599 research outputs found
Reactivation of the mitosis-promoting factor in postmitotic cardiomyocytes
Cardiomyocytes cease to divide shortly after birth and an irreversible cell cycle arrest is evident accompanied by the downregulation of cyclin-dependent kinase activities. To get a better understanding of the cardiac cell cycle and its regulation, the effect of functional recovery of the mitosis-promoting factor (MPF) consisting of cyclin B1 and the cyclin-dependent kinase Cdc2 was assessed in primary cultures of postmitotic ventricular adult rat cardiomyocytes ( ARC). Gene transfer into ARC was achieved using the adenovirus-enhanced transferrinfection system that was characterized by the absence of cytotoxic events. Simultaneous ectopic expression of wild-type versions of cyclin B1 and Cdc2 was sufficient to induce MPF activity. Reestablished MPF resulted in a mitotic phenotype, marked by an abnormal condensation of the nuclei, histone H3 phosphorylation and variable degree of decay of the contractile apparatus. Although a complete cell division was not observed, the results provided conclusive evidence that cell cycle-related events in postmitotic cardiomyocytes could be triggered by genetic intervention downstream of the G1/S checkpoint. This will be of importance to design novel strategies to overcome the proliferation arrest in adult cardiomyocytes
Two-photon interference with two independent pseudo-thermal sources
The nature of two-photon interference is a subject that has aroused renewed
interest in recent years and is still under debate. In this paper we report the
first observation of two-photon interference with independent pseudo-thermal
sources in which sub-wavelength interference is observed. The phenomenon may be
described in terms of the classical statistical distribution of the two sources
and their optical transfer functions.Comment: Phys. Rev. A 74, 053807 (2006
Fabrication of Thin, Luminescent, Single-crystal Diamond Membranes
The formation of single-crystal diamond membranes is an important
prerequisite for the fabrication of high-quality optical cavities in this
material. Diamond membranes fabricated using lift-off processes involving the
creation of a damaged layer through ion implantation often suffer from residual
ion damage, which severely limits their usefulness for photonic structures. The
current work demonstrates that strategic etch removal of the most highly
defective material yields thin, single-crystal diamond membranes with strong
photoluminescence and a Raman signature approaching that of single-crystal bulk
diamond. These optically-active membranes can form the starting point for
fabrication of high-quality optical resonators.Comment: To appear in AP
Mask formulas for cograssmannian Kazhdan-Lusztig polynomials
We give two contructions of sets of masks on cograssmannian permutations that
can be used in Deodhar's formula for Kazhdan-Lusztig basis elements of the
Iwahori-Hecke algebra. The constructions are respectively based on a formula of
Lascoux-Schutzenberger and its geometric interpretation by Zelevinsky. The
first construction relies on a basis of the Hecke algebra constructed from
principal lower order ideals in Bruhat order and a translation of this basis
into sets of masks. The second construction relies on an interpretation of
masks as cells of the Bott-Samelson resolution. These constructions give
distinct answers to a question of Deodhar.Comment: 43 page
Coupling of silicon-vacancy centers to a single crystal diamond cavity
Optical coupling of an ensemble of silicon-vacancy (SiV) centers to
single-crystal diamond microdisk cavities is demonstrated. The cavities are
fabricated from a single-crystal diamond membrane generated by ion implantation
and, electrochemical liftoff followed by homo-epitaxial overgrowth. Whispering
gallery modes which spectrally overlap with the zero-phonon line (ZPL) of the
SiV centers and exhibit quality factors ~2200 are measured. Lifetime reduction
from 1.8 ns to 1.48 ns is observed from SiV centers in the cavity compared to
those in the membrane outside the cavity. These results are pivotal in
developing diamond integrated photonics networks
Deterministic coupling of delta-doped NV centers to a nanobeam photonic crystal cavity
The negatively-charged nitrogen vacancy center (NV) in diamond has generated
significant interest as a platform for quantum information processing and
sensing in the solid state. For most applications, high quality optical
cavities are required to enhance the NV zero-phonon line (ZPL) emission. An
outstanding challenge in maximizing the degree of NV-cavity coupling is the
deterministic placement of NVs within the cavity. Here, we report photonic
crystal nanobeam cavities coupled to NVs incorporated by a delta-doping
technique that allows nanometer-scale vertical positioning of the emitters. We
demonstrate cavities with Q up to ~24,000 and mode volume V ~
as well as resonant enhancement of the ZPL of an NV
ensemble with Purcell factor of ~20. Our fabrication technique provides a first
step towards deterministic NV-cavity coupling using spatial control of the
emitters.Comment: 13 pages, 3 figure
Deterministic coupling of delta-doped nitrogen vacancy centers to a nanobeam photonic crystal cavity
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