Magnetic Activity in Thick Accretion Disks and Associated Observable Phenomena: II. Flux Storage

In paper I, we have studied the conditions under which flux tubes are expelled from adiabatic thick accretion disks. In the present paper, we explore a few other models of thick disks, where flux tubes could be stored. We show that flux tubes with sufficiently weak fields are not expelled out if they move adiabatically inside an isothermal disk; they continue to oscillate around mean equipotential surfaces inside the disk. If the field in the flux tube is amplified due to the shear, they are eventually expelled away. We explore a `toy' model also, where the entropy increase outwards from the center of the thick disk and find a similar behavior. Flux storage in the disk, as in the case of the sun, in general, enhances the possibility of sustained magnetic activity formation of coronae in the chimney region. The existence of coronae on the disk surface may explain the short-time variability in the spectra of Blazars and the emission of energetic particles from AGNs and Quasars. It may also supply matter to the cosmic jets through magnetized winds.Comment: LaTeX, 27 pages, Astrophysical Journal (In press), March 20th Issu

Long-Term Measurements of Sunspot Magnetic Tilt Angles

Tilt angles of close to 30,600 sunspots are determined using Mount Wilson daily averaged magnetograms taken from 1974 to 2012, and MDI/SoHO magnetograms taken from 1996 to 2010. Within a cycle, more than 90% of sunspots have a normal polarity alignment along the east-west direction following Hale's law. The median tilts increase with increasing latitude (Joy's law) at a rate of ~0.5 degree per degree of latitude. Tilt angles of spots appear largely invariant with respect to time at a given latitude, but they decrease by ~0.9degree per year on average, a trend which largely reflects Joy's law following the butterfly diagram. We find an asymmetry between the hemispheres in the mean tilt angles. On average, the tilts are greater in the southern than in the northern hemisphere for all latitude zones, and the differences increase with increasing latitude.Comment: 29 pages, 13 figures, to appear on ApJ, October 20, 2012 website: http://www2.ess.ucla.edu/~jingli/ApJ201210

External auditor independence: selected group perceptions

The professional independence of external auditors is fundamental to the auditing profession. Thus, it is important that auditors are not only independent in fact, but that they are also seen to be independent - i. e. independent in aPRearance. In that light, it is clear that external auditor independence (EAI) is a perceptual issue. Yet there is a marked lack of empirical research done with a view to determine how users of audited accounts perceive EAI, or to contrast such views with comparable ones held by external auditors themselves. Thus, the major objective of the research is to empirically examine how relevant groups see EAI within specified audit situations. The research examines how three groups of users of audited statements (bankers, credit managers and internal auditors - the user groups) and sets of external auditors (who issue audit reports - the issuer groups), see EAI in circumstances described in specific audit situations. This is the primary context of the empirical research. An appropriate questionnaire was developed and used as the research instrument because of its natural accord with the Brunswick Lens Model approach to perceptual examinations. The facts specified in each of the twenty situations were cues upon which judgement of EAI, was made by judges (the questionnaire respondents). Thus, the empirical chapters consider: 1. Areas of concern with EAI 2. Significant perceptual differences: a) between each user group and the issuer group b) within two sub-groups of the issuer group 3. Possible explanations for differences by examining: a) the dimensions underlying group views of EAI b) the importance attached by groups to EAI cues c) the pattern between bio-data and views on EAI main findings indicate, within an EAI context: 1. Significant differences of perception between the issuer group and each of the three user groups. 2. Generally non-significant differences of perception within the external auditor group. 3. Each group having its own unique set of underlying (factor or dimensional) constructs. 4. The cues (facts) contained in audit environments are of consequence in explaining such group differences. 5. Personal group characteristics (attributes) do not appear to be very helpful in explaining group views

The physics of twisted magnetic tubes rising in a stratified medium: two dimensional results

The physics of a twisted magnetic flux tube rising in a stratified medium is studied using a numerical MHD code. The problem considered is fully compressible (no Boussinesq approximation), includes ohmic resistivity, and is two dimensional, i.e., there is no variation of the variables in the direction of the tube axis. We study a high plasma beta case with small ratio of radius to external pressure scaleheight. The results obtained can therefore be of relevance to understand the transport of magnetic flux across the solar convection zone.Comment: To be published in ApJ, Vol. 492, Jan 10th, 1998; 25 pages, 16 figures. NEW VERSION: THE PREVIOUS ONE DIDN'T PRINT CORRECTLY. The style file overrulehere.sty is include

Predicting the temporal activity patterns of new venues.

Estimating revenue and business demand of a newly opened venue is paramount as these early stages often involve critical decisions such as first rounds of staffing and resource allocation. Traditionally, this estimation has been performed through coarse-grained measures such as observing numbers in local venues or venues at similar places (e.g., coffee shops around another station in the same city). The advent of crowdsourced data from devices and services carried by individuals on a daily basis has opened up the possibility of performing better predictions of temporal visitation patterns for locations and venues. In this paper, using mobility data from Foursquare, a location-centric platform, we treat venue categories as proxies for urban activities and analyze how they become popular over time. The main contribution of this work is a prediction framework able to use characteristic temporal signatures of places together with k-nearest neighbor metrics capturing similarities among urban regions, to forecast weekly popularity dynamics of a new venue establishment in a city neighborhood. We further show how we are able to forecast the popularity of the new venue after one month following its opening by using locality and temporal similarity as features. For the evaluation of our approach we focus on London. We show that temporally similar areas of the city can be successfully used as inputs of predictions of the visit patterns of new venues, with an improvement of 41% compared to a random selection of wards as a training set for the prediction task. We apply these concepts of temporally similar areas and locality to the real-time predictions related to new venues and show that these features can effectively be used to predict the future trends of a venue. Our findings have the potential to impact the design of location-based technologies and decisions made by new business owners

Predicting the temporal activity patterns of new venues

Estimating revenue and business demand of a newly opened venue is paramount as these early stages often involve critical decisions such as first rounds of staffing and resource allocation. Traditionally, this estimation has been performed through coarse-grained measures such as observing numbers in local venues or venues at similar places (e.g., coffee shops around another station in the same city). The advent of crowdsourced data from devices and services carried by individuals on a daily basis has opened up the possibility of performing better predictions of temporal visitation patterns for locations and venues. In this paper, using mobility data from Foursquare, a location-centric platform, we treat venue categories as proxies for urban activities and analyze how they become popular over time. The main contribution of this work is a prediction framework able to use characteristic temporal signatures of places together with k-nearest neighbor metrics capturing similarities among urban regions, to forecast weekly popularity dynamics of a new venue establishment in a city neighborhood. We further show how we are able to forecast the popularity of the new venue after one month following its opening by using locality and temporal similarity as features. For the evaluation of our approach we focus on London. We show that temporally similar areas of the city can be successfully used as inputs of predictions of the visit patterns of new venues, with an improvement of 41% compared to a random selection of wards as a training set for the prediction task. We apply these concepts of temporally similar areas and locality to the real-time predictions related to new venues and show that these features can effectively be used to predict the future trends of a venue. Our findings have the potential to impact the design of location-based technologies and decisions made by new business owners

Local sales restrictions significantly reduce the availability of menthol tobacco: findings from four Minnesota cities

BACKGROUND In 2017 and 2018, Minneapolis, St. Paul, Duluth and Falcon Heights, Minnesota were among the first US cities to restrict the sale of menthol tobacco to adult-only stores. The study examined changes in the availability and marketing of these products following policy implementation. METHODS Retail store audits were conducted approximately 2 months pre-policy and post-policy implementation. Tobacco retail stores (n=299) were sampled from tobacco licensing lists in Minneapolis, St. Paul, Duluth and Falcon Heights, as well as six comparison cities without menthol policies. The presence of menthol tobacco was assessed, along with the number of interior and exterior tobacco ads and promotions at each store. RESULTS The majority of policy intervention stores (grocery, convenience stores and pharmacies) were compliant (Minneapolis, 84.4%; Duluth, 97.5%; and St. Paul and Falcon Heights, 100.0%) and did not sell menthol tobacco. In contrast, menthol tobacco was available in all comparison city stores, and most (96.0%) exempted tobacco shops and liquor stores post-policy implementation. Two Minneapolis convenience stores added interior tobacco shops, allowing them to continue selling menthol tobacco. Significant decreases in menthol tobacco marketing post-policy were observed in the stores' interior in Minneapolis, St. Paul and Duluth (p<0.001) and on the stores' exterior in Duluth (p=0.023). CONCLUSIONS Findings demonstrate high rates of compliance, indicating that sales restrictions can significantly reduce the availability of menthol tobacco. However, challenges to policy adherence underscore the need for continued monitoring and enforcement action

Turbulent Erosion of Magnetic Flux Tubes

Results from a numerical and analytical investigation of the solution of a nonlinear axially symmetric diffusion equation for the magnetic field are presented for the case when the nonlinear dependence of the diffusivity nu(B) on the magnetic field satisfies basic physical requirements. We find that for sufficiently strong nonlinearity (i.e. for sufficiently strong reduction of nu inside the tube) a current sheet is spontaneously formed around the tube within one diffusion timescale. This sheet propagates inwards with a velocity inversely proportional to the ratio of the field strength just inside the current sheet to the equipartition field strength B0/Be, so the lifetime of a tube with constant internal flux density is increased approximately by a factor not exceeding B0/Be, even for infinitely effective inhibition of turbulence inside the tube. Among the applications of these results we point out that toroidal flux tubes in the solar convective zone are subject to significant flux loss owing to turbulent erosion on a timescale of about 1 month, and that turbulent erosion may be responsible for the formation of a current sheet around a sunspot. It is further proposed that, despite the simplifying assumptions involved, our solutions correctly reflect the essential features of the sunspot decay process.Comment: 17 pages, 11 figure

Pongamia seed cake as a valuable source of plant nutrients for sustainable agriculture

Pongamia, a multipurpose leguminous tree containing non-edible oil, grows widely in India. Oil extracted from the seeds of Pongamia is used as energy source as well as in tanneries while the cake (a byproduct after extracting oil) was found to be rich in all plant nutrients in general and nitrogen (4.28%) and sulfur (0.19%) in particular. Both nitrogen and sulfur were found to be deficient in 100 and 80%, respectively, in soil samples from farmers' fields in Powerguda village of Adilabad district, Andhra Pradesh, India. Use of Pongamia seed cake as a source of plant nutrients for maize, soyabean and cotton was found beneficial in participatory research and development trials on farmers' fields. Further, application of critically deficient micronutrients such as zinc and boron and secondary nutrient sulfur increased crop yields by 16.7 and 19% in soyabean and cotton, respectively. In addition, B:C ratios of 5.03, 1.81 and 2.04 were obtained for soyabean, maize and cotton, respectively, with use of cake as a source of N, however it needed higher initial investment