3,482 research outputs found

    Neuroimaging in predementia Alzheimer’s disease

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    Interaction between current imbalance and magnetization in LHC cables

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    The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents ÂżI, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection the authors performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyze

    Consistency between Treatment Effects on Clinical and Brain Atrophy Outcomes in Alzheimer's Disease Trials

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    Background: Longitudinal changes in volumetric MRI outcome measures have been shown to correlate well with longitudinal changes in clinical instruments and have been widely used as biomarker outcomes in clinical trials for Alzheimer’s disease (AD). While instances of discordant findings have been noted in some trials, especially the recent amyloid-removing therapies, the overall relationship between treatment effects on brain atrophy and clinical outcomes, and how it might depend on treatment target or mechanism, clinical instrument or imaging variable is not yet clear. / Objective: To systematically assess the consistency and therapeutic class-dependence of treatment effects on clinical outcomes and on brain atrophy in published reports of clinical trials conducted in mild cognitive impairment (MCI) and/or AD. / Design: Quantitative review of the published literature. The consistency of treatment effects on clinical and brain atrophy outcomes was assessed in terms of statistical agreement with hypothesized equal magnitude effects (e.g., 30% slowing of both) and nominal directional concordance, as a function of therapeutic class. Setting: Interventional randomized clinical trials. / Participants: MCI or AD trial participants. / Intervention: Treatments included were those that involved ingestion or injection of a putatively active substance into the body, encompassing both pharmacological and controlled dietary interventions. / Measurements: Each trial included in the analysis reported at least one of the required clinical outcomes (ADAS-Cog, CDR-SB or MMSE) and at least one of the required imaging outcomes (whole brain, ventricular or hippocampal volume). / Results: Data from 35 trials, comprising 185 pairwise comparisons, were included. Overall, the 95% confidence bounds overlapped with the line of identity for 150/185 (81%) of the imaging-clinical variable pairs. The greatest proportion of outliers was found in trials of anti-amyloid antibodies that have been shown to dramatically reduce the level of PET-detectable amyloid plaques, for which only 13/33 (39%) of observations overlapped the identity line. A Deming regression calculated using all data points yielded a slope of 0.54, whereas if data points from the amyloid remover class were excluded, the Deming regression line had a slope of 0.92. Directional discordance of treatment effects was also most pronounced for the amyloid-removing class, and for comparisons involving ventricular volume. / Conclusion: Our results provide a frame of reference for the interpretation of clinical and brain atrophy results from future clinical trials and highlight the importance of mechanism of action in the interpretation of imaging results

    The influence of surgery on the development of distant tumour recurrence

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    Tumorrecidief na een in opzet curatieve resectie voor gastro-intestinale tumoren is een groot probleem. Er is zowel een klinische overtuiging als bewijs middels in vivo dierproefonderzoek dat er een relatie bestaat tussen chirurgie en het ontstaan van locoregionaal tumorrecidief. In dit onderzoek wordt de invloed van chirurgisch trauma, een operatie, op het ontstaan van metastasen op afstand bestudeerd in een in vivo diermodel en een in vitro humaan model. Het in vivo model toont aan dat chirurgisch trauma in een rat het aantal longnoduli ten gevolge van systemisch geinjecteerde coloncarcinomacellen bevordert. Deze toename wordt niet veroorzaakt door toename van tumorcelgroei, maar meest waarschijnlijk door verhoogde aanhechting aan het microvasculair endotheel in de long. Onze hypothese is dat de inflammatoire reactie, welke ontstaat tijdens een operatie, de adhesie van circulerende tumorcellen aan het microvasculair endotheel bevordert. De ontstekingsreactie activeert polymorfonucleaire leukocyten, monocyten en macrofagen waarbij zuurstofradicalen en pro-inflammatoire cytokinen vrijkomen. In dit proefschrift laten we in een humaan in vitro model zien dat zuurstofradicalen en pro-inflammatoire cytokinen adhesiemoleculen opreguleren op microvasculaire endotheelcellen op een tijds- en dosisafhankelijke wijze waardoor er significant meer colon- en pancreascarcinomacellen kunnen aanhechten. Deze resultaten tonen duidelijk dat de inflammatoire reactie, welke tengevolge van een operatie optreedt, het ontstaan van metastasen kunnen bevorderen. Maatregelen om tumorrecidief te voorkomen of te verminderen kunnen liggen in het minder traumatisch opereren, zoals de laparoscopie in plaats van de laparotomie, of in het systemisch wegvangen van zuurstofradicalen of pro-inflammatoire cytokinen middels anti-oxidanten en anti-lichamen

    A fiber-optic strain measurement and quench localization system for use in superconducting accelerator dipole magnets

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    A novel fiber-optic measurement system for superconducting accelerator magnets is described. The principal component is an extrinsic Fabry-Perot interferometer to determine localized strain and stress in coil windings. The system can be used either as a sensitive relative strain measurement system or as an absolute strain detector. Combined, one can monitor the mechanical behaviour of the magnet system over time during construction, long time storage and operation. The sensing mechanism is described, together with various tests in laboratory environments. The test results of a multichannel test matrix to be incorporated first in the dummy coils and then in the final version of a 13 T Nb/sub 3/Sn accelerator dipole magnet are presented. Finally, the possible use of this system as a quench localization system is proposed

    Adiabatic normal zone development in MgB2 superconductors

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    A-priori knowledge of the normal zone development in MgB/sub 2/ conductors is essential for quench protection of applications. Therefore the normal zone propagation in a monofilament MgB/sub 2//Fe conductor under near-adiabatic conditions at 4.2 K has been measured and simulated. The results show normal zone propagation velocities up to several meters per second. In addition, by including the voltage-current relation into the computational model, the influence of the n-value on the normal zone propagation is determined. The simulations show that lower n-values suppress the normal zone propagation velocity due to lower heat generation in the MgB/sub 2/ filaments

    Boundary-induced coupling currents in a 1.3 m Rutherford-type cable due to a locally applied field change

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    In this paper the existence of so called Boundary-Induced Coupling Currents (BICCs) is experimentally demonstrated in a 1.3 m long Rutherford-type cable. These BICCs are induced by applying a field change locally onto the cable and can be represented by a non-uniform current distribution between the strands of the cable during and after the field sweep. In order to better understand the characteristic time, amplitude and characteristic length of these coupling currents and the parameters by which they are influenced, a special set-up has been built. With this set-up it is possible to scan the field induced by the BICCs along the full length of a Rutherford-type cable. Special attention is paid on the influence of the contact resistance between crossing strands on the characteristics of the BICCs, and results are presented where parts of the cable are soldered, simulating the joints of a coil
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