128 research outputs found
Abstracting and extracting: causal coherence and the development of the life story
No full textThis study compared episodic memories of emerging adults (age 18-22) and early adolescents (age 13-15) for life story events and other memories, in an attempt to distinguish characteristics of the life story. Participants were also asked to describe the connection between the stories told. Stories were analyzed for three measures of causal coherence: 1) meaning making, 2) narrative complexity, and 3) the use of causal terms; and one measure of thematic coherence. Results show an impact of age in three measures (meaning making, narrative complexity, and thematic coherence) and of story type (life story vs. non-life story) in all measures. Effects of age show that young adults' narratives showed more evidence of self-related abstract thinking and the ability to see multiple dimensions. Effects of story type indicated that turning point narratives and event connections narratives contained more self-related lessons and insights, displayed greater recognition of complexity, and employed more causal terms. Descriptions of peak experiences and low points did not differ significantly from other episodic memories on these measures of coherence. As well, connections between narratives were more abstract and self-related in the older group and in the life story condition. Findings show that two important narrative characteristics, narrative complexity and reference to self-related lessons and insights develop in adolescence, and are more prevalent in turning point narratives.M.S.Includes bibliographical references (p. 24-28)by Azriel Grysma
Maintaining a positive sense of self: distancing effects in autobiographical memory for negative events
No full textNumerous lines of research have identified that individuals are motivated to remember past events in a way that supports a positive sense of self. Memories of negative events challenge a person’s positive sense of self by suggesting that stable, positive traits that a person considers a part of his or her sense of self may not accurately describe that person. Five possible contributors to the degree to which people find an autobiographical memory challenging to the positive sense of self were identified: when the event occurred, the perspective with which the event is remembered, the person’s age, the person’s gender, and how meaningful the memory was. Participants were asked to identify a positive trait that describes them, and then to write a narrative of an event in which they did not act according to the selected trait. Each participant reported one event, either from the past year or from more than two years ago, and either from the first- or third-person perspective. After reporting the memory, participants completed a brief questionnaire, and responded to three ethical dilemmas (two hypothetical, one actual) that were used to measure participants’ tendency to engage in self-enhancement behavior after reporting the memories. Results found significant differences between emerging adults (age 18-29) and older adults (age 30 and above), and between men and women in the older adult group on numerous measures. Additionally, reported meaning and narrative indicators, such as emotion word use and reported harm to others, predicted performance on self-enhancement measures in both age groups. Time and perspective effects were more equivocal, but these two variables influenced responses, especially through interactions with participant variables (time and gender). Results suggest that threats to a positive sense of self can be alleviated by self-enhancement behavior in unrelated domains. Furthermore, results encourage the practice of analyzing memory narrative content to gain a deeper understanding of the impact of recalling significant events. Finally, results support the practice of considering adult development, both regarding changes in the sense of self and regarding influences of gender at different ages as a variable that shapes the content of autobiographical memories.Ph. D.Includes bibliographical referencesby Azriel Grysma
Statistics and control of waves in disordered media
Get PDFFundamental concepts in the quasi-one-dimensional geometry of disordered
wires and random waveguides in which ideas of scaling and the transmission
matrix were first introduced are reviewed. We discuss the use of the
transmission matrix to describe the scaling, fluctuations, delay time, density
of states, and control of waves propagating through and within disordered
systems. Microwave measurements, random matrix theory calculations, and
computer simulations are employed to study the statistics of transmission and
focusing in single samples and the scaling of the probability distribution of
transmission and transmittance in random ensembles. Finally, we explore the
disposition of the energy density of transmission eigenchannels inside random
media.Comment: 28 Pages, 18 Figures (Review
Probing nonorthogonality of eigenfunctions and its impact on transport through open systems
No full textInternational audienc
Selectively exciting quasi-normal modes in open disordered systems
No full textInternational audienceTransmission through disordered samples can be controlled by illuminating a sample with waveforms corresponding to the eigenchannels of the transmission matrix (TM). But can the TM be exploited to selectively excite quasi-normal modes and so control the spatial profile and dwell time inside the medium? We show in microwave and numerical studies that spectra of the TM can be analyzed into modal transmission matrices of rank unity. This makes it possible to enhance the energy within a sample by a factor equal to the number of channels. Limits to modal selectivity arise, however, from correlation in the speckle patterns of neighboring modes. In accord with an effective Hamiltonian model, the degree of modal speckle correlation grows with increasing modal spectral overlap and non-orthogonality of the modes of non-Hermitian systems. This is observed when the coupling of a sample to its surroundings increases, as in the crossover from localized to diffusive waves
FLUCTUATIONS, CORRELATION AND AVERAGE TRANSPORT OF ELECTROMAGNETIC RADIATION IN RANDOM MEDIA
No full textTransmission Zeros with Topological Symmetry in Complex Systems
Get PDFUnderstanding vanishing transmission in Fano resonances in quantum systems and metamaterials and perfect and ultralow transmission in disordered media, has advanced the understanding and applications of wave interactions. Here we use analytic theory and numerical simulations to understand and control the transmission and transmission time in complex systems by deforming a medium and by adjusting the level of gain or loss. Unlike the zeros of the scattering matrix, the position and motion of the zeros of the determinant of the transmission matrix in the complex plane of frequency and field decay rate have robust topological properties. In systems without loss or gain, the transmission zeros appear either singly on the real axis or as conjugate pairs in the complex plane. As the structure is modified, two single zeros and a complex conjugate pair of zeros may interconvert when they meet at a square root singularity in the rate of change of the distance between the transmission zeros in the complex plane with sample deformation. The transmission time is the spectral derivative of the argument of the determinant of the transmission matrix. It is a sum over Lorentzian functions associated with the resonances of the medium, which is the density of states, and with the zeros of the transmission matrix. Transmission vanishes, and the transmission time diverges as zeros are brought near the real axis. Monitoring the transmission and transmission time when two zeros are close may open up new possibilities for ultrasensitive detection
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