Spectroscopic Observations of Fe XVIII in Solar Active Regions

The large uncertainties associated with measuring the amount of high temperature emission in solar active regions represents a significant impediment to making progress on the coronal heating problem. Most current observations at temperatures of 3 MK and above are taken with broad band soft X-ray instruments. Such measurements have proven difficult to interpret unambiguously. Here we present the first spectroscopic observations of the Fe XVIII 974.86 AA emission line in an on-disk active region taken with then SUMER instrument on SOHO. Fe XVIII has a peak formation temperature of 7.1 MK and provides important constraints on the amount of impulsive heating in the corona. Detailed evaluation of the spectra and comparison of the SUMER data with soft X-ray images from the XRT on Hinode confirm that this line is unblended. We also compare the spectroscopic data with observations from the AIA 94 AA channel on SDO. The AIA 94 AA channel also contains Fe XVIII, but is blended with emission formed at lower temperatures. We find that is possible to remove the contaminating blends and form relatively pure Fe XVIII images that are consistent with the spectroscopic observations from SUMER. The observed spectra also contain the Ca XIV 943.63 AA line that, although a factor 2 to 6 weaker than the Fe XVIII 974.86 AA line, allows us to probe the plasma around 3.5 MK. The observed ratio between the two lines indicates (isothermal approximation) that most of the plasma in the brighter Fe XVIII active region loops is at temperatures between 3.5 and 4 MK.Comment: 12 pages, 5 figures. Submitted as letter to Ap

E-nstructions: A Tool for Electronic Instructions in Laboratory Experiments

E-nstructions facilitates the use of electronic instructions in computerized laboratory experiments in social sciences. In this article I provide a set of guidelines for the installation and the use of E-nstructions.Experiments, Experimental software, Instructions

Are Coronal Loops Isothermal or Multithermal? Yes!

Surprisingly few solar coronal loops have been observed simultaneously with TRACE and SOHO/CDS, and even fewer analyses of these loops have been conducted and published. The SOHO Joint Observing Program 146 was designed in part to provide the simultaneous observations required for in-depth temperature analysis of active region loops and determine whether these loops are isothermal or multithermal. The data analyzed in this paper were taken on 2003 January 17 of AR 10250. We used TRACE filter ratios, emission measure loci, and two methods of differential emission measure analysis to examine the temperature structure of three different loops. TRACE and CDS observations agree that Loop 1 is isothermal with Log T $=$ 5.85, both along the line of sight as well as along the length of the loop leg that is visible in the CDS field of view. Loop 2 is hotter than Loop 1. It is multithermal along the line of sight, with significant emission between 6.2 $<$ Log T $<$ 6.4, but the loop apex region is out of the CDS field of view so it is not possible to determine the temperature distribution as a function of loop height. Loop 3 also appears to be multithermal, but a blended loop that is just barely resolved with CDS may be adding cool emission to the Loop 3 intensities and complicating our results. So, are coronal loops isothermal or multithermal? The answer appears to be yes

Investigating the reliability of coronal emission measure distribution diagnostics using 3D radiative MHD simulations

Determining the temperature distribution of coronal plasmas can provide stringent constraints on coronal heating. Current observations with the Extreme ultraviolet Imaging Spectrograph onboard Hinode and the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory provide diagnostics of the emission measure distribution (EMD) of the coronal plasma. Here we test the reliability of temperature diagnostics using 3D radiative MHD simulations. We produce synthetic observables from the models, and apply the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with the "true" distributions from the model we assess the limitations of the diagnostics, as a function of the plasma parameters and of the signal-to-noise of the data. We find that EMDs derived from EIS synthetic data reproduce some general characteristics of the true distributions, but usually show differences from the true EMDs that are much larger than the estimated uncertainties suggest, especially when structures with significantly different density overlap along the line-of-sight. When using AIA synthetic data the derived EMDs reproduce the true EMDs much less accurately, especially for broad EMDs. The differences between the two instruments are due to the: (1) smaller number of constraints provided by AIA data, (2) broad temperature response function of the AIA channels which provide looser constraints to the temperature distribution. Our results suggest that EMDs derived from current observatories may often show significant discrepancies from the true EMDs, rendering their interpretation fraught with uncertainty. These inherent limitations to the method should be carefully considered when using these distributions to constrain coronal heating.Comment: Accepted for publication on The Astrophysical Journal. 25 pages, 29 figures. Paper version with full resolution images and appendixes can be found at: http://folk.uio.no/bdp/papers/3dEMD_ptesta.pd

On the importance of background subtraction in the analysis of coronal loops observed with TRACE

In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably different. We find differences as well in the related derive filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. With the other subtraction the diagnostics are much less clear. The background subtraction is a delicate issue in the analysis of a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction from interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and of the large amount of subtracted emission in TRACE observations.Comment: 9 pages, 9 figure

Hidden Costs of Control: Three Repetitions and an Extension

We report three repetitions of Falk and Kosfeld's (2006) low and medium control treatments with 364 subjects. Each repetition employs a sample drawn from a standard subject pool of students and demographics vary across samples. Our results largely conflict with those of the original study. We mainly observe hidden costs of control of low magnitude that lead to low-trust principal-agent relationships. Our subjects were asked, at the end of the experimental session, to complete a questionnaire in which they had to state their work motivation in hypothetical scenarios. Our questionnaires are identical to the ones administered in Falk and Kosfeld's (2006) questionnaire study. In contrast to the game play data, our questionnaire data are similar to those of the original questionnaire study. In an attempt to solve this puzzle, we report an extension with 228 subjects where performance-contingent earnings are absent i.e. both principals and agents are paid according to a flat participation fee. We observe that hidden costs outweigh benefits of control which shows that control aversion is more prevalent under hypothetical than under real incentives. Still, in the low control treatment, we observe much weaker negative responses to control in our extension than in the original study. This observation, the fact that the original study uses real incentives, and preliminary findings on the relationship between demographics and the degree of control aversion lead us to conclude that Falk and Kosfeld's (2006) experimental regularities originate from the characteristics of their subjects.Control, Demographics, Experimental Economics, Incentives, Intrinsic Motivation

The Effect of a Reduced-Calorie Diet on alpha-2 Adrenergic Receptor Responsiveness in Abdominal Adipose Tissue in Obese Men During Exercise

There is at present an imperfect understanding of the effect of diet on availability of inhibitory receptors in fat cells during exercise among obese men. &#xd;&#xa;&#xd;&#xa;*Objective:* The purpose of this study was to determine whether diet results in downregulation of alpha-2 adrenergic receptor ([alpha]~2-AR~) messenger RNA (mRNA), improving metabolism in exercise in obese men. &#xd;&#xa;&#xd;&#xa;*Design:* One group, pre-test, post-test design.&#xd;&#xa;&#xd;&#xa;*Measurements:* Subcutaneous abdominal adipose tissue was tested for physiologic response, such as changes in catecholamines and other markers of lipolysis measured during periods of exercise, before and after a 12-week diet. Plasma markers of lipolysis/antilipolytic activity (catecholamines [adrenaline and noradrenaline], NEFA, lactate, glucose, hematocrit, or insulin levels) were analyzed at four points in time in order to determine the effect of exercise on [alpha]~2-AR~ and [beta]-AR responsiveness to sympathetic stimulation.&#xd;&#xa;&#xd;&#xa;*Subjects:* Otherwise healthy 18 to 45 year old obese men (defined as a body mass index (BMI) over 33 kg/m^2^).&#xd;&#xa;&#xd;&#xa;*Results:* The 12-week reduced calorie diet did not result in improved metabolism. Instead, upregulation of alpha-2 adrenergic receptor ([alpha]~2-AR~) messenger RNA (mRNA) was observed. On average, [alpha]~2-AR~ mRNA levels (ratio of [alpha]~2-AR~ to cyclophilin) in subjects increased by 0.022-0.023 after the diet. The average differences in of [alpha]~2-AR~ mRNA and [beta]-AR mRNA measured before and after diet were both insignificant (M = 0.015) t(4) = -0.911; _P_ &#x3e; 0.05; (M = 0.0139; t(4) = 0.077; _P_ &#x3e; 0.05). &#xd;&#xa;&#xd;&#xa;*Conclusion:* The observed direction of change in [alpha]~2-AR~ mRNA levels, when viewed together with the stability of [beta]-AR mRNA levels, suggests that upregulation of [alpha]~2-AR~ rather than downregulation occurred. Downregulation would account for decreased lipolytic activity during exercise, future study is needed