Library as Agent of [Re]Contextualization

Paper presented at the Digital Humanities 2009 conference in College Park, Maryland

Library as Agent of [Re]Contextualization

Paper presented at the Digital Humanities 2009 conference in College Park, Maryland

Evolutionary Subject Tagging in the Humanities; Supporting Discovery and Examination in Digital Cultural Landscapes

In this paper, the authors attempt to identify problematic issues for subject tagging in the humanities, particularly those associated with information objects in digital formats. In the third major section, the authors identify a number of assumptions that lie behind the current practice of subject classification that we think should be challenged. We move then to propose features of classification systems that could increase their effectiveness. These emerged as recurrent themes in many of the conversations with scholars, consultants, and colleagues. Finally, we suggest next steps that we believe will help scholars and librarians develop better subject classification systems to support research in the humanities.NEH Office of Digital Humanities: Digital Humanities Start-Up Grant (HD-51166-10

Evolutionary Subject Tagging in the Humanities

Interdisciplinary research in the humanities requires indexing that represents multiple disciplinary perspectives. Most literature has been indexed using traditional models for subject analysis that are either too broad to be helpful or represent a single disciplinary perspective. We question whether traditional print models of subject analysis serve humanistic researchers' needs in working with digital content. It is beyond the capacity of libraries to re-index this body of literature relying on human indexers. We need to develop scalable tools to both re-index extant bodies of literature and newly created literature. Web-scale searching, computational text analysis, and automated indexing each hold promise for addressing various aspects of the problem, but none seem to fully address the problem. This project will gather a group of scholars with expertise in the humanities, computational analysis of texts, and library and information science, to design an approach to the problem

The influence of a Hamiltonian vibration vs a bath vibration on the 2D electronic spectra of a homodimer

We elucidate the influence of the system–bath boundary placement within an open quantum system, with emphasis on the two-dimensional electronic spectra, through the application of the hierarchical equations of motion formalism for an exciton system. We apply two different models, the Hamiltonian vibration model (HVM) and bath vibration model (BVM), to a monomer and a homodimer. In the HVM, we specifically include the vibronic states in the Hamiltonian capturing vibronic quenching, whereas in the BVM, all vibrational details are contained within the bath and described by an underdamped spectral density. The resultant spectra are analyzed in terms of energetic peak position and thermodynamic broadening precision in order to evaluate the efficacy of the two models. The HVM produces 2D spectra with accurate peak positional information, while the BVM is well suited to modeling dynamic peak broadening. For the monomer, both models produce equivalent spectra in the limit where additional damping associated with the underdamped vibration in the BVM approaches zero. This is supported by analytical results. However, for the homodimer, the BVM spectra are redshifted with respect to the HVM due to an absence of vibronic quenching in the BVM. The computational efficiency of the two models is also discussed in order to inform us of the most appropriate use of each method

Longitudinal fields of quantized Laguerre-Gaussian modes

Longitudinal fields of quantized Laguerre-Gaussian modes are derived, revealing their importance even for light that may be considered to be propagating in the paraxial regime. This is in contrast to unstructured laser light, e.g. a Gaussian beam, where the magnitude of longitudinal components only become important under strong-focusing of the source. The unique effects stem specifically from the optical angular momentum, both orbital and spin, of optical vortex light, and include spin-orbit interactions in freely-propagating circularly-polarized vortices in free-space. The contribution that longitudinal fields make to the rate of single-photon absorption is calculated, highlighting that for optical vortices they cannot be neglected in general

Polariton mediated resonance energy transfer in a fluid

The focus of this work is on a microscopic quantum electrodynamical understanding of cumulative quantum effects in resonance energy transfer occurring in an isotropic and disordered medium. In particular, we consider quantum coherence, defined in terms of interferences between Feynman pathways, and analyze pure-amplitude and phase cross terms that appear in the Fermi golden rule rate equation that results from squaring the matrix element for mediated energy transfer. It is shown that pure-amplitude terms dominate in the near-zone when chromophores are close in proximity to one another (within a few nanometers), and phase cross terms dominate toward the far-zone when phase differences between different Feynman pathways begin to emerge. This can be understood in terms of physical attributes of the mediating photon, whose character becomes more real at long distances, coinciding with vanishing longitudinal components of the field, as transverse components begin to dominate

Excitonic coupling in covalently-bound Perylene Bisimide dimers revealed by two-dimensional electronic spectroscopy

Supramolecular structures based on Perylene Bisimides (PBIs) have been extensively studied because of their fundamental photophysical properties and for their application in a range of different optoelectronic devices. Two-dimensional electronic spectroscopy (2D-ES) is the most complete third order (χ(3)) technique, it has been shown that it is particularly useful to disentangle close-lying energy levels and to reveal dynamics in coupled molecular systems. Two different PBI covalently “head-to-tail” bound dimers (D0 and D1) with increasing interchromophoric separation, and a reference monomer (M) were synthesised and studied by means of 2D-ES in order to characterise the 1 to 2-exciton state transition and how its behaviour changes in relation to the PBI-PBI distance

Spectral Filtering as a Tool for Two-Dimensional Spectroscopy: A Theoretical Model

Two-dimensional optical spectroscopy is a powerful technique for the probing of coherent quantum superpositions. Recently, the finite width of the laser spectrum has been employed to selectively tune experiments for the study of particular coherences. This involves the exclusion of certain transition frequencies, which results in the elimination of specific Liouville pathways. The rigorous analysis of such experiments requires the use of ever more sophisticated theoretical models for the optical spectroscopy of electronic and vibronic systems. Here we develop a non-impulsive and non-Markovian model which combines an explicit definition of the laser spectrum, via the equation of motion-phase matching approach (EOM-PMA), with the hierarchical equations of motion (HEOM). This theoretical framework is capable of simulating the 2D spectroscopy of vibronic systems with low frequency modes, coupled to environments of intermediate and slower timescales. In order to demonstrate the spectral filtering of vibronic coherences, we examine the elimination of lower energy peaks fromthe 2D spectra of a zinc porphyrin monomer on blue-shifting the laser spectrum. The filtering of Liouville pathways is revealed through the disappearance of peaks from the amplitude spectra for a coupled vibrational mode

Vibrational coherences in broadband 2D electronic spectroscopy: spectral filtering vs. excited state displacement

Coherences in ultrafast 2D electronic spectroscopy (2DES) reveal superpositions of quantum states corresponding to the motion of wavepackets within the potential energy surface of molecular systems. Whilst electronic coherences imply the transfer of energy between coupled chromophores, vibrational coherences track the motion of nuclear wavepackets, with their intensities governed by the displacement of the electronic excited states with respect to the ground state equilibrium geometry. Analysis of vibrational coherences thus provides valuable information on the ground and excited state structure of molecules, with ground state bleach (GSB) and stimulated emission (SE) pathways reporting on the S0 – S1 displacement and excited state absorption (ESA) pathways also involving an S1 – Sn displacement. Recent development of broadband 2DES experiments have enabled access to a greater range of coherences involving higher energy electronic states. However, a complete analysis must consider involvement of multiple vibrational modes, and any filtering of Liouville pathways due to the finite width of the excitation spectrum. Here, combining the equation of motion-phase matching approach for finite laser spectra with the hierarchical equation of motion to correctly account for dephasing and dissipation, we model half-broadband and broadband 2DES of cresyl violet to demonstrate the impact of spectral filtering vs. the relative displacement of two excited states (S1 and Sn) on the intensity distribution of peaks in the beating maps for two vibrational modes with frequencies 350 cm-1 and 585 cm-1. This study is motivated by recent experimental results from our group which interestingly show the greatest intensity of the beating maps for the 350 cm 1 mode localised in the excited state absorption region