Effect of excess iron on oxidative dehydrogenation of 1-butene over a series of zinc ferrite catalysts

The influence of excess Fe3+ in ZnFe2O4 for the catalytic oxidative dehydrogenation of 1-butene to 1, 3-butadiene was investigated to try to clarify inconsistencies in the existing literature. A series of nanoscale zinc ferrite powders were produced with increasing Fe: Zn ratios. The materials were characterized by a range of techniques, which showed the presence of α-Fe2O3 as a distinct phase with an increasing excess of Fe3+ and SEM highlighted the increased presence of surface structures on the ferrites at higher Fe: Zn ratios. Reaction testing showed α-Fe2O3to be virtually inactive for the oxidative dehydrogenation of 1-butene. Results for the ferrite catalysts showed a significant decrease in both conversion and yield with an increasing excess of Fe3+. Therefore an excess of Fe3+ has a negative effect on catalytic activity and selectivity of zinc ferrite for the oxidative dehydrogenation of 1-butene, but acts as a promoter for competing hydrogenation and combustion side reactions

Intra-subject consistency and reliability of response following 2mA transcranial direct current stimulation

Background Transcranial direct current stimulation (tDCS) is a popular non-invasive brain stimulation technique that has been shown to influence cortical excitability. While polarity specific effects have often been reported, this is not always the case, and variability in both the magnitude and direction of the effects have been observed. Objective/ hypothesis We aimed to explore the consistency and reliability of the effects of tDCS by investigating changes in cortical excitability across multiple testing sessions in the same individuals. A within subjects design was used to investigate the effects of anodal and cathodal tDCS applied to the motor cortex. Four experimental sessions were tested for each polarity in addition to two sham sessions. Methods Transcranial Magnetic Stimulation (TMS) was used to measure cortical excitability (TMS recruitment curves). Changes in excitability were measured by comparing baseline measures and those taken immediately following 20minutes of 2mA stimulation or sham stimulation. Results Anodal tDCS significantly increased cortical excitability at a group level, whereas cathodal tDCS failed to have any significant effects. The sham condition also failed to show any significant changes. Analysis of intra-subject responses to anodal stimulation across four sessions suggest that the amount of change in excitability across sessions was only weakly associated, and was found to have poor reliability across sessions (ICC=0.276). The effects of cathodal stimulation show even poorer reliability across sessions (ICC=0.137). In contrast ICC analysis for the two sessions of sham stimulation reflect a moderate level of reliability (ICC=.424). Conclusions Our findings indicate that although 2mA anodal tDCS is effective at increasing cortical excitability at group level, the effects are unreliable across repeated testing sessions within individual participants. Our results suggest that 2mA cathodal tDCS does not significantly alter cortical excitability immediately following stimulation and that there is poor reliability of the effect within the same individual across different testing sessions

Visuomotor learning and unlearning in children and adolescents with tourette syndrome

Tourette syndrome (TS) is a childhood-onset neurological condition characterised by an evolving repertoire of chronic motor tics and one or more phonic tics. Tics, like habits, are inflexible and repetitive behaviours that are acquired over a period of time. It has been proposed that tics arise in TS as a result of increased habit learning: which may bias the child to acquire automatic behaviours (i.e. tics) more readily than is normal and make it harder to unlearn maladaptive habits once they have been acquired. Using a well-established visuomotor adaptation task, we investigated motor learning in a group of children and adolescents with a clinical diagnosis of TS relative to a group of age and gender matched typically developing individuals. In particular, we quantified differences in the strength and quality of motor learning and unlearning in TS, and the consolidation of motor learning over a 24 hour washout period. We demonstrated that there was a marginally significant decrease in learning rate in the individuals with TS relative to age and gender matched typically developing controls. However, this effect was not associated with tic severity and could be entirely accounted for by the severity of co-occurring ADHD symptoms. Thus, once ADHD symptoms had been accounted for, there were no between group differences in learning rate or the degree of learning observed. By contrast, and more importantly, we found that following learning the rate of forgetting (unlearning) was significantly negatively associated with motor tic severity, such that individuals with more severe tics took longer to unlearn previously learnt motor patterns of behavior. This finding is consistent with the proposal that TS is associated with alterations in the striatal habit learning system and with the view that TS may make it harder to unlearn maladaptive motor habits once they have been acquired

Impaired forward model updating in young adults with Tourette syndrome

Current theories of motor control emphasise how the brain may use internal models of the body to ensure accurate planning and control of movements. One such internal model - a forward model - is thought to generate an estimate of the next motor state and/or the sensory consequences of an upcoming movement, thereby allowing movement errors to be monitored. In addition, forward models may provide a means by which to determine a sense of agency, i.e., the (conscious) sense of authorship and control over our actions. Tourette syndrome is a developmental neurological condition characterised by the occurrence of motor and phonic tics. The involuntary (or voluntary) nature of tics has been the subject of considerable debate, and it was recently argued that the presence of tics in Tourette syndrome could result in a blurring of any subjective boundary between voluntary and involuntary movements. In particular, it was proposed that the level of sensorimotor noise that accompanies tics may be particularly high in Tourette syndrome, and this may contribute to less efficient forward models used to determine agency. We investigated whether the internal monitoring of movements is impaired in individuals with Tourette syndrome, relative to a matched group of typically-developing individuals, using a task that involved executing double-step aiming movements using a hand-held robot manipulandum. Participants were required on each trial to execute two movements in turn, each directed to a remembered target location without visual feedback. Importantly, we assumed that to perform accurately on the second (return) movement it would be necessary to update any forward model to take account errors made during the first (outward) movement. Here we demonstrate that while the Tourette syndrome group were equally accurate, and no more variable, than the matched control group in executing aiming movements to the first (outward) target location. They were significantly less accurate, and exhibited greater movement variability, than controls when executing the second (return) movement. Furthermore, we show that for the return movement only, movement accuracy and movement variability were significantly predicted by the Tourette syndrome group’s clinical severity scores. We interpret these findings as consistent with the view that individuals with Tourette syndrome may experience a reduction in the precision of the forward model estimates thought necessary for the accurate planning and control of movements

Premonitory urges are associated with decreased grey matter thickness within the insula and sensorimotor cortex in young people with Tourette syndrome

Tourette syndrome (TS) is a neurological disorder characterized by vocal and motor tics and is associated with cortical–striatal–thalamic–cortical circuit (CSTC) dysfunction and hyperexcitability of cortical limbic and motor regions, which are thought to lead to the occurrence of tics. Importantly, individuals with TS often report that their tics are preceded by ‘premonitory sensory phenomena’ (PSP) that are described as uncomfortable cognitive or bodily sensations that precede the execution of a tic, and are experienced as a strong urge for motor discharge. While the precise role played by PSP in the occurrence of tics is controversial, PSP are nonetheless of considerable theoretical and clinical importance in TS, not least because they form the core component in many of the behavioural therapies that are currently used in the treatment of tic disorders. In this study, we investigated the brain structure correlates of PSP. Specifically, we conducted a whole-brain analysis of cortical (grey matter) thickness in 29 children and young adults with TS and investigated the association between grey matter thickness and PSP. We demonstrate for the first time that PSP are inversely associated with grey matter thickness measurements within the insula and sensori-motor cortex. We also demonstrate that grey matter thickness is significantly reduced in these areas in individuals with TS relative to a closely age- and gender-matched group of typically developing individuals and that PSP ratings are significantly correlated with tic severity

Applying chiral perturbation to twisted mass Lattice QCD

We have explored twisted mass LQCD (tmLQCD) analytically using chiral perturbation theory, including discretization effects up to O(a^2), and working at next-to-leading (NLO) order in the chiral expansion. In particular we have studied the vacuum structure, and calculated the dependence of pion masses and decay constants on the quark mass, twisting angle and lattice spacing. We give explicit examples for quantities that both are and are not automatically improved at maximal twisting.Comment: 3 pages, 1 figure. Talk given at Lattice2004(spectrum), Fermi National Accelerator Laboratory, June 21 - 26, 2004. v2: Minor typos fixed, slight page format adjustment for generating 3 page postscript at the arXiv. v3: Change to meta-data field only. No change to actual pape

Enhanced saccadic control in young people with Tourette syndrome despite slowed pro-saccades

Tourette syndrome (TS) is a neurodevelopmental disorder characterised by motor and vocal tics. Tics are repetitive and uncontrolled behaviours that have been associated with basal ganglia dysfunction. We investigated saccadic eye movements in a group of young people with TS but without co-morbid ADHD. Participants performed two tasks. One required them to perform only pro-saccade responses (pure pro-saccade task). The other involved shifting, unpredictably, between executing pro- and anti-saccades (mixed saccade task). We show that in the mixing saccade task, the TS group make significantly fewer errors than an age-matched control group, while responding equally fast. By contrast, on the pure pro-saccade task the TS group were shown to be significantly slower to initiate and to complete the saccades (longer movement duration and decreased peak velocity) than controls, while movement amplitude and direction accuracy were not different. These findings demonstrate enhanced shifting ability despite slower reflexive responding in TS and are discussed with respect to a disorder-related adaptation for increased cognitive regulation of behaviour

An exploration of the missing data mechanism in an Internet based smoking cessation trial.

BACKGROUND: Missing outcome data are very common in smoking cessation trials. It is often assumed that all such missing data are from participants who have been unsuccessful in giving up smoking ("missing=smoking"). Here we use data from a recent Internet based smoking cessation trial in order to investigate which of a set of a priori chosen baseline variables are predictive of missingness, and the evidence for and against the "missing=smoking" assumption. METHODS: We use a selection model, which models the probability that the outcome is observed given the outcome and other variables. The selection model includes a parameter for which zero indicates that the data are Missing at Random (MAR) and large values indicate "missing=smoking". We examine the evidence for the predictive power of baseline variables in the context of a sensitivity analysis. We use data on the number and type of attempts made to obtain outcome data in order to estimate the association between smoking status and the missing data indicator. RESULTS: We apply our methods to the iQuit smoking cessation trial data. From the sensitivity analysis, we obtain strong evidence that older participants are more likely to provide outcome data. The model for the number and type of attempts to obtain outcome data confirms that age is a good predictor of missing data. There is weak evidence from this model that participants who have successfully given up smoking are more likely to provide outcome data but this evidence does not support the "missing=smoking" assumption. The probability that participants with missing outcome data are not smoking at the end of the trial is estimated to be between 0.14 and 0.19. CONCLUSIONS: Those conducting smoking cessation trials, and wishing to perform an analysis that assumes the data are MAR, should collect and incorporate baseline variables into their models that are thought to be good predictors of missing data in order to make this assumption more plausible. However they should also consider the possibility of Missing Not at Random (MNAR) models that make or allow for less extreme assumptions than "missing=smoking".RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are