Naresuan University Journal
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Motor network efficiency and disability in multiple sclerosis.
No full textOBJECTIVE: To develop a composite MRI-based measure of motor network integrity, and determine if it explains disability better than conventional MRI measures in patients with multiple sclerosis (MS). METHODS: Tract density imaging and constrained spherical deconvolution tractography were used to identify motor network connections in 22 controls. Fractional anisotropy (FA), magnetization transfer ratio (MTR), and normalized volume were computed in each tract in 71 people with relapse onset MS. Principal component analysis was used to distill the FA, MTR, and tract volume data into a single metric for each tract, which in turn was used to compute a composite measure of motor network efficiency (composite NE) using graph theory. Associations were investigated between the Expanded Disability Status Scale (EDSS) and the following MRI measures: composite motor NE, NE calculated using FA alone, FA averaged in the combined motor network tracts, brain T2 lesion volume, brain parenchymal fraction, normal-appearing white matter MTR, and cervical cord cross-sectional area. RESULTS: In univariable analysis, composite motor NE explained 58% of the variation in EDSS in the whole MS group, more than twice that of the other MRI measures investigated. In a multivariable regression model, only composite NE and disease duration were independently associated with EDSS. CONCLUSIONS: A composite MRI measure of motor NE was able to predict disability substantially better than conventional non-network-based MRI measures
Estimating dynamic copula dependence using intraday data
No full textWe estimate the dynamic daily dependence between assets by applying the SCOMDY model (Chen and Fan (2006)) on intraday data. Using tick data of three stock returns the period before and during the credit crisis, we find that our dependence estimator better captures the steep increase in dependence during the onset of the crisis as compared to other commonly used time-varying copula methods. Like other high-frequency estimators, we find that the dependence estimator exhibits long memory and forecast it using a HAR model. We show that for out-of-sample forecasts, our dependence estimator performs better than the constant estimator and other commonly used time-varying copula dependence estimators
Unravelling the origin of large-scale magnetic fields in galaxy clusters and beyond through Faraday Rotation Measures with the SKA
No full textWe investigate the possibility for the SKA to detect and study the magnetic fields in galaxy clusters and in the less dense environments surrounding them using Faraday Rotation Measures. To this end, we produce 3-dimensional magnetic field models for galaxy clusters of different masses and in different stages of their evolution, and derive mock rotation measure observations of background radiogalaxies. According to our results, already in phase I, we will be able to infer the magnetic field properties in galaxy clusters as a function of the cluster mass, down to solar-masses. Moreover, using cosmological simulations to model the gas density, we have computed the expected rotation measure through shock-fronts that occur in the intra-cluster medium during cluster mergers. The enhancement in the rotation measure due to the density jump will permit to constraint the magnetic field strength and structure after the shock passage. SKA observations of polarised sources located behind galaxy clusters will answer several questions about the magnetic field strength and structure in galaxy clusters, and its evolution with cosmic time
Multilevel Modelling in practice: measuring value added for school accountability in Chile
No full textIn the last few decades, school value-added studies have largely demonstrated the effects of socio-economic and demographic characteristics of the schools and the pupils on academic performance. Traditionally, contextualised value-added (CVA) models have been employed in educational research to assess variation in learning outcomes (usually standardised tests of Mathematics and Language) arising from schools and pupils, by implementing multilevel statistical models (2-level models). These models can also be used (and have been used) for informing school accountability to various stakeholders, including policy-makers, head teachers, parents and carers, etc.Despite an overwhelming amount of evidence in favour of the use of such models, government practice in Chile has been restricted to the use of raw school averages in standardised tests (SIMCE tests) as indicators of effectiveness. Nevertheless, a new accountability system that takes into account some of the principles of value-added research is being developed and is soon to be piloted in 2015 by the newly created Chilean Agency for the Quality of Education. The main issue with this new system is that it has been set out to implement multiple linear regression (MLR) models to adjust school averages, which is undoubtedly a major setback. This issue is critical given the high stakes; schools performing insufficiently, as judged by this system, could face closure.Using data from the Chilean National Pupil Database (SIMCE 2004-2006), this study demonstrates that the traditional value-added models (2-level CVA models), let alone MLR models, fall short in addressing the complex phenomenon of academic performance, especially in the context of a developing country. This is because they rather unrealistically assume, amongst other aspects, that a) only the last school attended affects pupils' performance; b) there are no differences between classes within schools; c) school effectiveness does not vary across areas; and d) there are no relationships between different subjects. Ignoring these untenable assumptions results in a large overestimation of the school effects. The novelty of the CVA models in this study is that they extend and improve the traditional 2-level school value-added models insofar as they explicitly assess the variation between pupils, classrooms, primary schools, secondary schools and local authorities, as well as the correlation between Mathematics and Language at all levels.After fitting the extended and more complex CVA models, school accountability measures are derived from them and compared to measures derived from simpler models. A number of key differences are found, leading to the conclusion that further adjustments to the traditional CVA models are not negligible, especially in a highly unequal country such as Chile. The choice of methods for school accountability is therefore a key player in this high stakes game and should not be taken as a trivial matter. A fair policy of school accountability should take a thorough account of the complexity of the school performance phenomenon
ICSID Annulment Procedure and the WTO Appellate System: The Case for an Appellate System for Investment Arbitration
No full textIn comparison to the WTO appellate system, an investment dispute settlement annulment committee has a very limited mandate. Consequently, in recent years, deficiency in the quality of some investment arbitration awards has reinvigorated the debate as to the need for an ICSID appellate facility. While some remain unconvinced of the relevance of such a facility, there is an emerging consensus that the deficiencies in the awards currently being made hinders the predictability of the jurisprudence of investment arbitration and casts doubt on the legitimacy of the system. The ICSID annual report of 2011 recognised the need for an appellate review mechanism for investment arbitration, but subsequent annual reports have been conspicuously silent on this topic and no steps have been taken to follow it up. However, with the WTO disputes settlement system being the only international third party adjudicative body with a functioning appeal system in the area of trade law, it is arguably necessary to think of it as an institution that will inspire the establishment of an investment appeal mechanism. Critics of this potential development argue that the WTO contains a significantly interconnected body of treaty law while the ICSID normally deals with more disparate sets of treaties. Among other things, this contention ignores the existence of customary international law in the crystallisation of both systems. In spite of the debate over the nature of the two systems, there is a need to acknowledge that an appellate system would at least help to improve both the awards and the ICSID’s legitimacy. While recognising the successes as well as the challenges so far faced by the WTO Appellate Body, we argue in this paper that an ICSID appellate system would enhance the legitimacy of investment arbitration, and institute fairness and balance among the various players in investment disputes
Reduced gamma-aminobutyric acid concentration is associated with physical disability in progressive multiple sclerosis.
No full textNeurodegeneration is thought to be the major cause of ongoing, irreversible disability in progressive stages of multiple sclerosis. Gamma-aminobutyric acid is the principle inhibitory neurotransmitter in the brain. The aims of this study were to investigate if gamma-aminobutyric acid levels (i) are abnormal in patients with secondary progressive multiple sclerosis compared with healthy controls; and (ii) correlate with physical and cognitive performance in this patient population. Thirty patients with secondary progressive multiple sclerosis and 17 healthy control subjects underwent single-voxel MEGA-PRESS (MEscher-GArwood Point RESolved Spectroscopy) magnetic resonance spectroscopy at 3 T, to quantify gamma-aminobutyric acid levels in the prefrontal cortex, right hippocampus and left sensorimotor cortex. All subjects were assessed clinically and underwent a cognitive assessment. Multiple linear regression models were used to compare differences in gamma-aminobutyric acid concentrations between patients and controls adjusting for age, gender and tissue fractions within each spectroscopic voxel. Regression was used to examine the relationships between the cognitive function and physical disability scores specific for these regions with gamma-aminobuytric acid levels, adjusting for age, gender, and total N-acetyl-aspartate and glutamine-glutamate complex levels. When compared with controls, patients performed significantly worse on all motor and sensory tests, and were cognitively impaired in processing speed and verbal memory. Patients had significantly lower gamma-aminobutyric acid levels in the hippocampus (adjusted difference = -0.403 mM, 95% confidence intervals -0.792, -0.014, P = 0.043) and sensorimotor cortex (adjusted difference = -0.385 mM, 95% confidence intervals -0.667, -0.104, P = 0.009) compared with controls. In patients, reduced motor function in the right upper and lower limb was associated with lower gamma-aminobutyric acid concentration in the sensorimotor cortex. Specifically for each unit decrease in gamma-aminobutyric acid levels (in mM), there was a predicted -10.86 (95% confidence intervals -16.786 to -4.482) decrease in grip strength (kg force) (P <0.001) and -8.74 (95% confidence intervals -13.943 to -3.015) decrease in muscle strength (P <0.006). This study suggests that reduced gamma-aminobutyric acid levels reflect pathological abnormalities that may play a role in determining physical disability. These abnormalities may include decreases in the pre- and postsynaptic components of gamma-aminobutyric acid neurotransmission and in the density of inhibitory neurons. Additionally, the reduced gamma-aminobutyric acid concentration may contribute to the neurodegenerative process, resulting in increased firing of axons, with consequent increased energy demands, which may lead to neuroaxonal degeneration and loss of the compensatory mechanisms that maintain motor function. This study supports the idea that modulation of gamma-aminobutyric acid neurotransmission may be an important target for neuroprotection in multiple sclerosis.See De Stefano and Giorgio (doi:10.1093/brain/awv213) for a scientific commentary on this article
