Recent Advances of the Forest in Iowa

At the time of settlement Iowa was definitely a prairie state with less than 20 per cent of its area covered by timber. Such a distribution of vegetation, coupled with short time observations, has led to the general assumption that prairie is the climax vegetation of the state. The writers have recently (7) assembled evidence that the present climate of Iowa is capable of supporting a forest climax. Prairie is therefore a subclimax associes maintained by its early establishment and by the marginal nature of the climate, but particularly by a combination of soil factors favoring prairie over woodland. The establishment of our classification depends upon evidence that forest is not only able to survive in Iowa, but that it has been able to invade the prairie at an appreciable rate under undisturbed conditions. Additional evidence of the spread of forest in Iowa, both after and before settlement, is presented here

Effects of light and soil moisture on forest tree seedling establishment

The present studies were designed to aid in the solution of forest tree seedling establishment problems common to stand conversion practices in Iowa. The primary objectives were: (1) to determine the minimum treatment needed to insure successful survival and growth; (2) to study the relationships of light and soil moisture in plant competition resulting from stand conversion; and (3) to evaluate five species of conifers - European larch, Scotch pine, eastern white pine, Norway spruce and red pine - for adaptability to region, site and underplanting. Field studies were made at the Brayton Forest in northeastern Iowa and consisted of ( 1 ) practical understory treatments to increase survival and growth of five underplanted conifers and (2) controlled experiments to evaluate overstory and understory competition in such plantings. Studies at the State Forest Nursery near Ames were planned to determine the relative growth and photosynthetic characteristics of three of the underplanted conifers (European larch, eastern white pine and Norway spruce) and two shrubby hardwood species ( dogwood and hazel) which offer serious understory competition in the forest

Locality and stability of the cascades of two-dimensional turbulence

We investigate and clarify the notion of locality as it pertains to the cascades of two-dimensional turbulence. The mathematical framework underlying our analysis is the infinite system of balance equations that govern the generalized unfused structure functions, first introduced by L'vov and Procaccia. As a point of departure we use a revised version of the system of hypotheses that was proposed by Frisch for three-dimensional turbulence. We show that both the enstrophy cascade and the inverse energy cascade are local in the sense of non-perturbative statistical locality. We also investigate the stability conditions for both cascades. We have shown that statistical stability with respect to forcing applies unconditionally for the inverse energy cascade. For the enstrophy cascade, statistical stability requires large-scale dissipation and a vanishing downscale energy dissipation. A careful discussion of the subtle notion of locality is given at the end of the paper.Comment: v2: 23 pages; 4 figures; minor revisions; resubmitted to Phys. Rev.

Classical and quantum regimes of the superfluid turbulence

We argue that turbulence in superfluids is governed by two dimensionless parameters. One of them is the intrinsic parameter q which characterizes the friction forces acting on a vortex moving with respect to the heat bath, with 1/q playing the same role as the Reynolds number Re=UR/\nu in classical hydrodynamics. It marks the transition between the "laminar" and turbulent regimes of vortex dynamics. The developed turbulence described by Kolmogorov cascade occurs when Re >> 1 in classical hydrodynamics, and q << 1 in the superfluid hydrodynamics. Another parameter of the superfluid turbulence is the superfluid Reynolds number Re_s=UR/\kappa, which contains the circulation quantum \kappa characterizing quantized vorticity in superfluids. This parameter may regulate the crossover or transition between two classes of superfluid turbulence: (i) the classical regime of Kolmogorov cascade where vortices are locally polarized and the quantization of vorticity is not important; and (ii) the quantum Vinen turbulence whose properties are determined by the quantization of vorticity. The phase diagram of the dynamical vortex states is suggested.Comment: 12 pages, 1 figure, version accepted in JETP Letter

The 4U 0115+63: Another energetic gamma ray binary pulsar

Following the discovery of Her X-1 as a source of pulsed 1000 Gev X-rays, a search for emission from an X-ray binary containing a pulsar with similar values of period, period derivative and luminosity was successful. The sporadic X-ray binary 4U 0115-63 has been observed, with probability 2.5 x 10 to the minus 6 power ergs/s to emit 1000 GeV gamma-rays with a time averaged energy flux of 6 to 10 to the 35th power

Fluctuating hydrodynamics and turbulence in a rotating fluid: Universal properties

We analyze the statistical properties of three-dimensional ($3d$) turbulence in a rotating fluid. To this end we introduce a generating functional to study the statistical properties of the velocity field $\bf v$. We obtain the master equation from the Navier-Stokes equation in a rotating frame and thence a set of exact hierarchical equations for the velocity structure functions for arbitrary angular velocity $\mathbf \Omega$. In particular we obtain the {\em differential forms} for the analogs of the well-known von Karman-Howarth relation for $3d$ fluid turbulence. We examine their behavior in the limit of large rotation. Our results clearly suggest dissimilar statistical behavior and scaling along directions parallel and perpendicular to $\mathbf \Omega$. The hierarchical relations yield strong evidence that the nature of the flows for large rotation is not identical to pure two-dimensional flows. To complement these results, by using an effective model in the small-$\Omega$ limit, within a one-loop approximation, we show that the equal-time correlation of the velocity components parallel to $\mathbf \Omega$ displays Kolmogorov scaling $q^{-5/3}$, where as for all other components, the equal-time correlators scale as $q^{-3}$ in the inertial range where $\bf q$ is a wavevector in $3d$. Our results are generally testable in experiments and/or direct numerical simulations of the Navier-Stokes equation in a rotating frame.Comment: 24 pages in preprint format; accepted for publication in Phys. Rev. E (2011