488 research outputs found
Performance testing of dimensional X-ray computed tomography systems
X-ray Computed Tomography (XCT) has become a common tool for dimensional analysis as it allows for non-destructive internal and external measurements. Manufacturers often specify the accuracy of dedicated metrology XCT systems as a maximum permissible error (MPE) statement determined using workpieces, test lengths and positions that are significantly different between manufacturers. The VDI/VDE 2630-1.3:2011 guideline provides specification and respective test methods to verify performance against these MPE statements and has been applied in this study to evaluate four different commercial XCT systems in a uniform way. For this examination a multi-sphere test object was developed that explicitly complies with these guidelines and maximises the use of the whole measurement volume, which has then been scaled to test both high and low magnifications. The study consisted of two parts: scans according to a protocol to allow for a fair comparison between all the systems and free scans where manufacturers could show the best capabilities of their system. With these particular objects no system complied with its own MPE statement, however sub voxel accuracies were found. The maximum error in terms of voxels ranged between 0.16 voxel to 0.43 voxel for low magnification (voxel size of 100 μm) and 0.49 voxel to 0.82 voxel for high magnification (voxel size of 14 μm) between systems. This indicates the need for greater standardisation and transparency on how accuracy statements are determined, and more directed protocols for testing the performance of a system. In particular due to the extreme range of measurement volumes and voxel sizes/resolutions XCT are capable of, it is demonstrated that it maybe reasonable to consider an MPE dependent on voxel size
Molecular simulations of adsorption isotherms of small alkanes in FER-, TON-, MTW- and DON-type zeolites
Phosphorus Pentasulfide and Thiophosphoryl Bromide: Facile Reagents for the Reduction of Sulfines to Thiones
Resonant tunnelling features in the transport spectroscopy of quantum dots
We present a review of features due to resonant tunnelling in transport
spectroscopy experiments on quantum dots and single donors. The review covers
features attributable to intrinsic properties of the dot as well as extrinsic
effects, with a focus on the most common operating conditions. We describe
several phenomena that can lead to apparently identical signatures in a bias
spectroscopy measurement, with the aim of providing experimental methods to
distinguish between their different physical origins. The correct
classification of the resonant tunnelling features is an essential requirement
to understand the details of the confining potential or predict the performance
of the dot for quantum information processing.Comment: 18 pages, 7 figures. Short review article submitted to
Nanotechnology, special issue on 'Quantum Science and Technology at the
Nanoscale
Strong coupling between single-electron tunneling and nano-mechanical motion
Nanoscale resonators that oscillate at high frequencies are useful in many
measurement applications. We studied a high-quality mechanical resonator made
from a suspended carbon nanotube driven into motion by applying a periodic
radio frequency potential using a nearby antenna. Single-electron charge
fluctuations created periodic modulations of the mechanical resonance
frequency. A quality factor exceeding 10^5 allows the detection of a shift in
resonance frequency caused by the addition of a single-electron charge on the
nanotube. Additional evidence for the strong coupling of mechanical motion and
electron tunneling is provided by an energy transfer to the electrons causing
mechanical damping and unusual nonlinear behavior. We also discovered that a
direct current through the nanotube spontaneously drives the mechanical
resonator, exerting a force that is coherent with the high-frequency resonant
mechanical motion.Comment: Main text 12 pages, 4 Figures, Supplement 13 pages, 6 Figure
Understanding Behavior in Phelan-McDermid Syndrome
BackgroundPhelan-McDermid syndrome (PMS) or 22q13.3 deletion syndrome is a rare genetic disorder characterized by developmental delay, hypotonia and severely delayed speech. Behavioral difficulties are often reported in PMS, although knowledge of behavioral profiles and the interpretation of reported behavior remains limited. Understanding the meaning of behavior requires considering the context as well as other domains of functioning, for example the individual's level of cognitive, social and emotional development. Combining structured direct in-person neurodevelopmental assessments with contextual assessments to enable meaningful interpretations of reported behavior on functional dimensions across multiple units of analysis, as proposed by the RDoc framework, is essential. MethodsIn this article we present a structured multidisciplinary method of assessment through direct in-person neurodevelopmental assessments and assessment of contextual factors. Our study sample includes data of 33 children with an average age of 6.2 years (range 1.1 to 15.7) with PMS, obtained through individual in-person assessments in combination with parent informed questionnaires. We assessed developmental age using the Bayley-III, adaptive behavior was assessed with the Vineland screener, social-emotional development with the ESSEON-R and behavior by using the CBCL. ResultsOur results show a great deal of variability in phenotypic presentation with regard to behavior, symptom expression and symptom severity in individuals with PMS. The data on behavior is interpreted in the context of the individual's level of cognitive, adaptive development and the (genetic) context. Behavioral data showed high levels of withdrawn behavior and attention problems. More than half of the children showed borderline or clinical symptoms related to Autism Spectrum Disorder (ASD). ConclusionsThe interpretation of the meaning of certain behavior in PMS is often based on questionnaires and descriptions without taking the specific context of development into account. Combining questionnaires with direct in-person assessments measuring different domains of functioning should be considered a more accurate method to interpret the meaning of findings in order to understand behavior in rare genetic disorders associated with developmental delay such as PMS. Direct in-person assessment provides valuable and specific information relevant to understanding individual behavior and inform treatment as well as increase knowledge of the neurodevelopmental phenotype in individuals with PMS. More specific application of the proposed frameworks on behavior in PMS is desirable in making useful interpretations
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