99,209 research outputs found
Sulfofication in soils
Sulfur has long been known to be one of the essential plant food constituents. It has always been believed, however, that there was sufficient present in all soils for the optimum growth of crops. This assumption has been very largely based on Wolff\u27s analyses of the ashes of various crops which showed the presence of very small amounts of sulfur.
The recent work of many investigators has demonstrated, however, that the amount of sulfur in plant materials as determined in the ash is, in most cases, entirely too low; that there is a considerable loss of sulfur in the process of igniting; and that the amount found in the ash may therefore be a very small part of that originally present in the plant tissue
Sulfofication in Soils
Sulfur has long been known to be one of the essential plant food constituents. It has always been believed, however, that there was sufficient present in all soils for optimum crop production. This assumption has been very largely based on Wolff’s analyses of the ash of various crops which showed the presence of very small amounts of sulfur. Several investigators have found a considerable loss of sulfur upon ignition of plants for ash determinations, and recently Hart and Peterson, of Wisconsin, pointed out definitely the inaccuracy of determining the total sulfur of plant tissues by examinations of the ash. They analyzed numerous feeding stuffs for total sulfur, using the Osborn method, and compared their results with the earlier analyses of Wolff. This comparison showed quite conclusively that a large proportion of the sulfur in crops is lost upon ignition. It is evident, therefore, that considerably larger amounts of sulfur are removed from soils by common farm crops than has been supposed
Branching of the Falkner-Skan solutions for λ < 0
The Falkner-Skan equation f'" + ff" + λ(1 - f'^2) = 0, f(0) = f'(0) = 0, is discussed for λ < 0. Two types of problems, one with f'(∞) = 1 and another with f'(∞) = -1, are considered. For λ = 0- a close relation between these two types is found. For λ < -1 both types of problem allow multiple solutions which may be distinguished by an integer N denoting the number of zeros of f' - 1. The numerical results indicate that the solution branches with f'(∞) = 1 and those with f'(∞) = -1 tend towards a common limit curve as N increases indefinitely. Finally a periodic solution, existing for λ < -1, is presented.
The chameleon groups of Richard J. Thompson: automorphisms and dynamics
The automorphism groups of several of Thompson's countable groups of
piecewise linear homeomorphisms of the line and circle are computed and it is
shown that the outer automorphism groups of these groups are relatively small.
These results can be interpreted as stability results for certain structures of
PL functions on the circle. Machinery is developed to relate the structures on
the circle to corresponding structures on the line
Universal measurement of quantum correlations of radiation
A measurement technique is proposed which, in principle, allows one to
observe the general space-time correlation properties of a quantized radiation
field. Our method, called balanced homodyne correlation measurement, unifies
the advantages of balanced homodyne detection with those of homodyne
correlation measurements.Comment: 4 pages, 4 figures, small misprints were corrected, accepted to Phys.
Rev. Let
Time-Reversal-Violating Schiff Moment of 199Hg
We calculate the Schiff moment of the nucleus 199Hg, created by pi-N-N
vertices that are odd under parity (P) and time-reversal (T). Our approach,
formulated in diagrammatic perturbation theory with important core-polarization
diagrams summed to all orders, gives a close approximation to the expectation
value of the Schiff operator in the odd-A Hartree-Fock-Bogoliubov ground state
generated by a Skyrme interaction and a weak P- and T-odd pion-exchange
potential. To assess the uncertainty in the results, we carry out the
calculation with several Skyrme interactions (the quality of which we test by
checking predictions for the isoscalar-E1 strength distribution in 208Pb) and
estimate most of the important diagrams we omit.Comment: 13 pages, 7 figure
Field Quantization, Photons and Non-Hermitean Modes
Field quantization in three dimensional unstable optical systems is treated
by expanding the vector potential in terms of non-Hermitean (Fox-Li) modes in
both the cavity and external regions. The cavity non-Hermitean modes (NHM) are
treated using the paraxial and monochromaticity approximations. The NHM
bi-orthogonality relationships are used in a standard canonical quantization
procedure based on introducing generalised coordinates and momenta for the
electromagnetic (EM) field. The quantum EM field is equivalent to a set of
quantum harmonic oscillators (QHO), associated with either the cavity or the
external region NHM. This confirms the validity of the photon model in unstable
optical systems, though the annihilation and creation operators for each QHO
are not Hermitean adjoints. The quantum Hamiltonian for the EM field is the sum
of non-commuting cavity and external region contributions, each of which is sum
of independent QHO Hamiltonians for each NHM, but the external field
Hamiltonian also includes a coupling term responsible for external NHM photon
exchange processes. Cavity energy gain and loss processes is associated with
the non-commutativity of cavity and external region operators, given in terms
of surface integrals involving cavity and external region NHM functions on the
cavity-external region boundary. The spontaneous decay of a two-level atom
inside an unstable cavity is treated using the essential states approach and
the rotating wave approximation. Atomic transitions leading to cavity NHM
photon absorption have a different coupling constant to those leading to photon
emission, a feature resulting from the use of NHM functions. Under certain
conditions the decay rate is enhanced by the Petermann factor.Comment: 38 pages, tex, 2 figures, ps. General expression for decay rate
added. To be published in Journal of Modern Optic
3D mapping of young stars in the solar neighbourhood with Gaia DR2
We study the three dimensional arrangement of young stars in the solar
neighbourhood using the second release of the Gaia mission (Gaia DR2) and we
provide a new, original view of the spatial configuration of the star forming
regions within 500 pc from the Sun. By smoothing the star distribution through
a gaussian filter, we construct three dimensional density maps for early-type
stars (upper-main sequence, UMS) and pre-main sequence (PMS) sources. The PMS
and the UMS samples are selected through a combination of photometric and
astrometric criteria. A side product of the analysis is a three dimensional,
G-band extinction map, which we use to correct our colour-magnitude diagram for
extinction and reddening. Both density maps show three prominent structures,
Scorpius-Centaurus, Orion, and Vela. The PMS map shows a plethora of lower mass
star forming regions, such as Taurus, Perseus, Cepheus, Cassiopeia, and
Lacerta, which are less visible in the UMS map, due to the lack of large
numbers of bright, early-type stars. We report the finding of a candidate new
open cluster towards , which could be
related to the Orion star forming complex. We estimate ages for the PMS sample
and we study the distribution of PMS stars as a function of their age. We find
that younger stars cluster in dense, compact clumps, and are surrounded by
older sources, whose distribution is instead more diffuse. The youngest groups
that we find are mainly located in Scorpius-Centaurus, Orion, Vela, and Taurus.
Cepheus, Cassiopeia, and Lacerta are instead more evolved and less numerous.
Finally, we find that the three dimensional density maps show no evidence for
the existence of the ring-like structure which is usually referred to as the
Gould Belt.Comment: 17 pages, 17 figures, 6 appendixes; accepted for publication in A&A;
image quality decreased to comply with the arXiv.org rules on file siz
Soil Survey of Iowa, Report No. 59—Cherokee County Soils
Cherokee County is located in the northwestern part of the state, in the third tier of counties south of the Minnesota state line and in the second tier east of the South Dakota state line. It lies mainly in the Missouri loess soil area and hence the soils of the county are largely of loessial origin
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