Attachment working models as unconscious structures: An experimental test

Internal working models of attachment (IWMs) are presumed to be largely unconscious representations of childhood attachment experiences. Several instruments have been developed to assess IWMs; some of them are based on self-report and others on narrative interview techniques. This study investigated the capacity of a self-report measure, the Inventory of Parent and Peer Attachment (IPPA; Armsden & Greenberg, 1987), and of a narrative interview method, the Adult Attachment Interview (AAI; George, Kaplan, & Main, 1985), to measure unconscious attachment models. We compared scores on the two attachment instruments to response latencies in an attachment priming task. It was shown that attachment organisation assessed by the AAI correlates with priming effects, whereas the IPPA scales were inversely or not related to priming. The results are interpreted as support for the assumption that the AAI assesses, to a certain degree, unconscious working models of attachment

Numerical field simulation for parallel transmission in MRI at 7 tesla

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 41-42).Parallel transmission (pTx) is a promising improvement to coil design that has been demonstrated to mitigate B1* inhomogeneity, manifest as center brightening, for high-field magnetic resonance imaging (MRI). Parallel transmission achieves spatially-tailored pulses through multiple radiofrequency (RF) excitation coils that can be activated independently. In this work, simulations of magnetic fields in numerical phantoms using an FDTD solver are used to estimate the excitation profiles for an 8-channel RF head coil. Each channel is driven individually in the presence of a dielectric load, and the excitation profiles for all channels are combined post-processing into a B1+ profile of the birdcage (BC) mode. The B1 profile is calculated for a dielectric sphere phantom with material properties of white matter at main magnetic field strengths of 3T and 7T to demonstrate center brightening associated with head imaging at high magnetic field strengths. Measurements of a circular ROI centered in the image show more B1+ inhomogeneity at 7T than at 3T. The B1* profile is then simulated for a numerical head phantom with spatially segmented tissue compartments at 7T. Comparison of the simulated and in vivo B1* profiles at 7T shows agreement in the B1 inhomogeneity. The results provide confidence in numerical simulation as a means to estimate magnetic fields for human imaging. This work will allow further numerical simulations to model the propagation of electric fields within the body, ultimately to provide an estimate of heat deposition in tissue, quantified by the specific absorption rate (SAR), which is a limiting factor of the use of high-field MRI in the clinical setting.by Jessica A. Bernier.S.M

Quantum order by disorder in frustrated diamond lattice antiferromagnets

We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the N\'eel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between $(k,k,0)$-spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc$_2$S$_4$, Co$_3$O$_4$ and CoRh$_2$O$_4$, i.e. specific heat data is a strong evidence for $(k,k,0)$-spiral ordering in all of these materials. This prediction can be tested in future neutron scattering experiments on Co$_3$O$_4$ and CoRh$_2$O$_4$, and is consistent with existing neutron scattering data on MnSc$_2$S$_4$. Based on this agreement we infer a monotonically increasing relationship between frustration and the strength of quantum fluctuations.Comment: 4 pages, 2 figures, version published in PR

Design study for LANDSAT-D attitude control system

The gimballed Ku-band antenna system for communication with TDRS was studied. By means of an error analysis it was demonstrated that the antenna cannot be open loop pointed to TDRS by an onboard programmer, but that an autotrack system was required. After some tradeoffs, a two-axis, azimuth-elevation type gimbal configuration was recommended for the antenna. It is shown that gimbal lock only occurs when LANDSAT-D is over water where a temporary loss of the communication link to TDRS is of no consequence. A preliminary gimbal control system design is also presented. A digital computer program was written that computes antenna gimbal angle profiles, assesses percent antenna beam interference with the solar array, and determines whether the spacecraft is over land or water, a lighted earth or a dark earth, and whether the spacecraft is in eclipse