3,328 research outputs found
Response of cottonseed to direct-current glow discharge
This study was conducted to determine the effects of direct-current glow-discharge treatment, current intensity, exposure time, and energy generated during treatment on the early and total germination of Empire ÂĄR cottonseed. Germination counts were made at 2, 3j hf and 12 days. Three Minute glow-discharge treatments at 30^150 milliamperes and 6-minute treatments at 30~95 milliamperes significantly improved early germination. Current intensities of 100-1^0 milliamperes for 6 minutes decreased both early and total germination. Multiple regression was calculated using p germination as the dependent variable and energy, energy2, seed temperature, seed temperature2, moisture loss during treatment, and moisture loss2 as the independent variables. In this regression the coefficient of determination for energy and energy2 accounted for 91 percent of the variability in early germination and 92 percent of the variability in total germination
Optimum site selection for blacklight insect traps as predicted by relating tobacco hornworm collections to factors describing trap surroundings
Seventy parameters describing surroundings of 51 blacklight insect trap locations on St. Croix, U. S. Virgin Islands were related to insect categories of male, mated female, virgin female, total tobacco hornworm (Manduca sexta), and the white belly (M. sexta harterti). Data were obtained from an on-site survey pertaining to slope of land at trap site, deviation of slopes from prevailing wind, roadways, incident light, slope to obstruction, and distance from traps to obstructions. Obtained from descriptive data of locations were trap density, distance from shorelines, elevation above sea level, slope of land in vicinity of traps, deviation of slope in vicinity of traps from prevailing wind, land-use category, vegetation type, geology type, groundwater potential yield, groundwater chloride, soil limitations to agriculture or development, soil association, and soil capability class.
Significance of relationships between insect collections and criteria was determined by analysis of variance for 14 discrete factors, and by correlation and multiple regression analyses for the continuous factors. Criteria significantly related to collections five or more times were type of obstruction, slope to obstruction, distance to obstruction, distance to shoreline, soil limitations to agriculture and development, slope of trap site, slope of trap vicinity, and deviation of slope in vicinity of traps from prevailing wind.
Significant one to four times were vegetation type, geology type, soil association, distance to roadway, related traffic flow on roadway, weighted obstruction, percent obstruction, land-use category scaled according to estimated ability to support an insect population, slope deviation at site from prevailing wind, groundwater potential yield, soil capability class, relative ultraviolet radiation of incident light, relative intensity of incident light, elevation of trap site, and trap density
Statistics on Graphs, Exponential Formula and Combinatorial Physics
The concern of this paper is a famous combinatorial formula known under the
name "exponential formula". It occurs quite naturally in many contexts
(physics, mathematics, computer science). Roughly speaking, it expresses that
the exponential generating function of a whole structure is equal to the
exponential of those of connected substructures. Keeping this descriptive
statement as a guideline, we develop a general framework to handle many
different situations in which the exponential formula can be applied
Reversible strain effect on the magnetization of LaCoO3 films
The magnetization of ferromagnetic LaCoO3 films grown epitaxially on
piezoelectric substrates has been found to systematically decrease with the
reduction of tensile strain. The magnetization change induced by the reversible
strain variation reveals an increase of the Co magnetic moment with tensile
strain. The biaxial strain dependence of the Curie temperature is estimated to
be below 4K/% in the as-grown tensile strain state of our films. This is in
agreement with results from statically strained films on various substrates
Spin-state transition and spin-polaron physics in cobalt oxide perovskites: ab initio approach based on quantum chemical methods
A fully ab initio scheme based on quantum chemical wavefunction methods is
used to investigate the correlated multiorbital electronic structure of a
3d-metal compound, LaCoO3. The strong short-range electron correlations,
involving both Co and O orbitals, are treated by multireference techniques. The
use of effective parameters like the Hubbard U and interorbital U', J terms and
the problems associated with their explicit calculation are avoided with this
approach. We provide new insight into the spin-state transition at about 90 K
and the nature of charge carriers in the doped material. Our results indicate
the formation of a t4e2 high-spin state in LaCoO3 for T>90 K. Additionally, we
explain the paramagnetic phase in the low-temperature lightly doped compound
through the formation of Zhang-Rice-like O hole states and ferromagnetic
clusters
Pressure effects on the magnetic structure in La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites
The effect of high pressure (0 - 8 GPa) on the magnetic structure of
polycrystalline samples of La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites at
5 K is investigated using neutron diffraction technique. Application of
pressure is found to modify the previously reported magnetic structure,
observed under ambient conditions, in these compounds [I. Dhiman et al., Phys.
Rev. B 77, 094440 (2008)]. In x = 0.1 composition, at 4.6(2) GPa and beyond,
A-type antiferromagnetic structure is found to coexist with CE-type
antiferromagnetic phase, observed at ambient pressure, with TN ~ 150 K. For x =
0.3 sample, as a function of pressure the CE-type phase is fully suppressed at
2.3(1) GPa and A-type antiferromagnetic phase is favored. Further Sr doping at
x = 0.4, the A-type antiferromagnetic phase is observed at ambient pressure and
for T < TN (~ 250K). This phase is retained in the studied pressure range.
However, the magnetic moment progressively reduces with increasing pressure,
indicating the suppression of A-type antiferromagnetic phase. The present study
brings out the fragile nature of the CE-type antiferromagnetic state in half
doped manganites as a function of pressure and disorder \sigma 2. We observe
that pressure required for destabilizing the CE-type antiferromagnetic state is
reduced with increasing disorder \sigma 2. External pressure and changing
A-site ionic radii have analogous effect on the magnetic structure.Comment: 9 pages, 6 figures, 1 table, To appear in Physical Review
Electric-field control of magnetic ordering in the tetragonal BiFeO3
We propose a way to use electric-field to control the magnetic ordering of
the tetragonal BiFeO3. Based on systematic first-principles studies of the
epitaxial strain effect on the ferroelectric and magnetic properties of the
tetragonal BiFeO3, we find that there exists a transition from C-type to G-type
antiferromagnetic (AFM) phase at in-plane constant a ~ 3.905 {\AA} when the
ferroelectric polarization is along [001] direction. Such magnetic phase
transition can be explained by the competition between the Heisenberg exchange
constant J1c and J2c under the influence of biaxial strain. Interestingly, when
the in-plane lattice constant enlarges, the preferred ferroelectric
polarization tends to be canted and eventually lies in the plane (along [110]
direction). It is found that the orientation change of ferroelectric
polarization, which can be realized by applying external electric-field, has
significant impact on the Heisenberg exchange parameters and therefore the
magnetic orderings of tetragonal BiFeO3. For example, at a ~ 3.79 {\AA}, an
electric field along [111] direction with magnitude of 2 MV/cm could change the
magnetic ordering from C-AFM to G-AFM. As the magnetic ordering affects many
physical properties of the magnetic material, e.g. magnetoresistance, we expect
such strategy would provide a new avenue to the application of multiferroic
materials.Comment: 4 pages, 4 figure
Phase Competition in Ln0.5a0.5mno3 Perovskites
Single crystals of the systems Pr0.5(Ca1-xSrx)0.5MnO3,
(Pr1-yYy)0.5(Ca1-xSrx)0.5MnO3, and Sm0.5Sr0.5MnO3 were grown to provide a
series of samples with fixed ratio Mn(III)/Mn(IV)=1 having geometric tolerance
factors that span the transition from localized to itinerant electronic
behavior of the MnO3 array. A unique ferromagnetic phase appears at the
critical tolerance factor tc= 0.975 that separates charge ordering and
localized-electron behavior for t<tc from itinerant or molecular-orbital
behavior for t>tc. This ferromagnetic phase, which has to be distinguished from
the ferromagnetic metallic phase stabilized at tolerance factors t>tc,
separates two distinguishable Type-CE antiferromagnetic phases that are
metamagnetic. Measurements of the transport properties under hydrostatic
pressure were carried out on a compositions t a little below tc in order to
compare the effects of chemical vs. hydrostatic pressure on the phases that
compete with one another near t=tc.Comment: 10 pages. To be publised in Phys. Rev.
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