Solar Flare Impulsive Phase Emission Observed with SDO/EVE

Differential emission measures (DEMs) during the impulsive phase of solar flares were constructed using observations from the EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed over the temperature range log T = 5.8 - 7.2 allow the evolution of the DEM to be studied over a wide temperature range at 10s cadence. The technique was applied to several M- and X-class flares, where impulsive phase EUV emission is observable in the disk-integrated EVE spectra from emission lines formed up to 3 - 4 MK, and we use spatially-unresolved EVE observations to infer the thermal structure of the emitting region. For the nine events studied the DEMs exhibited a two component distribution during the impulsive phase, a low temperature component with peak temperature of 1 - 2 MK, and a broad high temperature one from 7 - 30 MK. A bimodal high temperature component is also found for several events, with peaks at 8 and 25 MK during the impulsive phase. The origin of the emission was verified using AIA images to be the flare ribbons and footpoints, indicating that the constructed DEMs represent the spatially-average thermal structure of the chromospheric flare emission during the impulsive phase.Comment: 18 pages, 6 figures, accepted for publication in Ap

Factors influencing adoption of conservation tillage in Australian cropping regions

The purpose of this research is to improve understanding of conservation tillage adoption decisions by identifying key biophysical and socio-economic factors influencing no-till adoption by grain growers across four Australian cropping regions. The study is based on interviews with 384 grain growers using a questionnaire aimed at eliciting perceptions relating to a range of possible long- and short-term agronomic interactions associated with the relative economic advantage of shifting to a no-tillage cropping system. Together with other farm and farmer-specific variables, a dichotomous logistic regression analysis was used to identify opportunities for research and extension to facilitate more rapid adoption decisions. The broader systems approach to considering conservation tillage adoption identified important determinants of adoption not associated with soil conservation and erosion prevention benefits. Most growers recognised the erosion-reducing benefits of no-till but it was not an important factor in explaining whether a grower was an adopter or non-adopter. Perceptions associated with shorter-term crop production benefits under no-till, such as the relative effectiveness of pre-emergent herbicides and the ability to sow crops earlier on less rainfall were influential. Employment of a consultant and increased attendance of cropping extension activities were strongly associated with no-till adoption, confirming the information and learning-intensive nature of adopting no-till cropping systems.adoption, conservation tillage, herbicide resistance, no-till, perceptions, weed management, Farm Management,

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

We investigated the response of the solar atmosphere to non-thermal electron beam heating using the radiative transfer and hydrodynamics modelling code RADYN. The temporal evolution of the parameters that describe the non-thermal electron energy distribution were derived from hard X-ray observations of a particular flare, and we compared the modelled and observed parameters. The evolution of the non-thermal electron beam parameters during the X1.5 solar flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for 110 seconds, after which the electron beam heating was ended, and was then allowed to continue evolving for a further 300s. The modelled flare parameters were compared to the observed parameters determined from extreme-ultraviolet spectroscopy. The model produced a hotter and denser flare loop than that observed and also cooled more rapidly, suggesting that additional energy input in the decay phase of the flare is required. In the explosive evaporation phase a region of high-density cool material propagated upward through the corona. This material underwent a rapid increase in temperature as it was unable to radiate away all of the energy deposited across it by the non-thermal electron beam and via thermal conduction. A narrow and high-density ($n_{e} \le 10^{15}$ cm$^{-3}$) region at the base of the flare transition region was the source of optical line emission in the model atmosphere. The collision-stopping depth of electrons was calculated throughout the evolution of the flare, and it was found that the compression of the lower atmosphere may permit electrons to penetrate farther into a flaring atmosphere compared to a quiet Sun atmosphere.Comment: 12 pages, 12 figure

“Long COVID,” Bodily Systems as ADAAA Major Life Activities, and the Social Model of Disability

Long COVID claims for disability-related employment discrimination have been met by physical reductionism during determinations of disability. Difficult to diagnose due to an absence of agreed-upon physiologically observed biomarkers, and liable to elude ADA coverage and/or eligibility for reasonable workplace accommodations, long COVID illustrates a misunderstanding of the relationship between disability, bodily function, and disability anti-discrimination law. Although the ADAAA was intended to extend the range of people considered to be disabled for purposes of disability anti-discrimination law, including bodily system function as a major life activity in the amended statute has contributed to problematic physical reductionism in disability determinations as demonstrated in recent federal court decisions. To remedy this discordance, we suggested how social understandings of the body and disability, congruent with the ADAAA, can counter misleading reductionism about ambiguously diagnosed conditions as disabilities, including long COVID

Influence of cavity lifetime on high-finesse microcavity two-photon absorption photodetectors

For optical pulse incidence as compared with continuous-wave incidence, the enhancement of two-photon absorption inside a high-finesse planar microcavity is reduced, the pulse inside the cavity and the cavity spectrum are broadened. The analysis shows that for transform-limited pulse incidence, the true pulsewidth and the cavity frequency resolution can be estimated if the cavity lifetime or the cavity bandwidth has been obtained from the reflection or transmission spectrum of the cavit

IN MEMORIAM Robert Katz (1917–2011)

Dr. Robert (Bob) Katz, emeritus professor of physics at the University of Nebraska, author of the Katz Model, a deceptively simple but profound parametric model of the action of charged particles on physical and biological systems, died peacefully at his home at Lincoln, NE, on March 12, 2011, after a brief illness. Bob, born in New York City in 1917, and his sister Gladys, were of immigrant Russian Jewish descent. Their parents owned a delicatessen in the Bronx, not far from the Yankee Stadium, where, as Bob recalled, Babe Ruth stopped by for hot dogs, a huge man driving a little sports car, and where Bob saw the New York Giants’ Carl Hubbell pitching a 15-inning shutout at the Polo Grounds, and when doubleheaders cost $1

Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field

In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z > 3.5) AGN activity have been identified. The color selection criteria were established by passing spectra of selected quasars and Seyfert galaxies (appropriately redshifted and modified for "Lyman forest" absorption), as well as stars, observed normal and starburst galaxies, and galaxy models for various redshifts through the filters used for the HDF observations. The actual identification of AGN candidates also involved convolving a Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively flat galactic backgrounds and leaving only the point-like components in the centers. Along with positions and colors, estimated redshifts and absolute magnitudes are reported, with the candidates falling toward the faint end of the AGN luminosity function. One candidate has been previously observed spectroscopically, with a measured redshift of 4.02. The number of sources reported here is consistent with a simple extrapolation of the observed quasar luminosity function to magnitude 30 in B_Johnson. Implications for ionization of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated postscript file). Accepted for publication in the Astronomical Journa

Design and fabrication of highly efficient non-linear optical devices for implementing high-speed optical processing

We present the design and fabrication of micro-cavity semiconductor devices for enhanced Two-Photon-Absorption response, and demonstrate the use of these devices for implementing sensitive autocorrelation measurements on pico-second optical pulses

High-sensitivity two-photon absorption microcavity autocorrelator

A GaAs-AlAs microcavity device has been used as a photodetector in an autocorrelator for measuring the temporal pulsewidth of 1.5-/spl mu/m optical pulses. Enhancement of the two-photon absorption photocurrent due to the microcavity structure results in an autocorrelation (average power times peak power) sensitivity of 9.3/spl times/10/sup -4/ (mW)/sup 2/, which represents two orders of magnitude improvement when compared with conventional autocorrelators