Reduced Scepter Rates for Broadleaf Weed Control in Soybean

Public agencies are placing greater scrutiny on herbicide applications by farmers. For example, the corn herbicide atrazine is now classified as a restricted use pesticide, with limits placed on allowable rates. While soybean growers may share some of this concern for the environment, rate reduction is more likely to be attractive for economic reasons. Some growers are already cutting back on herbicide rates. For example, Missouri data shows that the average application rates for soybean herbicides were only 75% of the labelled rate. While reduced rates might save growers money, and may be kinder to the environment, there is a concern that poorer weed control could show up under unfavorable conditions

2D Cine DENSE with Low Encoding Frequencies Accurately Quantifies Cardiac Mechanics with Improved Image Characteristics

BACKGROUND: Displacement Encoding with Stimulated Echoes (DENSE) encodes displacement into the phase of the magnetic resonance signal. The encoding frequency (ke) maps the measured phase to tissue displacement while the strength of the encoding gradients affects image quality. 2D cine DENSE studies have used a ke of 0.10 cycles/mm, which is high enough to remove an artifact-generating echo from k-space, provide high sensitivity to tissue displacements, and dephase the blood pool. However, through-plane dephasing can remove the unwanted echo and dephase the blood pool without relying on high ke. Additionally, the high sensitivity comes with the costs of increased phase wrapping and intra-voxel dephasing. We hypothesized that ke below 0.10 cycles/mm can be used to improve image characteristics and provide accurate measures of cardiac mechanics. METHODS: Spiral cine DENSE images were obtained for 10 healthy subjects and 10 patients with a history of heart disease on a 3 T Siemens Trio. A mid-ventricular short-axis image was acquired with different ke: 0.02, 0.04, 0.06, 0.08, and 0.10 cycles/mm. Peak twist, circumferential strain, and radial strain were compared between acquisitions employing different ke using Bland-Altman analyses and coefficients of variation. The percentage of wrapped pixels in the phase images at end-systole was calculated for each ke. The dephasing of the blood signal and signal to noise ratio (SNR) were also calculated and compared. RESULTS: Negligible differences were seen in strains and twist for all ke between 0.04 and 0.10 cycles/mm. These differences were of the same magnitude as inter-test differences. Specifically, the acquisitions with 0.04 cycles/mm accurately quantified cardiac mechanics and had zero phase wrapping. Compared to 0.10 cycles/mm, the acquisitions with 0.04 cycles/mm had 9 % greater SNR and negligible differences in blood pool dephasing. CONCLUSIONS: For 2D cine DENSE with through-plane dephasing, the encoding frequency can be lowered to 0.04 cycles/mm without compromising the quantification of twist or strain. The amount of wrapping can be reduced with this lower value to greatly simplify the input to unwrapping algorithms. The strain and twist results from studies using different encoding frequencies can be directly compared

Validation of \u3cem\u3eIn Vivo\u3c/em\u3e 2D Displacements from Spiral Cine DENSE at 3T

BACKGROUND: Displacement Encoding with Stimulated Echoes (DENSE) encodes displacement into the phase of the magnetic resonance signal. Due to the stimulated echo, the signal is inherently low and fades through the cardiac cycle. To compensate, a spiral acquisition has been used at 1.5T. This spiral sequence has not been validated at 3T, where the increased signal would be valuable, but field inhomogeneities may result in measurement errors. We hypothesized that spiral cine DENSE is valid at 3T and tested this hypothesis by measuring displacement errors at both 1.5T and 3T in vivo. METHODS: Two-dimensional spiral cine DENSE and tagged imaging of the left ventricle were performed on ten healthy subjects at 3T and six healthy subjects at 1.5T. Intersection points were identified on tagged images near end-systole. Displacements from the DENSE images were used to project those points back to their origins. The deviation from a perfect grid was used as a measure of accuracy and quantified as root-mean-squared error. This measure was compared between 3T and 1.5T with the Wilcoxon rank sum test. Inter-observer variability of strains and torsion quantified by DENSE and agreement between DENSE and harmonic phase (HARP) were assessed by Bland-Altman analyses. The signal to noise ratio (SNR) at each cardiac phase was compared between 3T and 1.5T with the Wilcoxon rank sum test. RESULTS: The displacement accuracy of spiral cine DENSE was not different between 3T and 1.5T (1.2 ± 0.3 mm and 1.2 ± 0.4 mm, respectively). Both values were lower than the DENSE pixel spacing of 2.8 mm. There were no substantial differences in inter-observer variability of DENSE or agreement of DENSE and HARP between 3T and 1.5T. Relative to 1.5T, the SNR at 3T was greater by a factor of 1.4 ± 0.3. CONCLUSIONS: The spiral cine DENSE acquisition that has been used at 1.5T to measure cardiac displacements can be applied at 3T with equivalent accuracy. The inter-observer variability and agreement of DENSE-derived peak strains and torsion with HARP is also comparable at both field strengths. Future studies with spiral cine DENSE may take advantage of the additional SNR at 3T

Synchronous Optical and Radio Polarization Variability in the Blazar OJ287

We explore the variability and cross-frequency correlation of the flux density and polarization of the blazar OJ287, using imaging at 43 GHz with the Very Long Baseline Array, as well as optical and near-infrared polarimetry. The polarization and flux density in both the optical waveband and the 43 GHz compact core increased by a small amount in late 2005, and increased significantly along with the near-IR polarization and flux density over the course of 10 days in early 2006. Furthermore, the values of the electric vector position angle (EVPA) at the three wavebands are similar. At 43 GHz, the EVPA of the blazar core is perpendicular to the flow of the jet, while the EVPAs of emerging superluminal knots are aligned parallel to the jet axis. The core polarization is that expected if shear aligns the magnetic field at the boundary between flows of disparate velocities within the jet. Using variations in flux density, percentage polarization, and EVPA, we model the inner jet as a spine-sheath system. The model jet contains a turbulent spine of half-width 1.2 degrees and maximum Lorentz factor of 16.5, a turbulent sheath with Lorentz factor of 5, and a boundary region of sheared field between the spine and sheath. Transverse shocks propagating along the fast, turbulent spine can explain the superluminal knots. The observed flux density and polarization variations are then compatible with changes in the direction of the inner jet caused by a temporary change in the position of the core if the spine contains wiggles owing to an instability. In addition, we can explain a stable offset of optical and near-IR percentage polarization by a steepening of spectral index with frequency, as supported by the data.Comment: 34 pages, 12 figures; To be published in Astrophysical Journal, accepted 03/200