2,783 research outputs found
Coronal Alfven waves and the solar wind
The observed properties of coronal Alfven waves in the solar wind at 1 AU are briefly reviewed, with some theoretical discussion of their probable effects on the dynamics of the expanding solar corona. It is concluded that coronal Alfven waves can have a major influence on both the small- and large-scale properties of the wind at 1 AU
Stellar winds driven by Alfven waves
Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds
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Inorganic nanowires
Provided in one embodiment is a method of forming an inorganic nanowire, comprising: providing an elongated organic scaffold; providing a plurality of inorganic nanoparticles attached to the organic scaffold along a length of the organic scaffold; and fusing the nanoparticles attached to the organic scaffold to form an inorganic nanowire.Board of Regents, University of Texas Syste
Cornell University remote sensing program
The major activities of the program staff from December 1, 1973 to May 31, 1974 are reported and include: (1) communication and instruction; (2) data and facilities; (3) research completed; (4) research in progress; (5) selected correspondence; (6) grant sponsored travel; and (7) seminars and newsletters. Detailed information and maps are given for the following selected projects: (1) ERTS mapping of waterways in the Tug Hill region of New York State; (2) photo-archeological investigation of Great Gully, New York; and (3) evaluation of selected highway impacts using aerial photography
Liquid immersion apparatus for minute articles
Apparatus is disclosed for immersing minute integrated circuit chips in an etching solution in manufacturing integrated circuits during research and development. The apparatus includes a holder, having a handle and basket support for carrying a removable unitary basket and lid structure where fluid flow-through passages are formed, and wherein graduated openings in the handle provide for adjustably supporting the basket in a breaker at a desired level
The Creation and Propagation of Radiation: Fields Inside and Outside of Sources
We present a new algorithm for computing the electromagnetic fields of
currents inside and outside of finite current sources, for arbitrary time
variations in the currents. Unexpectedly, we find that our solutions for these
fields are free of the concepts of differential calculus, in that our solutions
only involve the currents and their time integrals, and do not involve the time
derivatives of the currents. As examples, we give the solutions for two
configurations of current: a planar solenoid and a rotating spherical shell
carrying a uniform charge density. For slow time variations in the currents, we
show that our general solutions reduce to the standard expressions for the
fields in classic magnetic dipole radiation. In the limit of extremely fast
turn-on of the currents, we show that for our general solutions the amount of
energy radiated is exactly equal to the magnetic energy stored in the static
fields a long time after current creation. We give three associated problem
statements which can be used in courses at the undergraduate level, and one
problem statement suitable for courses at the graduate level. These problems
are of physical interest because: (1) they show that current systems of finite
extent can radiate even during time intervals when the currents are constant;
(2) they explicitly display transit time delays across a source associated with
its finite dimensions; and (3) they allow students to see directly the origin
of the reaction forces for time-varying systemsComment: 25 pages, 5 figure
Sunward-propagating Alfv\'enic fluctuations observed in the heliosphere
The mixture/interaction of anti-sunward-propagating Alfv\'enic fluctuations
(AFs) and sunward-propagating Alfv\'enic fluctuations (SAFs) is believed to
result in the decrease of the Alfv\'enicity of solar wind fluctuations with
increasing heliocentric distance. However, SAFs are rarely observed at 1 au and
solar wind AFs are found to be generally outward. Using the measurements from
Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere
inside 6 au. We first report two SAF events observed by Voyager 2. One is in
the anti-sunward magnetic sector with a strong positive correlation between the
fluctuations of magnetic field and solar wind velocity. The other one is in the
sunward magnetic sector with a strong negative magnetic field-velocity
correlation. Statistically, the percentage of SAFs increases gradually with
heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These
results provide new clues for understanding the generation mechanism of SAFs
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Viscous coupling of shear-free turbulence across nearly flat fluid interfaces
The interactions between shear-free turbulence in two regions (denoted as + and − on either side of a nearly flat horizontal interface are shown here to be controlled by several mechanisms, which depend on the magnitudes of the ratios of the densities, ρ+/ρ−, and kinematic viscosities of the fluids, μ+/μ−, and the root mean square (r.m.s.) velocities of the turbulence, u0+/u0−, above and below the interface. This study focuses on gas–liquid interfaces so that ρ+/ρ− ≪ 1 and also on where turbulence is generated either above or below the interface so that u0+/u0− is either very large or very small. It is assumed that vertical buoyancy forces across the interface are much larger than internal forces so that the interface is nearly flat, and coupling between turbulence on either side of the interface is determined by viscous stresses. A formal linearized rapid-distortion analysis with viscous effects is developed by extending the previous study by Hunt & Graham (J. Fluid Mech., vol. 84, 1978, pp. 209–235) of shear-free turbulence near rigid plane boundaries. The physical processes accounted for in our model include both the blocking effect of the interface on normal components of the turbulence and the viscous coupling of the horizontal field across thin interfacial viscous boundary layers. The horizontal divergence in the perturbation velocity field in the viscous layer drives weak inviscid irrotational velocity fluctuations outside the viscous boundary layers in a mechanism analogous to Ekman pumping. The analysis shows the following. (i) The blocking effects are similar to those near rigid boundaries on each side of the interface, but through the action of the thin viscous layers above and below the interface, the horizontal and vertical velocity components differ from those near a rigid surface and are correlated or anti-correlated respectively. (ii) Because of the growth of the viscous layers on either side of the interface, the ratio uI/u0, where uI is the r.m.s. of the interfacial velocity fluctuations and u0 the r.m.s. of the homogeneous turbulence far from the interface, does not vary with time. If the turbulence is driven in the lower layer with ρ+/ρ− ≪ 1 and u0+/u0− ≪ 1, then uI/u0− ~ 1 when Re (=u0−L−/ν−) ≫ 1 and R = (ρ−/ρ+)(v−/v+)1/2 ≫ 1. If the turbulence is driven in the upper layer with ρ+/ρ− ≪ 1 and u0+/u0− ≫ 1, then uI/u0+ ~ 1/(1 + R). (iii) Nonlinear effects become significant over periods greater than Lagrangian time scales. When turbulence is generated in the lower layer, and the Reynolds number is high enough, motions in the upper viscous layer are turbulent. The horizontal vorticity tends to decrease, and the vertical vorticity of the eddies dominates their asymptotic structure. When turbulence is generated in the upper layer, and the Reynolds number is less than about 106–107, the fluctuations in the viscous layer do not become turbulent. Nonlinear processes at the interface increase the ratio uI/u0+ for sheared or shear-free turbulence in the gas above its linear value of uI/u0+ ~ 1/(1 + R) to (ρ+/ρ−)1/2 ~ 1/30 for air–water interfaces. This estimate agrees with the direct numerical simulation results from Lombardi, De Angelis & Bannerjee (Phys. Fluids, vol. 8, no. 6, 1996, pp. 1643–1665). Because the linear viscous–inertial coupling mechanism is still significant, the eddy motions on either side of the interface have a similar horizontal structure, although their vertical structure differs
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