Integer-valued APARCH processes in the analysis of time series of counts

The Asymmetric Power Arch representation for the volatility was introduced by Ding et al.(1993) in order to account for asymmetric responses in the volatility in the analysis of continuous-valued financial time series like, for instance, the log-return series of foreign exchange rates, stock indices or share prices. As reported by Brannas and Quoreshi (2010), asymmetric responses in volatility are also observed in time series of counts such as the number of intra-day transactions in stocks. In this work, an asymmetric power autoregressive conditional Poisson model is introduced for the analysis of time series of counts exhibiting asymmetric overdispersion. Basic probabilistic and statistical properties are summarized and parameter estimation is discussed. A simulation study is presented to illustrate the proposed model. Finally, an empirical application to a set of data concerning the daily number of stock transactions is also presented to attest for its practical applicability in data analysis.

Book review. Cartographies of Time: a history of the timeline.

A review of 'Cartographies of Time: a history of the timeline' by Daniel Rosenberg and Anthony Grafton. Princeton, NJ: Princeton Architectural Press, 2010. (272pp. ISBN: 9781568987637). Keywords: timeline, chronographics

Time in Perspective: a visual approach to models of time

Geographical representations of topographical space come in many shapes and are a regular topic of discussion. The depiction of the invisible and maybe even illusory concept of time on the other hand, remains largely unchanged and undisputed. A uniform and arithmetic model of time fits well with the rigid structure of digital data, which might be why it has been widely adopted within HCI. In our proposal, we will present historic and contemporary approaches that offer alternative perspectives on the visual representation of time. Keywords: timeline, chronographics

Are older people prescribed antidepressants on the basis of fewer symptoms of depression, and for longer periods of time? A survey of 1825 New Zealanders

Aims: To determine whether older people are prescribed antidepressants at lower levels of depression and with fewer symptoms, and whether they are more likely to engage in chronic usage. Methods: An online survey about experiences with, and opinions about, depression and antidepressants, was completed by 1,825 New Zealand adults who had been prescribed antidepressants in the preceding five years. Results: Participants over 55 were prescribed antidepressants with significantly fewer symptoms and were significantly less likely to meet DSM criteria for depression. They were also significantly more likely to have used the drugs for three years and still be using them. Conclusions: Prescribing physicians and their older patients might benefit from discussing the pros and cons of antidepressants (including the additional risk factors with this age group) and the alternatives; and, if prescription does occur, careful monitoring to avoid unnecessary, potentially damaging, long-term use is recommended.

On the assessment of time-shift variations from backscattered ultrasound for large temperature changes in biological phantoms

This work reports the assessment of time-shifts (TS) from backscattered ultrasound (BSU) signals when large temperature variations (up to 15 degrees C) were induced in a gel-based phantom. The results showed that during cooling temperature is linear with TS at a rate of approximately 74 ns/degrees C. However during a complete heating/cooling cycle, the relation is highly non-linear. This can be explained by the fact that during cooling the temperature distribution is more uniform. Another problem to report is that TS is very sensitive to external movements.

Beyond Robotic Wastelands of Time: Abandoned Pedagogical Agents and New Pedalled Pedagogies

Chatbots, known as pedagogical agents in educational settings, have a long history of use, beginning with Alan Turing’s work. Since then online chatbots have become embedded into the fabric of technology. Yet understandings of these technologies are inchoate and often untheorised. Integration of chatbots into educational settings over the past five years suggests an increase in interest in the ways in which chatbots might be adopted and adapted for teaching and learning. This article draws on historical literature and theories that to date have largely been ignored in order to (re)contextualise two studies that used responsive evaluation to examine the use of pedagogical agents in education. Findings suggest that emotional interactions with pedagogical agents are intrinsic to a user’s sense of trust, and that truthfulness, personalisation and emotional engagement are vital when using pedagogical agents to enhance online learning. Such findings need to be considered in the light of ways in which notions of learning are being redefined in the academy and the extent to which new literacies and new technologies are being pedalled as pedagogies in ways that undermine what higher education is, is for, and what learning means.

E-learners’ experiences of time

This paper explores the experiences of e-learners participating in continuing professional development programmes in three UK universities. Data was collected using questionnaires, discussion group postings and informal telephone interviews. These were analysed using two approaches to content analysis: a coding scheme and metaphors. Findings indicated that: e-learners reconstruct their approaches to time management at an early stage in their programme; the e-learners developed different time management strategies (planned, opportunistic, planned/opportunistic); and metaphors illustrated their underlying experiences of time. These provide the basis of recommendations for e-tutors. Finally, the paper explores methodological issues and outlines some implications for practice.

Reduction of trimethylamine N-oxide to trimethylamine by the human gut microbiota: supporting evidence for ‘metabolic retroversion’

Dietary sources of methylamines such as choline, trimethylamine (TMA), trimethylamine N-oxide (TMAO), phosphatidylcholine (PC) and carnitine are present in a number of foodstuffs, including meat, fish, nuts and eggs. It is recognized that the gut microbiota is able to convert choline to TMA in a fermentation-like process. Similarly, PC and carnitine are converted to TMA by the gut microbiota. It has been suggested that TMAO is subject to ‘metabolic retroversion’ in the gut (i.e. it is reduced to TMA by the gut microbiota, with this TMA being oxidized to produce TMAO in the liver). Sixty-six strains of human faecal and caecal bacteria were screened on solid and liquid media for their ability to utilize trimethylamine N-oxide (TMAO), with metabolites in spent media profiled by Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. Enterobacteriaceae produced mostly TMA from TMAO, with caecal/small intestinal isolates of Escherichia coli producing more TMA than their faecal counterparts. Lactic acid bacteria (enterococci, streptococci, bifidobacteria) produced increased amounts of lactate when grown in the presence of TMAO, but did not produce large amounts of TMA from TMAO. The presence of TMAO in media increased the growth rate of Enterobacteriaceae; while it did not affect the growth rate of lactic acid bacteria, TMAO increased the biomass of these bacteria. The positive influence of TMAO on Enterobacteriaceae was confirmed in anaerobic, stirred, pH-controlled batch culture fermentation systems inoculated with human faeces, where this was the only bacterial population whose growth was significantly stimulated by the presence of TMAO in the medium. We hypothesize that dietary TMAO is used as an alternative electron acceptor by the gut microbiota in the small intestine/proximal colon, and contributes to microbial population dynamics upon its utilization and retroversion to TMA, prior to absorption and secondary conversion to TMAO by hepatic flavin-containing monooxygenases. Our findings support the idea that oral TMAO supplementation is a physiologically-stable microbiota-mediated strategy to deliver TMA at the gut barrier.

A matter of time: Phases of customer co-creation community participation and their impact on customer behavior

Despite the growing relevance of co-creating customer communities only little scientific evidence is available on their impact on transactional behavior of participants. Previous research has mostly used self-reported data or distinguished only between during and pre-community phases obtaining mixed results. However, the author proposes that co-creating community activity takes place in five distinguishable phases and changes in transactional behavior are limited to certain phases. Using 33 months of transactional data of a Dutch online auction provider a study was conducted covering all five phases of the community co-creation process from community planning over community set-up, co-development and co-testing to post-launch. The overall results indicate mixed effects of community participation on the different transactional variables during the co-creation process. Community participation had positive effects on auctions listing behavior at the community set-up, co-development and post-launch phases, whereby the number of auctions listed peaked during the community set-up phase. These results suggest that the impact on transactional behavior differs between co-creation phases and different psychological mechanism limited to certain phases might trigger the respective changes.

Towards high-quality simultaneous EEG-fMRI at 7T: Detection and reduction of EEG artifacts due to head motion.

The enhanced functional sensitivity offered by ultra-high field imaging may significantly benefit simultaneous EEG-fMRI studies, but the concurrent increases in artifact contamination can strongly compromise EEG data quality. In the present study, we focus on EEG artifacts created by head motion in the static B0 field. A novel approach for motion artifact detection is proposed, based on a simple modification of a commercial EEG cap, in which four electrodes are non-permanently adapted to record only magnetic induction effects. Simultaneous EEG-fMRI data were acquired with this setup, at 7T, from healthy volunteers undergoing a reversing-checkerboard visual stimulation paradigm. Data analysis assisted by the motion sensors revealed that, after gradient artifact correction, EEG signal variance was largely dominated by pulse artifacts (81-93%), but contributions from spontaneous motion (4-13%) were still comparable to or even larger than those of actual neuronal activity (3-9%). Multiple approaches were tested to determine the most effective procedure for denoising EEG data incorporating motion sensor information. Optimal results were obtained by applying an initial pulse artifact correction step (AAS-based), followed by motion artifact correction (based on the motion sensors) and ICA denoising. On average, motion artifact correction (after AAS) yielded a 61% reduction in signal power and a 62% increase in VEP trial-by-trial consistency. Combined with ICA, these improvements rose to a 74% power reduction and an 86% increase in trial consistency. Overall, the improvements achieved were well appreciable at single-subject and single-trial levels, and set an encouraging quality mark for simultaneous EEG-fMRI at ultra-high field.

Note showing the return of time for the preliminary survey of the Port Robinson and Thorold macadamized road for March and April, 1855

Note showing the return of time for the preliminary survey of the Port Robinson and Thorold macadamized road for March and April, 1855.

Estimate of work done on marsh lands drainage by A. Cook and A. Mains and an estimate of time on the marsh lands survey from September to November

Estimate of work done on marsh lands drainage by A. Cook and A. Mains and an estimate of time on the marsh lands survey from September to November by Fred Holmes, Thomas Baird and Joseph Simpson. This is signed by S.D. Woodruff, Nov. 29, 1855.

How Important Are Intergenerational Transfers of Time? a Macroeconomic Analysis.

This paper examines the implications of intergenerational transfers of time and money for labor supply and capital accumulation. Although intergenerational transfers of time in the form of grandparenting are as substantial as monetary transfers in the data, little is known about the role and importance of time transfers. In this paper, we calibrate an overlapping generations model extended to allow for both time and monetary transfers to the US economy. We use simulations to show that time transfers have important positive effects on capital accumulation and that these effects can be as significant as those of monetary transfers. However, while time transfers increase the labor supply of the young, monetary transfers produce an income effect that tends to decrease work effort. We also find that child care tax credits have little impact on parental time and money transfers, but that a universal child tax credit would increase the welfare of the rich while the poor would benefit from a means-tested program.

Altruism, Intergenerational Transfers of Time and Bequests

This paper uses a standard two-period overlapping generation model to examine the behavior of an economy where both intergenerational transfers of time and bequests are available. While bequests have been examined extensively, time transfers have received little or no attention in the literature. Assuming a log-linear utility function and a Cobb-Douglas production function, we derive an explicit solution for the dynamics and show that altruistic intergenerational time transfers can take place in presence of a binding non-negativity constraint on bequests. We also show that with either type of transfers capital is an increasing function of the intergenerational degree of altruism. However, while with time transfers the labor supply of the young increases with the degree of altruism, with bequests it may decrease