An error analysis of probabilistic fibre tracking methods: average curves optimization

Fibre tractography using diffusion tensor imaging is a promising method for estimating the pathways of white matter tracts in the human brain. The success of fibre tracking methods ultimately depends upon the accuracy of the fibre tracking algorithms and the quality of the data. Uncertainty and its representation have an important role to play in fibre tractography methods to infer useful information from real world noisy diffusion weighted data. Probabilistic fibre tracking approaches have received considerable interest recently for resolving orientational uncertainties. In this study, an average curves approach was used to investigate the impact of SNR and tensor field geometry on the accuracy of three different types of probabilistic tracking algorithms. The accuracy was assessed using simulated data and a range of tract geometries. The average curves representations were employed to represent the optimal fibre path of probabilistic tracking curves. The results are compared with streamline tracking on both simulated and in vivo data

The relationship between betting and lottery play: a high frequency time-series analysis

The substitutability of different gambling products is an important concern for any jurisdiction contemplating deregulation of its gambling sector. We apply a novel daily time-series data set of daily turnover from one of Britain's leading bookmakers to analyse potential substitution between lottery play and bookmaker betting. We find some evidence that bettors do substitute away from horse race, dog race and numbers betting when the effective price of lottery tickets is unusually low, i.e. when there is a rollover or Superdraw. This substitution has a highly specific pattern of timing that varies by sector. Our results further suggest that bettors rationally engage in forward-looking substitution within their betting portfolios.

Twist operator correlation functions in O(n) loop models

Using conformal field theoretic methods we calculate correlation functions of geometric observables in the loop representation of the O(n) model at the critical point. We focus on correlation functions containing twist operators, combining these with anchored loops, boundaries with SLE processes and with double SLE processes. We focus further upon n=0, representing self-avoiding loops, which corresponds to a logarithmic conformal field theory (LCFT) with c=0. In this limit the twist operator plays the role of a zero weight indicator operator, which we verify by comparison with known examples. Using the additional conditions imposed by the twist operator null-states, we derive a new explicit result for the probabilities that an SLE_{8/3} wind in various ways about two points in the upper half plane, e.g. that the SLE passes to the left of both points. The collection of c=0 logarithmic CFT operators that we use deriving the winding probabilities is novel, highlighting a potential incompatibility caused by the presence of two distinct logarithmic partners to the stress tensor within the theory. We provide evidence that both partners do appear in the theory, one in the bulk and one on the boundary and that the incompatibility is resolved by restrictive bulk-boundary fusion rules.Comment: 18 pages, 8 figure

Giving Patterns By Religious And Non-Religions People

Using the Oaxaca-Blinder (1994) decomposition method to compare the giving levels of money and time of those who claim to attend religious services on a regular basis with those who do not, we find that on average religious people donate more money and time than non-religious people; although a large portion of the average difference is unexplained. We propose that these differences arise from a culture of giving in which religious people are embedded. It may be that individuals who are religious are more likely to be exposed to a culture that encourages giving and volunteering, and will therefore be more likely to give and volunteer

Effects Of Socio-Economic Characteristics On The Medication Of Children For Attention-Deficit/Hyperactivity Disorder (ADHD)

The diagnosis and medication of the illness known as Attention deficit/hyperactivity disorder (ADHD) has been shown to exhibit patterns unexpected from a medical condition that is randomly distributed throughout the population. This research uses new data to show statistically significant relationships between the medication of children for ADHD and several socio-economic characteristics. Most alarming is the fact that the significant relationships between medication and race and gender are robust, even when other socioeconomic characteristics are controlled for

Placing Confidence Limits on Polarization Measurements

The determination of the true source polarization given a set of measurements is complicated by the requirement that the polarization always be positive. This positive bias also hinders construction of upper limits, uncertainties, and confidence regions, especially at low signal-to-noise levels. We generate the likelihood function for linear polarization measurements and use it to create confidence regions and upper limits. This is accomplished by integrating the likelihood function over the true polarization (parameter space), rather than the measured polarization (data space). These regions are valid for both low and high signal-to-noise measurements.Comment: 8 pages, 3 figures, 1 table, submitted to PAS

Giving In A Time Of Terrorism

Recent research in psychology suggest that altruism and altruistic decisions may, in fact, be endogenous and depend on the social situation in which people find themselves. People are more likely to be altruistic, to give to charities and others in need, when they feel secure and safe. This paper looks at the implications of a person’s perceived state of security on giving now that there are terrorist threats in the U.S. We use data from the Center on Philanthropy Panel Study (COPPS), and the Panel Study of Income Dynamics (the PSID) to test for endogenous changes in giving and volunteering from before and after the 2001 terrorist attacks. We find evidence indicating that increasing uncertainty resulted in a decline in the giving of both money and time, holding other variables constant, but the relationship is not significant

First-principles thermoelasticity of bcc iron under pressure

We investigate the elastic and isotropic aggregate properties of ferromagnetic bcc iron as a function of temperature and pressure by computing the Helmholtz free energies for the volume-conserving strained structures using the first-principles linear response linear-muffin-tin-orbital method and the generalized-gradient approximation. We include the electronic excitation contributions to the free energy from the band structures, and phonon contributions from quasi-harmonic lattice dynamics. We make detailed comparisons between our calculated elastic moduli and their temperature and pressure dependences with available experimental and theoretical data.Comment: 5 figures, 2 table