272 research outputs found
Exact thermodynamic Casimir forces for an interacting three-dimensional model system in film geometry with free surfaces
The limit n to infinity of the classical O(n) phi^4 model on a 3d film with
free surfaces is studied. Its exact solution involves a self-consistent 1d
Schr\"odinger equation, which is solved numerically for a partially discretized
as well as for a fully discrete lattice model. Numerically exact results are
obtained for the scaled Casimir force at all temperatures. Obtained via a
single framework, they exhibit all relevant qualitative features of the
thermodynamic Casimir force known from wetting experiments on Helium-4 and
Monte Carlo simulations, including a pronounced minimum below the bulk critical
point.Comment: 5 pages, 2 figure
Nutrient-Dense Orange-Fleshed Sweetpotato: Advances in Drought-Tolerance Breeding and Understanding of Management Practices for Sustainable Next-Generation Cropping Systems in Sub-Saharan Africa
Almost half of children < 5 years old living in sub-Saharan Africa (SSA) suffer from vitamin A deficiency and 60% suffer from iron deficiency. Thus, there has been a strong
commitment to breeding for, promoting awareness of, and delivering adapted pro-vitamin A rich orange-fleshed sweetpotato (OFSP) in SSA during the past two decades and
for enhanced iron content since 2014. This review article focuses on major breeding efforts in SSA to enhance the drought tolerance of OFSP and reviews integrated crop
management practices for improved and sustained sweetpotato production in SSA farming systems. Under climate change, the frequency and severity of droughts is expected to increase. Technical issues are presented in the context of addressing challenges along the entire value chain to ensure adoption. First, the use of an accelerated breeding scheme reduced the breeding cycle from 8–10 to 4–5 years.
Since 2010, 19 drought-tolerant OFSP cultivars have been released in Mozambique, 7 in Malawi, and 2 in South Africa. Moreover, research in four breeding populations
using the heterosis exploiting breeding scheme (HEBS) demonstrated that within one breeding cycle of 5 years, clones with significantly higher root yield, abiotic tolerance, host plant resistance to pests and diseases, and early maturity can be produced. In the future, HEBS will be combined with greater use of modern genomic tools,
new phenotyping tools, and CRISPR/Cas9-mediated gene editing. Second, beyond genetic enhancements, evidence is presented that using improved crop management
systems, existing sweet potato yields can be increased 2–4 times. Current knowledge is reviewed concerning sweetpotato’s role in diverse farming systems, but integrated crop management is clearly under researched. Third, the outlook for drought tolerance breeding indicates that two distinct classes of nutrient-rich cultivars are emerging: (1) Early maturing cultivars (< 4 month growing period) that escape drought but also serve humid environments with small landholding size per capita; and (2) Medium maturing (4–6 month growing period) cultivars that avoid drought, are drought tolerant and exhibit
continuous root formation. Increasing commercialization of the crop and climate change will drive demand, and the willingness of farmers to invest in improved sweetpotato
crop management
Test of Lorentz Symmetry by using a 3He/129Xe Co-Magnetometer
To test Lorentz symmetry we used a 3He/129Xe co-magnetometer. We will give a
short summary of our experimental setup and the results of our latest
measurements. We obtained preliminary results for the equatorial component of
the background field interacting with the spin of the bound neutron: b_n < 3.72
x 10^(-32) GeV (95 C.L.).Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28 - July 2, 201
Limit on Lorentz and CPT violation of the bound Neutron Using a Free Precession 3He/129Xe co-magnetometer
We report on the search for Lorentz violating sidereal variations of the
frequency difference of co-located spin-species while the Earth and hence the
laboratory reference frame rotates with respect to a relic background field.
The co-magnetometer used is based on the detection of freely precessing nuclear
spins from polarized 3He and 129Xe gas samples using SQUIDs as low-noise
magnetic flux detectors. As result we can determine the limit for the
equatorial component of the background field interacting with the spin of the
bound neutron to be bn < 3.7 x 10^{-32} GeV (95 C.L.).Comment: 5 pages, 4 figure
Thermodynamic Casimir effects involving interacting field theories with zero modes
Systems with an O(n) symmetrical Hamiltonian are considered in a
-dimensional slab geometry of macroscopic lateral extension and finite
thickness that undergo a continuous bulk phase transition in the limit
. The effective forces induced by thermal fluctuations at and above
the bulk critical temperature (thermodynamic Casimir effect) are
investigated below the upper critical dimension by means of
field-theoretic renormalization group methods for the case of periodic and
special-special boundary conditions, where the latter correspond to the
critical enhancement of the surface interactions on both boundary planes. As
shown previously [\textit{Europhys. Lett.} \textbf{75}, 241 (2006)], the zero
modes that are present in Landau theory at make conventional
RG-improved perturbation theory in dimensions ill-defined. The
revised expansion introduced there is utilized to compute the scaling functions
of the excess free energy and the Casimir force for temperatures
T\geqT_{c,\infty} as functions of , where
is the bulk correlation length. Scaling functions of the
-dependent residual free energy per area are obtained whose
limits are in conformity with previous results for the Casimir amplitudes
to and display a more reasonable
small- behavior inasmuch as they approach the critical value
monotonically as .Comment: 23 pages, 10 figure
Excess free energy and Casimir forces in systems with long-range interactions of van-der-Waals type: General considerations and exact spherical-model results
We consider systems confined to a -dimensional slab of macroscopic lateral
extension and finite thickness that undergo a continuous bulk phase
transition in the limit and are describable by an O(n) symmetrical
Hamiltonian. Periodic boundary conditions are applied across the slab. We study
the effects of long-range pair interactions whose potential decays as as , with and , on
the Casimir effect at and near the bulk critical temperature ,
for . For the scaled reduced Casimir force per unit cross-sectional
area, we obtain the form L^{d} {\mathcal F}_C/k_BT \approx \Xi_0(L/\xi_\infty)
+ g_\omega L^{-\omega}\Xi\omega(L/\xi_\infty) + g_\sigma L^{-\omega_\sigm a}
\Xi_\sigma(L \xi_\infty). The contribution decays for
algebraically in rather than exponentially, and hence
becomes dominant in an appropriate regime of temperatures and . We derive
exact results for spherical and Gaussian models which confirm these findings.
In the case , which includes that of nonretarded van-der-Waals
interactions in dimensions, the power laws of the corrections to scaling
of the spherical model are found to get modified by logarithms.
Using general RG ideas, we show that these logarithmic singularities originate
from the degeneracy that occurs for the spherical
model when , in conjunction with the dependence of .Comment: 28 RevTeX pages, 12 eps figures, submitted to PR
Ultra-sensitive magnetometry based on free precession of nuclear spins
We discuss the design and performance of a very sensitive low-field
magnetometer based on the detection of free spin precession of gaseous, nuclear
polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. The
device will be employed to control fluctuating magnetic fields and gradients in
a new experiment searching for a permanent electric dipole moment of the
neutron as well as in a new type of 3He/129Xe clock comparison experiment which
should be sensitive to a sidereal variation of the relative spin precession
frequency. Characteristic spin precession times T_2 of up to 60h could be
measured. In combination with a signal-to-noise ratio of > 5000:1, this leads
to a sensitivity level of deltaB= 1fT after an integration time of 220s and to
deltaB= 10^(-4)fT after one day. Even in that sensitivity range, the
magnetometer performance is statistically limited, and noise sources inherent
to the magnetometer are not limiting. The reason is that free precessing 3He
(129Xe) nuclear spins are almost completely decoupled from the environment.
That makes this type of magnetometer in particular attractive for precision
field measurements where a long-term stability is required
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