Nature of grand minima and maxima from fully non-linear Flux-Transport Dynamos

We aim to investigate the nature and occurrence characteristics of grand solar minimum and maximum periods, which are observed in the solar proxy records such as 10Be and 14C, using a fully non-linear Babcock-Leighton type flux-transport dynamo including momentum and entropy equations. The differential rotation and meridional circulation are generated from the effect of turbulent Reynolds stress and are subjected to back-reaction from the magnetic field. To generate grand minimum and maximum-like periods in our simulations, we used random fluctuations in the angular momentum transport process, namely the Lambda-mechanism, and in the Babcock-Leighton mechanism. To characterise the nature and occurrences of the identified grand minima and maxima in our simulations, we used the waiting time distribution analyses, which reflects whether the underlying distribution arises from a random or a memory-bearing process. The results show that, in majority of the cases, the distributions of grand minima and maxima reveal that the nature of these events originates from memoryless processes. We also found that in our simulations the meridional circulation speed tends to be smaller during grand maximum, while it is faster during grand minimum periods. The radial differential rotation tend to be larger during grand maxima, while it is smaller during grand minima. The latitudinal differential rotation on the other hand is found to be larger during grand minima.Comment: accepted for publication in Astrophysical Journa

Nonlinear dynamo models using quasi-biennial oscillations constrained by sunspot area data

Contex: Solar magnetic activity exhibits variations with periods between 1.5--4 years, the so-called quasi-biennial oscillations (QBOs), in addition to the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the responsible mechanism for generation of the QBOs. Aims: In this work, we analyse sunspot areas to investigate the spatial and temporal behaviour of the QBO signal and study the responsible physical mechanisms using simulations from fully nonlinear mean-field flux-transport dynamos. Methods: We investigated the behaviour of the QBOs in the sunspot area data in full disk, and northern and southern hemispheres, using wavelet and Fourier analyses. We also ran solar dynamos with two different approaches to generating a poloidal field from an existing toroidal field, Babcock-Leighton and turbulent $\alpha$ mechanisms. We then studied the simulated magnetic field strengths as well as meridional circulation and differential rotation rates using the same methods. Results: The results from the sunspot areas show that the QBOs are present in the full disk and hemispheric sunspot areas and they show slightly different spatial and temporal behaviours, indicating a slightly decoupled solar hemispheres. The QBO signal is generally intermittent and in-phase with the sunspot area data, surfacing when the solar activity is in maximum. The results from the BL-dynamos showed that they are neither capable of generating the slightly decoupled behaviour of solar hemispheres nor can they generate QBO-like signals. The turbulent $\alpha$-dynamos, on the other hand, generated decoupled hemispheres and some QBO-like shorter cycles. Conclusions: In conclusion, our simulations show that the turbulent $\alpha$-dynamos with the Lorentz force seems more efficient in generating the observed temporal and spatial behaviour of the QBO signal compared with those from the BL-dynamos

Economics of collective refusals to supply

This paper examines situations where vertically integrated firms refuse to supply an input to an independent competitor in the downstream market. The treatment of such cases by competition or regulatory authorities is based on the assumption that such outcomes can only arise if there is collusion in the upstream markets. We argue that this is not always the case. In particular, we argue that proper antitrust or regulatory assessment of such cases requires analysis of the nature of competition, the shape and elasticity of the demand curve, the observability of upstream contracts, and even the number of potential downstream competitors

The lost sunspot cycle: New support from Be10 measurements

It has been suggested that the deficit in the number of spots on the surface of the Sun between 1790 and 1830, known as the Dalton minimum, contained an extra cycle that was not identified in the original sunspot record by Wolf. Though this cycle would be shorter and weaker than the average solar cycle, it would shift the magnetic parity of the solar magnetic field of the earlier cycles. This extra cycle is sometimes referred to as the 'lost solar cycle' or 'cycle 4b'. Here we reanalyse Be10 measurements with annual resolution from the NGRIP ice core in Greenland in order to investigate if the hypothesis regarding a lost sunspot cycle is supported by these measurements. Specifically, we make use of the fact that the Galactic cosmic rays, responsible for forming Be10 in the Earth's atmosphere, are affected differently by the open solar magnetic field during even and odd solar cycles. This fact enables us to evaluate if the numbering of cycles earlier than cycle 5 is correct. For the evaluation, we use Bayesian analysis, which reveals that the lost sunspot cycle hypothesis is likely to be correct. We also discuss if this cycle 4b is a real cycle, or a phase catastrophe, and what implications this has for our understanding of stellar activity cycles in general.Comment: accepted for publication in A&

Preventing Rater Biases in 360-Degree Feedback by Forcing Choice

We examined the effects of response biases on 360-degree feedback using a large sample (N=4,675) of organizational appraisal data. Sixteen competencies were assessed by peers, bosses and subordinates of 922 managers, as well as self-assessed, using the Inventory of Management Competencies (IMC) administered in two formats – Likert scale and multidimensional forced choice. Likert ratings were subject to strong response biases, making even theoretically unrelated competencies correlate highly. Modeling a latent common method factor, which represented non-uniform distortions similar to those of “ideal-employee” factor in both self- and other assessments, improved validity of competency scores as evidenced by meaningful second-order factor structures, better inter-rater agreement, and better convergent correlations with an external personality measure. Forced-choice rankings modelled with Thurstonian IRT yielded as good construct and convergent validities as the bias-controlled Likert ratings, and slightly better rater agreement. We suggest that the mechanism for these enhancements is finer differentiation between behaviors in comparative judgements, and advocate the operational use of the multidimensional forced-choice response format as an effective bias prevention method

The effectiveness of visual input enhancement on the noticing and L2 development of the Spanish past tense

Textual manipulation is a common pedagogic tool used to emphasize specific features of a second language (L2) text, thereby facilitating noticing and, ideally, second language development. Visual input enhancement has been used to investigate the effects of highlighting specific grammatical structures in a text. The current study uses a quasi-experimental design to determine the extent to which textual manipulation increase (a) learners’ perception of targeted forms and (b) their knowledge of the forms. Input enhancement was used to highlight the Spanish preterit and imperfect verb forms and an eye tracker measured the frequency and duration of participants’ fixation on the targeted items. In addition, pretests and posttests of the Spanish past tense provided information about participants’ knowledge of the targeted forms. Results indicate that learners were aware of the highlighted grammatical forms in the text; however, there was no difference in the amount of attention between the enhanced and unenhanced groups. In addition, both groups improved in their knowledge of the L2 forms; however, again, there was no differential improvement between the two groups

Effect of organoclay on the physical properties of UV-curable coatings

The combination of UV-curing and nanocomposite technology has been studied to produce cost-effective coatings with superior physical and mechanical properties. The clay was modified with dimethyl dihydrogenated-tallow quaternary ammonium salt and made organophilic. The effect of the organoclay(2-10 phr) on curing rate, mechanical, thermal and physical properties of a urethane-acrylate coating has been determined. X-ray diffraction analysis, AFM, SEM and TEM images as well as the tensile properties of different formulations have confirmed the uniform distribution of organoclay in polymer matrix. At 3 phr organoclay addition, the UV-cured film exhibited the best mechanical performance due to the formation of both intercalated and exfoliated morphologies. Curing time was reduced and the initial thermal decomposition temperature shifted 50°C to higher temperature by the incorporation of small amount of organoclay. The nanocomposite coating was also found to be more resistant against scratching compared with clay-free coating