Mapping the secondary star in QQ Vulpeculae

We present high- and medium-resolution phase-resolved far-red spectra of the magnetic cataclysmic variable QQ Vul. The spectra show the Na i doublet absorption features near λ 8190 Å from the cool secondary star, and the lines of He ii, O i, Mg ii, C i, N i, Ca ii and Paschen in emission. Using a Doppler imaging technique, we find that the H i, He ii, C i and O i lines have a narrow component originating near the L1 point and a strong component from the stream, while the Mg ii and Ca ii emission arises solely from the illuminated hemisphere of the red dwarf. We carry out an exhaustive analysis of the emission- and absorption-line velocities and fluxes seen in the QQ Vul spectrum. By simultaneously fitting the radial velocity and flux information we are able to produce surface maps of each line on the secondary star using a technique analogous to the one employed by Davey. The Na i and Mg ii maps show an asymmetric distribution akin to that seen in AM Her. Although the observed velocity semi-amplitudes (K2) of the lines can potentially be corrected for the effects of irradiation, we find that time-dependent changes in the degree of heating on the secondary can lead to large discrepancies in the results, significant enough to give inconsistent values from data taken at different epochs. We discuss the limitations of the surface mapping method as a means of correcting the observed K2. Our results also suggest that the emission features from the red dwarf are likely to be formed at quite high levels of the stellar chromosphere, in some cases probably even beyond the L1 point and inside the Roche lobe of the white dwarf, with the different lines possibly forming at different depths. Using the Na i absorption doublet, we find a velocity semi-amplitude for the secondary star of K2=219±6 km s−1 and a projected rotational velocity of vrot sin i=110±15 km s−1. Thus we estimate the mass ratio to be q=0.54±0.14. Based on the results of the best-fitting surface maps on all the lines, and the nature of the phase-dependent variations of the continuum and lines, we infer a binary inclination of i=65°±7°, and obtain a complete set of binary parameters for QQ Vul. We classify the secondary star as M4V from the TiO band ratios

Architecture-Aware Configuration and Scheduling of Matrix Multiplication on Asymmetric Multicore Processors

Asymmetric multicore processors (AMPs) have recently emerged as an appealing technology for severely energy-constrained environments, especially in mobile appliances where heterogeneity in applications is mainstream. In addition, given the growing interest for low-power high performance computing, this type of architectures is also being investigated as a means to improve the throughput-per-Watt of complex scientific applications. In this paper, we design and embed several architecture-aware optimizations into a multi-threaded general matrix multiplication (gemm), a key operation of the BLAS, in order to obtain a high performance implementation for ARM big.LITTLE AMPs. Our solution is based on the reference implementation of gemm in the BLIS library, and integrates a cache-aware configuration as well as asymmetric--static and dynamic scheduling strategies that carefully tune and distribute the operation's micro-kernels among the big and LITTLE cores of the target processor. The experimental results on a Samsung Exynos 5422, a system-on-chip with ARM Cortex-A15 and Cortex-A7 clusters that implements the big.LITTLE model, expose that our cache-aware versions of gemm with asymmetric scheduling attain important gains in performance with respect to its architecture-oblivious counterparts while exploiting all the resources of the AMP to deliver considerable energy efficiency

HST and ground-based eclipse observations of V2051 Ophiuchi: Binary parameters

We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B ~ 16.2 mag. In comparison to the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ~4 and ~5. Flickering activity is mostly suppressed and the lightcurve shows the eclipse of a compact white dwarf at disc centre which contributes ~60 per cent of the total light at 3900--4300 A. We use measurements of contact phases in the eclipse lightcurve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q= 0.19+/-0.03 and an inclination of i= 83+/-2 degrees. The masses of the component stars are M_1 = 0.78+/-0.06 M_dot and M_2 = 0.15+/-0.03 M_dot. Our photometric model predicts K_1 = 83+/-12 km/s and K_2= 435+/-11 km/s. The predicted value of K_1 is in accordance with the velocity amplitude obtained from the emission lines after a correction for asymmetric line emission in the disc is made (Watts et al. 1986). The secondary of V2051 Oph is significantly more massive than the secondaries of the other ultra-short period dwarf novae. V2051 Oph is probably a relatively young system, whose secondary star had not enough time to evolve out of thermal equilibrium.Comment: 16 pages, 7 postscript figures, coded using MNRAS latex style. To appear in Monthly Notices of the Royal Astronomical Society. Revised version with changes in section 4.3. For related papers and files see ftp://fsc01.fsc.ufsc.br/pub/bap and http://www.fsc.ufsc.br/~astr

Understanding how customers engage with social tourism websites

Purpose: This paper aims to analyse the effect of technology acceptance variables on customer attitude and customer engagement behaviours (CEB) with social tourism websites (STWs). Design/methodology/approach: An empirical study was carried out with 346 customers. A model was developed to analyse the relationships between CEB and their determinants. Partial least squares – structural equation modelling was used to test the model. Findings: Customers’ perceptions of enjoyment, ease of use, usefulness and trustworthiness positively influence their attitude towards STWs and their subsequent engagement behaviours [purchases, word of mouth (WOM) and referrals]. Originality/value: This study develops and empirically tests a model that analyses the impact of technology acceptance model variables on CEB, both transactional (customer purchases) and non-transactional (customer WOM, referrals and feedback), in the context of STWs

The importance of corporate brand identity in business management: An application to the UK banking sector

Corporate brand identity management is a key issue for any organisation. Accordingly, its study is a research field of great interest. This paper seeks to broaden the understanding of this strategic activity and its effects. Specifically, it investigates the concept of corporate brand identity from the employees' perspective in the UK financial banking sector and analyses the link between brand identity management and employees' attitudes and behaviours. Results indicate that organisations should pay special attention to the corporate brand identity management, given its influence on employees' commitment with their organisations, as well as their brand performance and satisfaction

Gamification in sport apps: the determinants of users'' motivation

Purpose: Gamification is a tool with great potential to motivate individuals to increase their physical activity. That is why sport apps for mobile devices, such as Nike+ or Strava, have integrated game elements. There is, however, little evidence of gamification''s effectiveness in this field. Therefore, the aim of the present study is to analyze the impact of game elements included in gamified sports'' apps on the satisfaction of basic psychological needs (i.e. competence, autonomy and relatedness). Similarly, the research analyzes the impact of these needs on autonomous motivation. Design/methodology/approach: To achieve these goals, data were collected from users of gamified sport apps, using an online questionnaire. The data were analyzed using partial least squares structural equation modeling. Findings: The results showed that interaction in the app with achievement-related game elements satisfied the needs for competence, autonomy and relatedness; social-related elements satisfied the need for relatedness; and immersion-related elements satisfied the needs for competence and autonomy. Similarly, satisfaction of the needs for autonomy and relatedness while using the app is crucial to experience autonomous motivation. Practical implications: The findings of this study provide guidelines for practitioners and app developers. Originality/value: Based on self-determination theory, the paper provides new insights into the relationship between game elements included in sport apps and individuals'' basic psychological needs and motivation

Flow and business simulation games: A typology of students

In the context of management training business simulation games are increasingly emerging as pedagogical tools for motivating and engaging players actively in the learning experience. Business simulation games provide opportunities for students to enter the flow state. However, few studies have applied flow theory in this specific context. Using data from a two-wave longitudinal study with a sample of 430 students who played a business simulation game, this research draws on the four-channel model of flow to identify subgroups of students based on their levels of skill and challenge and to analyse the evolution of their optimal experience of flow. In addition, it explores whether students in flow achieve higher learning outcomes; in particular, students’ perceived learning, satisfaction and skills development