Flash-lag chimeras: the role of perceived alignment in the composite face effect

Spatial alignment of different face halves results in a configuration that mars the recognition of the identity of either face half (). What would happen to the recognition performance for face halves that were aligned on the retina but were perceived as misaligned, or were misaligned on the retina but were perceived as aligned? We used the 'flash-lag' effect () to address these questions. We created chimeras consisting of a stationary top half-face initially aligned with a moving bottom half-face. Flash-lag chimeras were better recognized than their stationary counterparts. However when flashed face halves were presented physically ahead of moving halves thereby nulling the flash-lag effect, recognition was impaired. This counters the notion that relative movement between the two face halves per se is sufficient to explain better recognition of flash-lag chimeras. Thus, the perceived spatial alignment of face halves (despite retinal misalignment) impairs recognition, while perceived misalignment (despite retinal alignment) does not

Measurement error in long-term retrospective recall surveys of earnings

Several recent studies in labour and population economics use retrospective surveys to substitute for the high cost and limited availability of longitudinal survey data. Although a single interview can obtain a lifetime history, inaccurate long-term recall could make such retrospective surveys a poor substitute for longitudinal surveys, especially if it induces non-classical error that makes conventional statistical corrections less effective. In this paper, we use the unique Panel Study of Income Dynamics Validation Study to assess the accuracy of long-term recall data. We find underreporting of transitory events. This recall error creates a non-classical measurement error problem. A limited cost-benefit analysis is also conducted, showing how savings from using a cheaper retrospective recall survey might be compared with the cost of applying the less accurate recall data to a specific policy objective such as designing transfers to reduce chronic poverty

MR-based protein imaging of the human brain by means of dualCEST

Chemical exchange saturation transfer (CEST) is an emerging magnetic resonance imaging (MRI) technique enabling indirect detection of low-concentration cellular compounds in living tissue by their magnetization transfer with water. In particular, protein-attributed CEST signals have been shown to provide valuable diagnostic information for various diseases. While conventional CEST approaches suffer from confounding signals from metabolites and macromolecules, the novel dual-frequency irradiation CEST (dualCEST) technique enables increased protein specificity by selectively detecting the intramolecular spin-diffusion. However, application of this technique has so far been limited to spectroscopic investigations of model solutions at ultrahigh magnetic field strengths. In this thesis, dualCEST was translated to a clinical whole-body MR scanner, enabling protein imaging of the human brain. To this end, several methodological developments were implemented and optimized: (i) improved dual-frequency pulses for signal preparation, (ii) a fast and robust volumetric image readout, (iii) a weighted acquisition scheme, and (iv) an adaptive denoising technique. The resulting improvements are not limited to dualCEST but are relevant for the research field of CEST-MRI in general. Extensive measurements of biochemical model solutions and volunteers demonstrated the protein specificity and reproducibility of dualCEST-MRI. The clinical applicability was verified in pilot studies with tumor and Alzheimer’s patients

The Thermal Structure of Gas in Pre-Stellar Cores: A Case Study of Barnard 68

We present a direct comparison of a chemical/physical model to multitransitional observations of C18O and 13CO towards the Barnard 68 pre-stellar core. These observations provide a sensitive test for models of low UV field photodissociation regions and offer the best constraint on the gas temperature of a pre-stellar core. We find that the gas temperature of this object is surprisingly low (~7-8 K), and significantly below the dust temperature, in the outer layers (Av < 5 mag) that are traced by C18O and 13CO emission. As shown previously, the inner layers (Av > 5 mag) exhibit significant freeze-out of CO onto grain surfaces. Because the dust and gas are not fully coupled, depletion of key coolants in the densest layers raises the core (gas) temperature, but only by ~1 K. The gas temperature in layers not traced by C18O and 13CO emission can be probed by NH3 emission, with a previously estimated temperature of ~10-11 K. To reach these temperatures in the inner core requires an order of magnitude reduction in the gas to dust coupling rate. This potentially argues for a lack of small grains in the densest gas, presumably due to grain coagulation.Comment: 33 pages, 11 figures, accepted by Astrophysical Journa

From a better use of instrumentation to new detection methods in NMR and EPR spectroscopy

NMR and EPR spectroscopy are two of the most important techniques to get quantitative, structural or dynamical information on molecular systems. After covering the fundamentals of these magnetic resonance techniques, this thesis explores ways to improve the usage of current spectrometers and to create new instruments altogether using different detection methods with quantum sensing. First, to deal with bandwidth and oscillating magnetic field limitations typically present for 19F nuclei in NMR or unpaired electrons in EPR, improved methods based on frequency-swept pulses are presented. The implementation of the CHORUS sequence in EPR spectroscopy is detailed. New pulse sequences, namely CHORUSCPMG, PROCHORUS and superposed frequency-swept pulses, are presented in the context of solution-state NMR spectroscopy. Then, on-the-fly optimisation is proposed as a tool to automate EPR experiments and even develop new ones. A software package, ESR-POISE, was released to allow EPR users with commercial spectrometers to access such methods. Finally, the construction of a spectrometer which can conduct magnetic resonance at unconventionally small scales thanks to quantum sensors (NV centres) is detailed. After describing design choices for the different elements of the instrument, a focus is made on the static magnetic field with Finite Element Analysis