6,871 research outputs found
Phosphorus in land-water systems
Analyses were made to obtain information on distribution of different forms of phosphate in different environmental media, including soils, eroding material, and bottom sediment. Major emphasis was placed on determining several forms of inorganic phosphate in each media. Results show that eroding material can transport significant quantities of phosphates from soils
The Fast Wandering of Slow Birds
I study a single "slow" bird moving with a flock of birds of a different, and
faster (or slower) species. I find that every "species" of flocker has a
characteristic speed , where is the mean speed of the
flock, such that, if the speed of the "slow" bird equals , it
will randomly wander transverse to the mean direction of flock motion far
faster than the other birds will: its mean-squared transverse displacement will
grow in with time like , in contrast to for the
other birds. In , the slow bird's mean squared transverse displacement
grows like , in contrast to for the other birds. If , the mean-squared displacement of the "slow" bird crosses over from
to scaling in , and from to scaling in
, at a time that scales according to .Comment: 10 pages; 5 pages of which did not appear in earlier versions, but
were added in response to referee's suggestion
A tow concept for the space shuttle orbiter approach and landing test
The tow concept provides the means for evaluating the orbiter aerodynamic performance and handling qualities in the same configuration as expected in actual space shuttle flight operation. A Boeing 747-100 aircraft has engine-out capability to tow the orbiter to an altitude that permits a safe orbiter approach and landing. The tow concept also provides a means for conducting a comprehensive ground test program before proceeding into the actual ALT flight operations. The implementation of the tow concept requires only a minor structural modification in the nose section of the orbiter vehicle; requires minor modifications in the 747 cargo bay; and makes use of those orbiter onboard systems installed in the ALT orbiter vehicle. The 747 wake turbulence does not constitute a problem for the orbiter during take-off or climb to altitude. The impact that the tow concept would have on the cost and schedule of the space shuttle program was not evaluated in this study
A study of wing body blending for an advanced supersonic transport
Increases in supersonic cruise lift drag ratio were sought at Mach numbers 2.2 and 2.7 using wing body planform and thickness blending. Constrained twist and camber optimization was performed in the presence of nacelles. Wing and fuselage thickness distributions were optimized for either minimum volume wave drag or minimum total pressure wave drag. The zero leading edge suction lift drag ratios were determined for three wing planforms. The magnitude of the effect of leading edge suction on attainable lift drag ratio was defined on one planform and estimation of available leading edge suction was made
Aircraft energy efficiency laminar flow control wing design study
An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft
A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks
I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find
new linear terms in the hydrodynamic equations which slightly modify the
anisotropy, but not the scaling, of the damping of sound modes. I also find
that the nonlinearities allowed {\it in equilibrium} do not stabilize long
ranged order in spatial dimensions ; in accord with the Mermin-Wagner
theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in
, as argued by earlier work. Some of these were missed by earlier work; it
is unclear whether or not they change the scaling exponents in .Comment: 6 pages, no figures. arXiv admin note: text overlap with
arXiv:0909.195
Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.Comment: To be published in PR
Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain
We investigate the finite-field ground state of the S=1
antiferromagnetic-ferromagnetic bond-alternating chain described by the
Hamiltonian
{\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell}
+J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell}
\bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z, where
\hbox{} and \hbox{}. We find that two kinds of
magnetization plateaux at a half of the saturation magnetization, the
1/2-plateaux, appear in the ground-state magnetization curve; one of them is of
the Haldane type and the other is of the large--type. We determine the
1/2-plateau phase diagram on the versus plane, applying the
twisted-boundary-condition level spectroscopy methods developed by Kitazawa and
Nomura. We also calculate the ground-state magnetization curves and the
magnetization phase diagrams by means of the density-matrix
renormalization-group method
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