High-gradient operators in perturbed Wess-Zumino-Witten field theories in two dimensions

Many classes of non-linear sigma models (NLSMs) are known to contain composite operators with an arbitrary number 2s of derivatives ("high-gradient operators") which appear to become strongly relevant within RG calculations at one (or fixed higher) loop order, when the number 2s of derivatives becomes large. This occurs at many conventional fixed points of NLSMs which are perturbatively accessible within the usual epsilon-expansion in d=2+\epsilon dimensions. Since such operators are not prohibited from occurring in the action, they appear to threaten the very existence of such fixed points. At the same time, for NLSMs describing metal-insulator transitions of Anderson localization in electronic conductors, the strong RG-relevance of these operators has been previously related to statistical properties of the conductance of samples of large finite size ("conductance fluctuations"). In this paper, we analyze this question, not for perturbative RG treatments of NLSMs, but for 2d Wess-Zumino-Witten (WZW) models at level k, perturbatively in the current-current interaction of the Noether current. WZW models are special ("Principal Chiral") NLSMs on a Lie Group G with a WZW term at level k. In these models the role of high-gradient operators is played by homogeneous polynomials of order 2s in the Noether currents, whose scaling dimensions we analyze. For the Lie Supergroup G=GL(2N|2N) and k=1, this corresponds to time-reversal invariant problems of Anderson localization in the so-called chiral symmetry classes, and the strength of the current-current interaction, a measure of the strength of disorder, is known to be completely marginal (for any k). We find that all high-gradient (polynomial) operators are, to one loop order, irrelevant or relevant depending on the sign of that interaction.Comment: 22 page

Assessment of fatigue in chronic disease: a bibliographic study of fatigue measurement scales

A large number of fatigue scales exist and there is no consensus on which fatigue measuring scales that are most appropriate for use in assessment of fatigue in different diseases. We aimed to describe the use of fatigue scales in studies of disease-related fatigue during the last three decades. We searched databases from 1975 to 2004 for original studies reporting on disease-related fatigue and extracted information on method used to assess fatigue, diseases under study and year of publication. A total of 2285 papers reported measures of fatigue in chronic non-acute diseases of which 80% were published during the last decade. We identified 252 different ways to measure fatigue, of which 150 were use only once. Multi-symptom scales (n = 156) were used in 670 studies, while 71 scales specifically designed to measure fatigue were applied in 416 studies. The majority of these studies used scales with a multidimensional approach to fatigue, and most studies used scales that were disease-specific or only applied to few different diseases. Research in disease-related fatigue has increased exponentially during the last three decades, even if we adjust for the general increase in publishing activity. The number of scales has also increased and the majority of scales were developed for specific diseases. There is need for measure instruments with different sizes and dimensionality, and due to ceiling and floor effects, the same scale may not be useful for patients with different severity of fatigue. However, since fatigue is an unspecific symptom there should not be need for adopting disease specific fatigue scales for each individual disease. There may be differences in characteristics of fatigue between diseases and generic measurement instruments may facilitate documentation of such differences, which may be of clinical importance

Using endogenous saccades to characterize fatigue in multiple sclerosis

Purpose Multiple Sclerosis (MS) is likely to cause dysfunction of neural circuits between brain regions increasing brain working load or a subjective overestimation of such working load leading to fatigue symptoms. The aim of this study was to investigate if saccades can reveal the effect of fatigue in patients with MS. Methods Patients diagnosed with MS (EDSS<=3) and age matched controls were recruited. Eye movements were monitored using an infrared eyetracker. Each participant performed 40 trials in an endogenous generated saccade paradigm (valid and invalid trials). The fatigue severity scale (FSS) was used to assess the severity of fatigue. FSS scores were used to define two subgroups, the MS fatigue group (score above normal range) and the MS non-fatigue. Differences between groups were tested using linear mixed models. Results Thirty-one MS patients and equal number of controls participated in this study. FSS scores were above the normal range in 11 patients. Differences in saccade latency were found according to group (p<0.001) and trial validity (p=0.023). Differences were 16.9 ms, between MS fatigue and MS non-fatigue, 15.5 ms between MS fatigue and control. The mean difference between valid and invalid trials was 7.5 ms. Differences in saccade peak velocity were found according to group (p<0.001), the difference between MS fatigue and control was 22.3°/s and between MS fatigue and non-fatigue was 12.3°/s. Group was a statistically significant predictor for amplitude (p<0.001). FSS scores were correlated with peak velocity (p=0.028) and amplitude (p=0.019). Conclusion Consistent with the initial hypothesis, our study revealed altered saccade latency, peak velocity and amplitude in patients with fatigue symptoms. Eye movement testing can complement the standard inventories when investigating fatigue because they do not share similar limitations. Our findings contribute to the understanding of functional changes induced by MS and might be useful for clinical trials and treatment decisions.We would like to acknowledge that part of this work has been presented at 3rd International Porto Congress of Multiple Sclerosis, February 27–28, 2015, Porto, Portugal and ECEM 2015 | XVIII. European Conference on Eye Movements, August 16–21, 2015, Viena, Austria. We thank the Multiple Sclerosis Association “Todos com a Esclerose Multiple (TEM)” and the Clinical and Academic Centre (CAA-Hospital de Braga) for their support financial support and for providing facilities for data collection, respectively. We also acknowledge: i) Carla Sofia for recruiting all the MS participants and most of the controls, ii) Two anonymous reviewers for their opinion about an early version of this manuscript and iii) Liz Pearce for proofreading the manuscript. Vision Rehabilitation Lab. receives founding from Shamir Portugal and from grant PTDC/DTP-EPI/0412/2012, Fundação para a Ciência e a Tecnologia, co-financiado pelo FEDER através do COMPETE.info:eu-repo/semantics/publishedVersio

Development and Validity of the Rating-of-Fatigue Scale

Objective: The purpose of these experiments was to develop a rating-of-fatigue (ROF) scale capable of tracking the intensity of perceived fatigue in a variety of contexts. Methods: Four experiments were carried out. The first provided the evidential basis for the construction of the ROF scale. The second tested the face validity of the ROF, and the third tested the convergent and divergent validity of the ROF scale during ramped cycling to exhaustion and 30 min of resting recovery. The final experiment tested the convergent validity of the ROF scale with time of day and physical activity (accelerometer counts) across a whole week. Results: Modal selections of descriptions and diagrams at different levels of exertion and recovery were found during Experiment 1 upon which the ROF scale was constructed and finalised. In Experiment 2, a high level of face validity was indicated, in that ROF was reported to represent fatigue rather than exertion. Descriptor and diagrammatic elements of ROF reportedly added to the coherence and ease of use of the scale. In Experiment 3, high convergence between ROF and various physiological measures were found during exercise and recovery (heart rate, blood lactate concentration, oxygen uptake, carbon dioxide production, respiratory exchange ratio and ventilation rate were all P < 0.001). During ramped cycling to exhaustion ROF and RPE did correspond (P < 0.0001) but not during recovery, demonstrating discriminant validity. Experiment 4 found ROF to correspond with waking time during each day (Mon–Sun all P < 0.0001) and with physical activity (accelerometer count) (Mon–Sun all P < 0.001). Conclusions: The ROF scale has good face validity and high levels of convergent validity during ramped cycling to exhaustion, resting recovery and daily living activities. The ROF scale has both theoretical and applied potential in understanding changes in fatigue in a variety of contexts

Differences in the experience of fatigue in patients and healthy controls: patients' descriptions

Contains fulltext : 51764.pdf ( ) (Open Access)BACKGROUND: The primary objective was to develop an adjective checklist, the Fatigue Quality List (FQL), aimed at assessing different perceptions of fatigue. METHODS: 961 participants filled out the FQL (28 adjectives). A component and confirmatory factor analyses were performed and psychometric properties were evaluated. Differences on factor scores between different patients' groups were investigated and pre- and post treatment scores were compared in demonstrating change of perceptions after treatment of fatigue. RESULTS: Four independent factors were found with adequate psychometric properties. Different perceptions were found between the patients' groups. Patients who were recovered after treatment for fatigue showed similar scores on the factors as healthy controls. CONCLUSION: The FQL appears to be a promising tool in measuring different perceptions of fatigue, which can be especially interesting for clinical practice

Fatigue in neuromuscular disorders: focus on Guillain–Barré syndrome and Pompe disease

Fatigue accounts for an important part of the burden experienced by patients with neuromuscular disorders. Substantial high prevalence rates of fatigue are reported in a wide range of neuromuscular disorders, such as Guillain–Barré syndrome and Pompe disease. Fatigue can be subdivided into experienced fatigue and physiological fatigue. Physiological fatigue in turn can be of central or peripheral origin. Peripheral fatigue is an important contributor to fatigue in neuromuscular disorders, but in reaction to neuromuscular disease fatigue of central origin can be an important protective mechanism to restrict further damage. In most cases, severity of fatigue seems to be related with disease severity, possibly with the exception of fatigue occurring in a monophasic disorder like Guillain–Barré syndrome. Treatment of fatigue in neuromuscular disease starts with symptomatic treatment of the underlying disease. When symptoms of fatigue persist, non-pharmacological interventions, such as exercise and cognitive behavioral therapy, can be initiated