50,763 research outputs found
Study of a contractors capabilities center and the technology transfer process Final report, 15 Mar. 1966 - 30 Jun. 1968
Feasibility of NASA Contractors Capabilities Center, and approaches to technology utilizatio
Substituent effects on the nitrogen-15 and carbon-13 shieldings of some N-arylguanidinium chlorides
The 13C and 15N chemical shifts of five N-arylguanidinium chlorides carrying polar substituents, ranging in character from 4-methoxy to 4-nitro groups, have been determined by NMR spectroscopy at the natural-abundance level of 13C and 15N in dimethyl sulfoxide solution. Comparison of the 13C shifts of these salts with those of monosubstituted benzenes shows that the guanidinium group induces an average downfield shift of -5.8 ppm of the resonance of the aryl carbon to which it is attached (C1), an average upfield shift of +4.2 ppm for C2 and C6, and a small upfield shift of +1.9 ppm for C4. The shifts of C3 and C5 are small and erratic relative to the corresponding carbons in monosubstituted benzenes. The 15N resonances of the guanidinium nitrogens are quite sensitive to electric effects resulting from substitution of polar groups at C4. The 15N shift of the ==NAr nitrogen relative to that of the salts suggests that the predominant tautomer for N-arylguanidines is (H2N)2C==NAr. The 15N shifts of the (NH2) 2 nitrogens correlate rather well with σp- parameters, whereas the shifts of the -NHAr nitrogens seem to correlate only with R values derived from the σp- substituent constants
The role of follow-on contracts in government-sponsored research and development
Role of follow-on contracts in government sponsored research and developmen
Inviscid helical magnetorotational instability in cylindrical Taylor-Couette flow
This paper presents the analysis of axisymmetric helical magnetorotational
instability (HMRI) in the inviscid limit, which is relevant for astrophysical
conditions. The inductionless approximation defined by zero magnetic Prandtl
number is adopted to distinguish the HMRI from the standard MRI in the
cylindrical Taylor-Couette flow subject to a helical magnetic field. Using a
Chebyshev collocation method convective and absolute instability thresholds are
computed in terms of the Elsasser number for a fixed ratio of inner and outer
radii \lambda=2 and various ratios of rotation rates and helicities of the
magnetic field. It is found that the extension of self-sustained HMRI modes
beyond the Rayleigh limit does not reach the astrophysically relevant Keplerian
rotation profile not only in the narrow- but also in the finite-gap
approximation. The Keppler limit can be attained only by the convective HMRI
mode provided that the boundaries are perfectly conducting. However, this mode
requires not only a permanent external excitation to be observable but also has
a long axial wave length, which is not compatible with limited thickness of
astrophysical accretion disks.Comment: 12 pages, 9 figures, published version with a few typos correcte
Carbohydrate intake and cardiometabolic risk factors in high BMI African American children.
The aim of this study was to evaluate the relationship between intakes of subgroups of energy-providing carbohydrate, and markers of cardiometabolic risk factors in high BMI African American (AA) children.A cross sectional analysis was performed on data from a sample of 9-11 year old children (n = 95) with BMI greater than the 85th percentile. Fasting hematological and biochemical values for selected markers of cardiometabolic risk factors were related to intakes of carbohydrates and sugars.After adjusting for gender, pubertal stage and waist circumference, multivariate regression analysis showed that higher intakes of carbohydrate (with fat and protein held constant) were associated with higher plasma concentrations of triglycerides (TG), VLDL-C, IDL-C, and worse insulin resistance (homeostasis model assessment of insulin resistance, HOMA-IR). After dividing carbohydrate into non-sugar versus sugar fractions, sugars were significantly related to higher TG, VLDL-C, IDL-C, lower adipocyte fatty acid insulin sensitivity (ISI-FFA), and was closely associated with increased HOMA-IR. Similar trends were observed for sugars classified as added sugars, and for sugars included in beverages. Further dividing sugar according to the food group from which it was consumed showed that consuming more sugar from the candy/soda food group was highly significantly associated with increased TG, VLDL-C, IDL-C and closely associated with increased HOMA-IR. Sugars consumed in all fruit-containing foods were significantly associated with lower ISI-FFA. Sugars consumed as fruit beverages was significantly associated with VLDL-C, IDL-C and ISI-FFA whereas sugars consumed as fresh, dried and preserved fruits did not show significant associations with these markers.Sugars consumed from in all dairy foods were significantly associated with higher TG, VLDL-C and IDL-C, and with significantly lower HDL-C and ISI-FFA. These effects were associated with sugars consumed in sweetened dairy products, but not with sugars consumed in unsweetened dairy products. This analysis suggests that increases in carbohydrate energy, especially in the form of sugar, may be detrimental to cardiometabolic health in high BMI children
Extensive inventory of forest resources by multistage sampling
There are no author-identified significant results in this report
The use of high altitude, color and spectrozonal imagery for the inventory of wildland resources. Volume II - The range resource Annual progress report
High altitude multispectral imagery for identifying and mapping rangeland characteristic
Wilson Line Picture of Levin-Wen Partition Functions
Levin and Wen [Phys. Rev. B 71, 045110 (2005)] have recently given a lattice
Hamiltonian description of doubled Chern-Simons theories. We relate the
partition function of these theories to an expectation of Wilson loops that
form a link in 2+1 dimensional spacetime known in the mathematical literature
as Chain-Mail. This geometric construction gives physical interpretation of the
Levin-Wen Hilbert space and Hamiltonian, its topological invariance, exactness
under coarse-graining, and how two opposite chirality sectors of the doubled
theory arise.Comment: Final published version; Appendix adde
Effect of Different Types of Physical Activity on Activities of Daily Living in Older Adults : Systematic Review and Meta-Analysis
Peer reviewedPostprin
The Ekman-Hartmann layer in MHD Taylor-Couette flow
We study magnetic effects induced by rigidly rotating plates enclosing a
cylindrical MHD Taylor-Couette flow at the finite aspect ratio . The
fluid confined between the cylinders is assumed to be liquid metal
characterized by small magnetic Prandtl number, the cylinders are perfectly
conducting, an axial magnetic field is imposed \Ha \approx 10, the rotation
rates correspond to \Rey of order . We show that the end-plates
introduce, besides the well known Ekman circulation, similar magnetic effects
which arise for infinite, rotating plates, horizontally unbounded by any walls.
In particular there exists the Hartmann current which penetrates the fluid,
turns into the radial direction and together with the applied magnetic field
gives rise to a force. Consequently the flow can be compared with a Taylor-Dean
flow driven by an azimuthal pressure gradient. We analyze stability of such
flows and show that the currents induced by the plates can give rise to
instability for the considered parameters. When designing an MHD Taylor-Couette
experiment, a special care must be taken concerning the vertical magnetic
boundaries so they do not significantly alter the rotational profile.Comment: 9 pages, 6 figures; accepted to PR
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