how this variation affects the structure and arrangement of the surface‐attached proteins. Molecular dynamics studies are used to interpret the observed positional distributions. Based on initial studies of protein attachment to gold post structures, two 31‐nm‐long tropomyosin molecules are aligned between the two sidewalls of a trench with a width of 68 nm. Because the approach presented in this study uses one of twenty natural amino acids, this method provides a convenient way to pattern biomolecules on substrates using standard chemistry. 相似文献
39.
The field of nanotechnology offers the possibility of transforming the international science and technology (S&T) policy landscape and making a significant impact on the direction of research and development for a wide range of nations and companies. Nanotechnology endeavors in the United States, China, and India remain some of the most interesting because of the opportunities and challenges this field poses for future competition and collaboration between these three nations. This paper examines how nanotechnology will raise new science and policy questions—and lead to new strategic linkages—that will have a major impact on the futures of these nations for decades to come. Then the paper analyzes and compares the current state of nanotechnology in these three countries, discusses some of the main drivers of collaboration, investigates current and potential uncertainties associated with nanotechnology, and offers policy suggestions on ways that these difficulties may be addressed. 相似文献
40.
Dbxtool is a window- and mouse-based debugger for C, Pascal and FORTRAN programs running on Sun workstations. Its use of the mouse as the primary input mechanism eliminates the need to type variables, line numbers, breakpoints and most commands. Its multiple windows provide several qualitatively different perspectives on the debugging problem. Compared to the Unix 4.2 BSD dbx from which it is derived, it has been extended with the abilities to debug multiple-process programs, already-running processes, and the Sun Operating System kernel. 相似文献