791 research outputs found
Size dependent tunneling and optical spectroscopy of CdSe quantum rods
Photoluminescence excitation spectroscopy and scanning tunneling spectroscopy
are used to study the electronic states in CdSe quantum rods that manifest a
transition from a zero dimensional to a one dimensional quantum confined
structure. Both optical and tunneling spectra show that the level structure
depends primarily on the rod diameter and not on length. With increasing
diameter, the band-gap and the excited state level spacings shift to the red.
The level structure was assigned using a multi-band effective-mass model,
showing a similar dependence on rod dimensions.Comment: Accepted to PRL (nearly final version). 4 pages in revtex, 4 figure
Construction of one-loop SYM effective action on the mixed branch in the harmonic superspace approach
We develop a systematic approach to construct the one-loop SYM
effective action depending on both vector multiplet and
hypermultiplet background fields. Beginning with the formulation of SYM theory in terms of harmonic superfields, we construct
the one-loop effective action using the covariant harmonic
supergraphs and calculate it in harmonic superfield form for
constant Abelian strength and corresponding constant hypermultiplet
fields. The hypermultiplet-dependent effective action is derived and given by
integral over the analytic subspace of harmonic superspace. We show that each
term in the Schwinger-De Witt expansion of the low-energy effective action is
written as integral over full superspace.Comment: 35 pages, JHEP styl
Higher order contributions to the effective action of N=2 super Yang-Mills
We apply heat kernel techniques in N=1 superspace to compute the one-loop
effective action to order for chiral superfields coupled to a non-Abelian
super Yang-Mills background. The results, when combined with those of
hep-th/0210146, yield the one-loop effective action to order for any N=2
super Yang-Mills theory coupled to matter hypermultiplets.Comment: 23 pages, references adde
Optimizing the photoassociation of cold atoms by use of chirped laser pulses
Photoassociation of ultracold atoms induced by chirped picosecond pulses is
analyzed in a non-perturbative treatment by following the wavepackets dynamics
on the ground and excited surfaces. The initial state is described by a
Boltzmann distribution of continuum scattering states. The chosen example is
photoassociation of cesium atoms at temperature T=54 from the continuum to bound levels in the external well of the
potential. We study how the modification of the pulse
characteristics (carrier frequency, duration, linear chirp rate and intensity)
can enhance the number of photoassociated molecules and suggest ways of
optimizing the production of stable molecules.Comment: 40 pages, 12 figures, submitted to Eur. Phys. J.
Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules
Coupled colloidal quantum dot molecules (CQDMs) are an emerging class of nanomaterials, manifesting two coupled emission centers and thus introducing additional degrees of freedom for designing quantum-dot-based technologies. The properties of multiply excited states in these CQDMs are crucial to their performance as quantum light emitters, but they cannot be fully resolved by existing spectroscopic techniques. Here we study the characteristics of biexcitonic species, which represent a rich landscape of different configurations essentially categorized as either segregated or localized biexciton states. To this end, we introduce an extension of Heralded Spectroscopy to resolve the different biexciton species in the prototypical CdSe/CdS CQDM system. By comparing CQDMs with single quantum dots and with nonfused quantum dot pairs, we uncover the coexistence and interplay of two distinct biexciton species: A fast-decaying, strongly interacting biexciton species, analogous to biexcitons in single quantum dots, and a long-lived, weakly interacting species corresponding to two nearly independent excitons. The two biexciton types are consistent with numerical simulations, assigning the strongly interacting species to two excitons localized at one side of the quantum dot molecule and the weakly interacting species to excitons segregated to the two quantum dot molecule sides. This deeper understanding of multiply excited states in coupled quantum dot molecules can support the rational design of tunable single- or multiple-photon quantum emitters.U.B. and D.O. acknowledge the support of the Israel Science Foundation (ISF) and the Directorate for Defense Research and Development (DDR&D), grant No. 3415/21. J.I.C. and J.P. acknowledge support from UJI project B-2021-06. E.S., A.L., Y.E.P., and Y.O. acknowledge support from the Hebrew University Center for Nanoscience and Nanotechnology
The Effect of Cone Opsin Mutations on Retinal Structure and the Integrity of the Photoreceptor Mosaic
Purpose.
To evaluate retinal structure and photoreceptor mosaic integrity in subjects with OPN1LW and OPN1MW mutations.
Methods.
Eleven subjects were recruited, eight of whom have been previously described. Cone and rod density was measured using images of the photoreceptor mosaic obtained from an adaptive optics scanning light ophthalmoscope (AOSLO). Total retinal thickness, inner retinal thickness, and outer nuclear layer plus Henle fiber layer (ONL+HFL) thickness were measured using cross-sectional spectral-domain optical coherence tomography (SD-OCT) images. Molecular genetic analyses were performed to characterize the OPN1LW/OPN1MW gene array.
Results.
While disruptions in retinal lamination and cone mosaic structure were observed in all subjects, genotype-specific differences were also observed. For example, subjects with “L/M interchange” mutations resulting from intermixing of ancestral OPN1LW and OPN1MW genes had significant residual cone structure in the parafovea (∼25% of normal), despite widespread retinal disruption that included a large foveal lesion and thinning of the parafoveal inner retina. These subjects also reported a later-onset, progressive loss of visual function. In contrast, subjects with the C203R missense mutation presented with congenital blue cone monochromacy, with retinal lamination defects being restricted to the ONL+HFL and the degree of residual cone structure (8% of normal) being consistent with that expected for the S-cone submosaic.
Conclusions.
The photoreceptor phenotype associated with OPN1LW and OPN1MW mutations is highly variable. These findings have implications for the potential restoration of visual function in subjects with opsin mutations. Our study highlights the importance of high-resolution phenotyping to characterize cellular structure in inherited retinal disease; such information will be critical for selecting patients most likely to respond to therapeutic intervention and for establishing a baseline for evaluating treatment efficacy
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