115 research outputs found
Arkansas Corn and Grain Sorghum Performance Tests 2009
Corn and grain sorghum performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating recommendations for producers
Arkansas Soybean Performance Tests 2009
Soybean variety and strain performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture Arkansas Crop Variety Improvement Program. The tests provide information to companies developing varieties and/or marketing seed within the state, and aid the Arkansas Cooperative Extension Service in formulating variety recommendations for soybean producers
Striated AKR Emission: A Remote Tracer of Ion Solitary Structures
We describe the statistical properties of narrowband drifting auroral
kilometric radiation ('striated' AKR) based on observations from the Cluster
wideband receiver during 2002-2005. We show that the observed characteristics,
including frequency drift rate and direction, narrow bandwidth, observed
intensity, and beaming angular sizes are all consistent with triggering by
upward traveling ion solitary structures (`ion holes'). We calculate the
expected perturbation of a horseshoe electron distribution function by an ion
hole by integrating the resonance condition for a cyclotron maser instability
(CMI) using the perturbed velocity distribution. We find that the CMI growth
rate can be strongly enhanced as the horseshoe velocity distribution contracts
inside the passing ion hole, resulting in a power gain increase greater than
100 dB. The gain curve is sharply peaked just above the R-mode cut-off
frequency, with an effective bandwidth ~50 Hz, consistent with the observed
bandwidth of striated AKR emission. Ion holes are observed in situ in the
acceleration region moving upward with spatial scales and speeds consistent
with the observed bandwidth and slopes of SAKR bursts. Hence, we suggest that
SAKR bursts are a remote sensor of ion holes and can be used to determine the
frequency of occurrence, locations in the acceleration region, and lifetimes of
these structures.Comment: 10 pages, 10 figures. J .Geophys. Res. (in press
Adaptive Movement Compensation for In Vivo Imaging of Fast Cellular Dynamics within a Moving Tissue
In vivo non-linear optical microscopy has been essential to advance our knowledge of how intact biological systems work. It has been particularly enabling to decipher fast spatiotemporal cellular dynamics in neural networks. The power of the technique stems from its optical sectioning capability that in turn also limits its application to essentially immobile tissue. Only tissue not affected by movement or in which movement can be physically constrained can be imaged fast enough to conduct functional studies at high temporal resolution. Here, we show dynamic two-photon Ca2+ imaging in the spinal cord of a living rat at millisecond time scale, free of motion artifacts using an optical stabilization system. We describe a fast, non-contact adaptive movement compensation approach, applicable to rough and weakly reflective surfaces, allowing real-time functional imaging from intrinsically moving tissue in live animals. The strategy involves enslaving the position of the microscope objective to that of the tissue surface in real-time through optical monitoring and a closed feedback loop. The performance of the system allows for efficient image locking even in conditions of random or irregular movements
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The correlation of ULF waves and auroral intensity before, during and after substorm expansion phase onset
We present case studies of the evolution of magnetic wave amplitudes and auroral intensity through the late growth phase and the expansion phase of the substorm cycle. We present strong evidence that substorm-related auroral enhancements are clearly and demonstrably linked to ULF wave amplitudes observed at the same location. In most cases, we find that the highest correlations are observed when the magnetometer time series is advanced in time, indicating that the ULF wave amplitudes start to grow before measured auroral intensities, though interestingly this is not always the case. Further we discuss the four possible reasons that may be able to explain both the timing and the high correlations between these two phenomena, including: a simple coincidence, an artifact of instrumental effects, the response of the ionosphere to magnetic waves and auroral particle precipitation, and finally that ULF waves and auroral particle precipitation are physically linked. We discount coincidence and instrumental effects since in the studies presented here they are unlikely or in general will contribute negligible effects, and we find that the ionospheric response to waves and precipitation can explain some, but not all of the results contained within this paper. Specifically, ionospheric response to substorm waves and auroral precipitation cannot explain that the result that previous studies have shown, that onset of ULF wave activity and the onset of auroral particle precipitation occur at the same time and in the same location. This leaves the possibility that ULF waves and auroral particles are physically linked
Post hoc immunostaining of GABAergic neuronal subtypes following in vivo two-photon calcium imaging in mouse neocortex
GABAergic neurons in the neocortex are diverse with regard to morphology, physiology, and axonal targeting pattern, indicating functional specializations within the cortical microcircuitry. Little information is available, however, about functional properties of distinct subtypes of GABAergic neurons in the intact brain. Here, we combined in vivo two-photon calcium imaging in supragranular layers of the mouse neocortex with post hoc immunohistochemistry against the three calcium-binding proteins parvalbumin, calretinin, and calbindin in order to assign subtype marker profiles to neuronal activity. Following coronal sectioning of fixed brains, we matched cells in corresponding volumes of image stacks acquired in vivo and in fixed brain slices. In GAD67-GFP mice, more than 95% of the GABAergic cells could be unambiguously matched, even in large volumes comprising more than a thousand interneurons. Triple immunostaining revealed a depth-dependent distribution of interneuron subtypes with increasing abundance of PV-positive neurons with depth. Most importantly, the triple-labeling approach was compatible with previous in vivo calcium imaging following bulk loading of Oregon Green 488 BAPTA-1, which allowed us to classify spontaneous calcium transients recorded in vivo according to the neurochemically defined GABAergic subtypes. Moreover, we demonstrate that post hoc immunostaining can also be applied to wild-type mice expressing the genetically encoded calcium indicator Yellow Cameleon 3.60 in cortical neurons. Our approach is a general and flexible method to distinguish GABAergic subtypes in cell populations previously imaged in the living animal. It should thus facilitate dissecting the functional roles of these subtypes in neural circuitry
Complex life forms may arise from electrical processes
There is still not an appealing and testable model to explain how single-celled organisms, usually following fusion of male and female gametes, proceed to grow and evolve into multi-cellular, complexly differentiated systems, a particular species following virtually an invariant and unique growth pattern. An intrinsic electrical oscillator, resembling the cardiac pacemaker, may explain the process. Highly auto-correlated, it could live independently of ordinary thermodynamic processes which mandate increasing disorder, and could coordinate growth and differentiation of organ anlage
The 2.5 m Telescope of the Sloan Digital Sky Survey
We describe the design, construction, and performance of the Sloan Digital
Sky Survey Telescope located at Apache Point Observatory. The telescope is a
modified two-corrector Ritchey-Chretien design which has a 2.5-m, f/2.25
primary, a 1.08-m secondary, a Gascoigne astigmatism corrector, and one of a
pair of interchangeable highly aspheric correctors near the focal focal plane,
one for imaging and the other for spectroscopy. The final focal ratio is f/5.
The telescope is instrumented by a wide-area, multiband CCD camera and a pair
of fiber-fed double spectrographs. Novel features of the telescope include: (1)
A 3 degree diameter (0.65 m) focal plane that has excellent image quality and
small geometrical distortions over a wide wavelength range (3000 to 10,600
Angstroms) in the imaging mode, and good image quality combined with very small
lateral and longitudinal color errors in the spectroscopic mode. The unusual
requirement of very low distortion is set by the demands of
time-delay-and-integrate (TDI) imaging; (2) Very high precision motion to
support open loop TDI observations; and (3) A unique wind baffle/enclosure
construction to maximize image quality and minimize construction costs. The
telescope had first light in May 1998 and began regular survey operations in
2000.Comment: 87 pages, 27 figures. AJ (in press, April 2006
Two-Photon Imaging of Calcium in Virally Transfected Striate Cortical Neurons of Behaving Monkey
Two-photon scanning microscopy has advanced our understanding of neural signaling in non-mammalian species and mammals. Various developments are needed to perform two-photon scanning microscopy over prolonged periods in non-human primates performing a behavioral task. In striate cortex in two macaque monkeys, cortical neurons were transfected with a genetically encoded fluorescent calcium sensor, memTNXL, using AAV1 as a viral vector. By constructing an extremely rigid and stable apparatus holding both the two-photon scanning microscope and the monkey's head, single neurons were imaged at high magnification for prolonged periods with minimal motion artifacts for up to ten months. Structural images of single neurons were obtained at high magnification. Changes in calcium during visual stimulation were measured as the monkeys performed a fixation task. Overall, functional responses and orientation tuning curves were obtained in 18.8% of the 234 labeled and imaged neurons. This demonstrated that the two-photon scanning microscopy can be successfully obtained in behaving primates
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