1,540 research outputs found
Chromosome condensation in mitosis and meiosis of rye (Secale cereale L.)
Structural investigation and morphometry of meiotic chromosomes by scanning electron microscopy (in comparison to light microscopy) of all stages of condensation of meiosis I + II show remarkable differences during chromosome condensation in mitosis and meiosis I of rye (Secale cereale) with respect to initiation, mode and degree of condensation. Mitotic chromosomes condense in a linear fashion, shorten in length and increase moderately in diameter. In contrast, in meiosis I, condensation of chromosomes in length and diameter is a sigmoidal process with a retardation in zygotene and pachytene and an acceleration from diplotene to diakinesis. The basic structural components of mitotic chromosomes of rye are ``parallel fibers{''} and ``chromomeres{''} which become highly compacted in metaphase. Although chromosome architecture in early prophase of meiosis seems similar to mitosis in principle, there is no equivalent stage during transition to metaphase I when chromosomes condense to a much higher degree and show a characteristic ``smooth{''} surface. No indication was found for helical winding of chromosomes either in mitosis or in meiosis. Based on measurements, we propose a mechanism for chromosome dynamics in mitosis and meiosis, which involves three individual processes: (i) aggregation of chromatin subdomains into a chromosome filament, (ii) condensation in length, which involves a progressive increase in diameter and (iii) separation of chromatids. Copyright (C) 2003 S. Karger AG, Basel
Ultrastructural analysis of chromatin in meiosis I plus II of rye (Secale cereale L.)
Scanning electron microscopy (SEM) proves to be an appropriate technique for imaging chromatin organization in meiosis I and II of rye (Secale cereale) down to a resolution of a few nanometers. It could be shown for the first time that organization of basic structural elements (coiled and parallel fibers, chromomeres) changes dramatically during the progression to metaphase I and II. Controlled loosening with proteinase K (after fixation with glutaraldehyde) provides an enhanced insight into chromosome architecture even of highly condensed stages of meiosis. By selective staining with platinum blue, DNA content and distribution can be visualized within compact chromosomes as well as in a complex arrangement of fibers. Chromatin interconnecting threads, which are typically observed in prophase I between homologous and non-homologous chromosomes, stain clearly for DNA. In zygotene transversion of chromatid strands to their homologous counterparts becomes evident. In pachytene segments of synapsed and non-synapsed homologs alternate. At synapsed regions pairing is so intimate that homologous chromosomes form one filament of structural entity. Chiasmata are characterized by chromatid strands which traverse from one homolog to its counterpart. Bivalents are characteristically fused at their telomeric regions. In metaphase I and II there is no structural evidence for primary and secondary constrictions. Copyright (C) 2003 S. Karger AG, Basel
Motion Tomography of a single trapped ion
A method for the experimental reconstruction of the quantum state of motion
for a single trapped ion is proposed. It is based on the measurement of the
ground state population of the trap after a sudden change of the trapping
potential. In particular, we show how the Q function and the quadrature
distribution can be measured directly. In an example we demonstrate the
principle and analyze the sensibility of the reconstruction process to
experimental uncertainties as well as to finite grid limitations. Our method is
not restricted to the Lamb-Dicke Limit and works in one or more dimensions.Comment: 4 pages, Revtex format, 4 postscript figures, changed typographical
error
Synthetic Helical Liquids with Ultracold Atoms in Optical Lattices
We discuss a platform for the synthetic realization of key physical
properties of helical Tomonaga Luttinger liquids (HTLLs) with ultracold
fermionic atoms in one-dimensional optical lattices. The HTLL is a strongly
correlated metallic state where spin polarization and propagation direction of
the itinerant particles are locked to each other. We propose an unconventional
one-dimensional Fermi-Hubbard model which, at quarter filling, resembles the
HTLL in the long wavelength limit, as we demonstrate with a combination of
analytical (bosonization) and numerical (density matrix renormalization group)
methods. An experimentally feasible scheme is provided for the realization of
this model with ultracold fermionic atoms in optical lattices. Finally, we
discuss how the robustness of the HTLL against back-scattering and
imperfections, well known from its realization at the edge of two-dimensional
topological insulators, is reflected in the synthetic one-dimensional scenario
proposed here
Absorption in Ultra-Peripheral Nucleus-Atom Collisions in Crystal
The Glauber theory description of particle- and nucleus-crystal Coulomb
interactions at high-energy is developed. The allowance for the lattice thermal
vibrations is shown to produce strong absorption effect which is of prime
importance for quantitative understanding of the coherent Coulomb excitation of
ultra-relativistic particles and nuclei passing through the crystal.Comment: 8 pages, LaTe
Strong coupling of a mechanical oscillator and a single atom
We propose and analyze a setup to achieve strong coupling between a single
trapped atom and a mechanical oscillator. The interaction between the motion of
the atom and the mechanical oscillator is mediated by a quantized light field
in a laser driven high-finesse cavity. In particular, we show that high
fidelity transfer of quantum states between the atom and the mechanical
oscillator is in reach for existing or near future experimental parameters. Our
setup provides the basic toolbox for coherent manipulation, preparation and
measurement of micro- and nanomechanical oscillators via the tools of atomic
physics.Comment: 4 pages, 2 figures, minro changes, accepted by PR
Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency
We demonstrate theoretically a parallelized C-NOT gate which allows to
entangle a mesoscopic ensemble of atoms with a single control atom in a single
step, with high fidelity and on a microsecond timescale. Our scheme relies on
the strong and long-ranged interaction between Rydberg atoms triggering
Electromagnetically Induced Transparency (EIT). By this we can robustly
implement a conditional transfer of all ensemble atoms among two logical
states, depending on the state of the control atom. We outline a many body
interferometer which allows a comparison of two many-body quantum states by
performing a measurement of the control atom.Comment: published versio
Repulsively bound atom pairs: Overview, Simulations and Links
We review the basic physics of repulsively bound atom pairs in an optical
lattice, which were recently observed in the laboratory, including the theory
and the experimental implementation. We also briefly discuss related many-body
numerical simulations, in which time-dependent Density Matrix Renormalisation
Group (DMRG) methods are used to model the many-body physics of a collection of
interacting pairs, and give a comparison of the single-particle quasimomentum
distribution measured in the experiment and results from these simulations. We
then give a short discussion of how these repulsively bound pairs relate to
bound states in some other physical systems.Comment: 7 pages, 3 figures, Proceedings of ICAP-2006 (Innsbruck
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