200 research outputs found
Common names of weeds in Missouri field crops
"Common weeds in field crops are known by at least two common names; some by a dozen or more. For example, Abutilon theophrasti may be referred to as wild cotton in southeast Missouri, while farmers in a northwest community may call it butter print. Indian mallow might be the preferred name in another locale. But if you want to use the name that will get the most nods of recognition from farmers throughout this country, call it velvetleaf. The many common names of weeds frequently creates communication problems. During a conversation, two people may refer to a plant species, but use different common names. They don't realize that they are both referring to the same plant. More importantly, this confusion can result in erroneous weed management decisions."--First page.William W. Dierker and Mitchell E. Roof (Integrated Pest Management College of Agriculture)New 8/82/8
Weed competition in soybeans and corn
"6/82/1M""The effects of weed competition on crop yields demonstrate the importance of weed control practices. This review of weed competition focuses on crops that are economically important to Missouri."--first paragraphUniversity of Missouri Extension DivisionIncludes bibliographical reference
Domain Growth, Wetting and Scaling in Porous Media
The lattice Boltzmann (LB) method is used to study the kinetics of domain
growth of a binary fluid in a number of geometries modeling porous media.
Unlike the traditional methods which solve the Cahn-Hilliard equation, the LB
method correctly simulates fluid properties, phase segregation, interface
dynamics and wetting. Our results, based on lattice sizes of up to , do not show evidence to indicate the breakdown of late stage dynamical
scaling, and suggest that confinement of the fluid is the key to the slow
kinetics observed. Randomness of the pore structure appears unnecessary.Comment: 13 pages, latex, submitted to PR
Effects of pressure on spin fluctuations and the exchange interaction in La2CuO4 as determined by two‐magnon Raman scattering (abstract)
We have measured the two‐magnon Raman scattering spectrum of magnetic La2CuO4 at pressures of up to 100 kbar. Analysis of the moments of the two‐magnon line shape indicates that the renormalization parameters resulting from spin fluctuations are essentially pressure independent in this pressure range. Our results provide the first direct determination of the pressure dependence of the in‐plane exchange coupling constant J. The pressure dependence of J is compared with that of the Néel temperature and discussed in the context of recent theories for quasi‐two‐dimensional magnetic systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71024/2/JAPIAU-69-8-5392-1.pd
Rigid Chiral Membranes
Statistical ensembles of flexible two-dimensional fluid membranes arise
naturally in the description of many physical systems. Typically one encounters
such systems in a regime of low tension but high stiffness against bending,
which is just the opposite of the regime described by the Polyakov string. We
study a class of couplings between membrane shape and in-plane order which
break 3-space parity invariance. Remarkably there is only {\it one} such
allowed coupling (up to boundary terms); this term will be present for any
lipid bilayer composed of tilted chiral molecules. We calculate the
renormalization-group behavior of this relevant coupling in a simplified model
and show how thermal fluctuations effectively reduce it in the infrared.Comment: 11 pages, UPR-518T (This replaced version has fonts not used
removed.
Observation of the Smectic C -- Smectic I Critical Point
We report the first observation of the smectic C--smectic I (C--I) critical
point by Xray diffraction studies on a binary system. This is in confirmity
with the theoretical idea of Nelson and Halperin that coupling to the molecular
tilt should induce hexatic order even in the C phase and as such both C and I
(a tilted hexatic phase) should have the same symmetry. The results provide
evidence in support of the recent theory of Defontaines and Prost proposing a
new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from
[email protected] on request, Phys.Rev.Lett. (in press
On the origin of the A and B electronic Raman scattering peaks in the superconducting state of YBaCuO
The electronic Raman scattering has been investigated in optimally oxygen
doped YBaCuO single crystals as well as in crystals
with non-magnetic, Zn, and magnetic, Ni, impurities. We found that the
intensity of the A peak is impurity independent and their energy to
ratio is almost constant (). Moreover, the
signal at the B channel is completely smeared out when non-magnetic Zn
impurities are present. These results are qualitatively interpreted in terms of
the Zeyher and Greco's theory that relates the electronic Raman scattering in
the A and B channels to \textit{d}-CDW and superconducting order
parameters fluctuations, respectively.Comment: Submited to Phys. Rev. Let
A study of the superconducting gap in RNiBC (R = Y, Lu) single crystals by inelastic light scattering
Superconductivity-induced changes in the electronic Raman scattering response
were observed for the RNiBC (R = Y, Lu) system in different scattering
geometries. In the superconducting state, 2-like peaks were observed in
A, B, and B spectra from single crystals. The peaks in
A and B symmetries are significantly sharper and stronger than
the peak in B symmetry. The temperature dependence of the frequencies of
the 2-like peaks shows typical BCS-type behavior, but the apparent
values of the gap are strongly anisotropic for both systems. In
addition, for both YNiBC and LuNiBC systems, there exists
reproducible scattering strength below the gap which is roughly
linear to the frequency in B and B symmetries. This discovery of
scattering below the gap in non-magnetic borocarbide superconductors, which are
thought to be conventional BCS-type superconductors, is a challenge for current
understanding of superconductivity in this system.Comment: Added text, changed a figure, and added references. Will appear in
Phys. Rev.
Evolution of speckle during spinodal decomposition
Time-dependent properties of the speckled intensity patterns created by
scattering coherent radiation from materials undergoing spinodal decomposition
are investigated by numerical integration of the Cahn-Hilliard-Cook equation.
For binary systems which obey a local conservation law, the characteristic
domain size is known to grow in time as with n=1/3,
where B is a constant. The intensities of individual speckles are found to be
nonstationary, persistent time series. The two-time intensity covariance at
wave vector can be collapsed onto a scaling function , where and . Both analytically and numerically, the covariance
is found to depend on only through in the
small- limit and in the large-
limit, consistent with a simple theory of moving interfaces that applies to any
universality class described by a scalar order parameter. The speckle-intensity
covariance is numerically demonstrated to be equal to the square of the
two-time structure factor of the scattering material, for which an analytic
scaling function is obtained for large In addition, the two-time,
two-point order-parameter correlation function is found to scale as
, even for quite large
distances . The asymptotic power-law exponent for the autocorrelation
function is found to be , violating an upper bound
conjectured by Fisher and Huse.Comment: RevTex: 11 pages + 12 figures, submitted to PR
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