3,427 research outputs found
On an easy transition from operator dynamics to generating functionals by Clifford algebras
Clifford geometric algebras of multivectors are treated in detail. These
algebras are build over a graded space and exhibit a grading or multivector
structure. The careful study of the endomorphisms of this space makes it clear,
that opposite Clifford algebras have to be used also. Based on this
mathematics, we give a fully Clifford algebraic account on generating
functionals, which is thereby geometric. The field operators are shown to be
Clifford and opposite Clifford maps. This picture relying on geometry does not
need positivity in principle. Furthermore, we propose a transition from
operator dynamics to corresponding generating functionals, which is based on
the algebraic techniques. As a calculational benefit, this transition is
considerable short compared to standard ones. The transition is not injective
(unique) and depends additionally on the choice of an ordering. We obtain a
direct and constructive connection between orderings and the explicit form of
the functional Hamiltonian. These orderings depend on the propagator of the
theory and thus on the ground state. This is invisible in path integral
formulations. The method is demonstrated within two examples, a non-linear
spinor field theory and spinor QED. Antisymmetrized and normal-ordered
functional equations are derived in both cases.Comment: 23p., 76kB, plain LaTeX, [email protected]
Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots
The spectra of two-dimensional photonic crystal slab nanocavities with
embedded InAs quantum dots are measured by photoluminescence and reflectance.
In comparing the spectra taken by these two different methods, consistency with
the nanocavities' resonant wavelengths is found. Furthermore, it is shown that
the reflectance method can measure both active and passive cavities. Q-factors
of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are
measured by the reflectance method in cross polarization. Experimentally,
Q-factors decrease for longer wavelengths and the intensity, reflected by the
nanocavities on resonance, becomes minimal around 1370 nm. The trend of the
Q-factors is explained by the change of the slab thickness relative to the
resonant wavelength, showing a good agreement between theory and experiment.
The trend of reflected intensity by the nanocavities on resonance can be
understood as effects that originate from the PC slab and the underlying air
cladding thickness. In addition to three dimensional finite-difference
time-domain calculations, an analytical model is introduced that is able to
reproduce the wavelength dependence of the reflected intensity observed in the
experiment.Comment: 24 pages, 7 figures, corrected+full versio
The search for planetary mass companions to field brown dwarfs with HST/NICMOS
We present the results of a high-resolution spectral differential imaging
survey of 12 nearby, relatively young field L dwarfs (<1 Gyr) carried out with
HST/NICMOS to search for planetary mass companions at small physical
separations from their host. The survey resolved two brown dwarf binaries: the
L dwarf system Kelu-1AB and the newly discovered L/T transition system 2MASS
J031059+164815AB. For both systems common proper motion has already been
confirmed in follow-up observations which have been published elsewhere. The
derived separations of the binaries are smaller than 6 AU and consistent with
previous brown dwarf binary statistics. Their mass ratios of q > 0.8 confirm
the preference for equal mass systems similar to a large number of other
surveys. Furthermore, we found tentative evidence for a companion to the L4
dwarf 2MASS W033703-175807, straddling the brown dwarf/planetary mass boundary
and revealing an uncommonly low mass ratio system (q ~ 0.2) compared to the
vast majority of previously found brown dwarf binaries. With a derived minimum
mass of 10 - 15 Mjup, a planetary nature of the secondary cannot be ruled out
yet. However, it seems more likely to be a very low mass brown dwarf secondary
at the border of the spectral T/Y transition regime, primarily due to its
similarities to recently found very cool T dwarfs. This would make it one of
the closest resolved brown dwarf binaries (0.087" 0.015", corresponding
to 2.52 0.44 AU at a distance of 29 pc) with the coolest (Teff ~ 600-630
K) and least massive companion to any L or T dwarf.Comment: 33 pages, 8 figures, 2 tables, accepted for publication by Ap
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Eye-tracking Film Music
Film music scholars, composers, directors and audiences have always implicitly believed that music can help determine the focus of an audienceâs visual attention, but researchers have not as yet been able to prove this empirically. Eye-tracking researchâthe process of measuring either the point of gaze or the motion of the eyesâhas grown exponentially in recent years. This paper reports on a foundational, empirical eye-tracking study that examined the effects of contextual musical attributes on visual attention, emotion and user experience during exploration tasks in moving images. Our results show that music is able to direct how we see by switching attention to target foci more quickly as well as lengthening fixations, and that music can also encourage greater exploration of visual scenes outside targets. Our work contributes the first step in understanding how music shapes visual attention using eye-tracking techniques. We encourage wider adoption of this approach which has the potential to enhance understanding of the complex processes of audiovisual perception in action
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Investigating the Intelligibility of a Computer Vision System for Blind Users
Computer vision systems to help blind usersare becoming increasingly common yet often these systems are not intelligible. Our work investigates the intelligibility of a wearable computer vision system to help blind users locate and identify people in their vicinity. Providing a continuous stream of information, this system allows us to explore intelligibility through interaction and instructions, going beyond studies of intelligibility that focus on explaining a decision a computer vision system might make. In a study with 13 blind users, we explored whether varying instructions (either basic or enhanced) about how the system worked would change blind usersâ experience of the system. We found offering a more detailed set of instructions did not affect how successful users were using the system nor their perceived workload. We did, however, find evidence of significant differences in what they knew about the system, and they employed different, and potentially more effective, use strategies. Our findings have important implications for researchers and designers of computer vision systemsfor blind users, as well more general implications for understanding what it means to make interactive computer vision systems intelligible
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XAI-Explainable artificial intelligence
Explainability is essential for users to effectively understand, trust, and manage powerful artificial intelligence applications
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