2,724 research outputs found
Fourier-Domain Electromagnetic Wave Theory for Layered Metamaterials of Finite Extent
The Floquet-Bloch theorem allows waves in infinite, lossless periodic media
to be expressed as a sum of discrete Floquet-Bloch modes, but its validity is
challenged under the realistic constraints of loss and finite extent. In this
work, we mathematically reveal the existence of Floquet-Bloch modes in the
electromagnetic fields sustained by lossy, finite periodic layered media using
Maxwell's equations alone without invoking the Floquet-Bloch theorem. Starting
with a transfer-matrix representation of the electromagnetic field in a generic
layered medium, we apply Fourier transformation and a series of mathematical
manipulations to isolate a term explicitly dependent on Floquet-Bloch modes.
Fourier-domain representation of the electromagnetic field can be reduced into
a product of the Floquet-Bloch term and two other matrix factors: one governed
by reflections from the medium boundaries and another dependent on layer
composition. Electromagnetic fields in any finite, lossy, layered structure can
now be interpreted in the Fourier-domain by separable factors dependent on
distinct physical features of the structure. The developed theory enables new
methods for analyzing and communicating the electromagnetic properties of
layered metamaterials.Comment: 10 pages, 3 figure
Producing a Past: Cyrus Mccormick\u27s Reaper from Heritage to History
Producing a Past explores how the false fact of Cyrus McCormick\u27s 1831 invention of the reaper came to be incorporated into the American historical cannon. From 1884 to 1932, the McCormick Harvester family and their various affiliated businesses created a useable past about their departed patriarch, Cyrus McCormick, and his role in producing civilization through advertising and the emerging historical profession. The McCormick narrative of the past which was peddled in advertising and supported in scholarship justified the family\u27s elite position in American society and its monopolistic control of the harvester industry in the face of political and popular antagonism.
As a parallel story to the McCormick\u27s hegemonic use of history, this dissertation also focuses on the professionalizing historical discipline during the Progressive Era. These early historians were anxious to demonstrate their concrete value in the corporate economy as objective guardians of the past. While ethics might have prevented them from being historians for hire, their own positions as middle-class workers pre-disposed them to be receptive to both the McCormick\u27s financial influence and their historical messages
Observation of local temporal correlations in trapped quantum gases
We measure the temporal pair correlation function of a
trapped gas of bosons above and below the critical temperature for
Bose-Einstein condensation. The measurement is performed {\it in situ} using a
local, time-resolved single-atom sensitive probing technique. Third and fourth
order correlation functions are also extracted. We develop a theoretical model
and compare it with our experimental data, finding good quantitative agreement
and highlighting the role of interactions. Our results promote temporal
correlations as new observables to study the dynamics of ultracold quantum
gases
Wellington : a novel method for the accurate identification of digital genomic footprints from DNase-seq data
The expression of eukaryotic genes is regulated by cis-regulatory elements such as promoters and enhancers, which bind sequence-specific DNA-binding proteins. One of the great challenges in the gene regulation field is to characterise these elements. This involves the identification of transcription factor (TF) binding sites within regulatory elements that are occupied in a defined regulatory context. Digestion with DNase and the subsequent analysis of regions protected from cleavage (DNase footprinting) has for many years been used to identify specific binding sites occupied by TFs at individual cis-elements with high resolution. This methodology has recently been adapted for high-throughput sequencing (DNase-seq). In this study, we describe an imbalance in the DNA strand-specific alignment information of DNase-seq data surrounding protein–DNA interactions that allows accurate prediction of occupied TF binding sites. Our study introduces a novel algorithm, Wellington, which considers the imbalance in this strand-specific information to efficiently identify DNA footprints. This algorithm significantly enhances specificity by reducing the proportion of false positives and requires significantly fewer predictions than previously reported methods to recapitulate an equal amount of ChIP-seq data. We also provide an open-source software package, pyDNase, which implements the Wellington algorithm to interface with DNase-seq data and expedite analyses
Millimeter-long Fiber Fabry-Perot cavities
We demonstrate fiber Fabry-Perot (FFP) cavities with concave mirrors that can
be operated at cavity lengths as large as 1.5mm without significant
deterioration of the finesse. This is achieved by using a laser dot machining
technique to shape spherical mirrors with ultralow roughness and employing
single-mode fibers with large mode area for good mode matching to the cavity.
Additionally, in contrast to previous FFPs, these cavities can be used over an
octave-spanning frequency range with adequate coatings. We also show directly
that shape deviations caused by the fiber's index profile lead to a finesse
decrease as observed in earlier attempts to build long FFP cavities, and show a
way to overcome this problem
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