2,477 research outputs found
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
Rotational cooling of trapped polyatomic molecules
Controlling the internal degrees of freedom is a key challenge for
applications of cold and ultracold molecules. Here, we demonstrate
rotational-state cooling of trapped methyl fluoride molecules (CH3F) by
optically pumping the population of 16 M-sublevels in the rotational states
J=3,4,5, and 6 into a single level. By combining rotational-state cooling with
motional cooling, we increase the relative number of molecules in the state
J=4, K=3, M=4 from a few percent to over 70%, thereby generating a
translationally cold (~30mK) and nearly pure state ensemble of about 10^6
molecules. Our scheme is extendable to larger sets of initial states, other
final states and a variety of molecule species, thus paving the way for
internal-state control of ever larger molecules
Analysis of Sedimentary Facies Using Bulk Mineralogic Characteristics in Cretaceous to Quaternary Sediments from the Kerguelen Plateau: Sites 737, 738, and 744
Carbonate-free portions of Upper Cretaceous to Holocene sediment samples from the Kerguelen Plateau in the
southern Indian Ocean were investigated by X-ray diffraction. Downhole variations in the content of opal-A, opal-CT,
quartz, feldspar, barite, and clinoptilolite were studied at Site 737 on the northern Kerguelen Plateau and at Sites 744
and 738 on the southern Kerguelen Plateau. The variation of these components reflects temporal changes in the depositional
history of the Kerguelen Plateau as well as major differences in the sedimentary evolution between the northern
plateau and the southern plateau.
Carbonate is the dominant component in the pelagic sediments on the Kerguelen Plateau. In addition, biogenic opal
sedimentation plays an important role throughout most of the sequence. A major increase in opal accumulation is documented
at all sites in late Miocene time, which is in accordance with the well-known increase in silica productivity
probably caused by a major cooling step. Because of its position near the Polar Frontal Zone, sediments from Site 737
show a more extensive opal deposition than at Sites 744 and 738. An earlier productivity pulse is documented at Site 744
on the southern plateau within the early Oligocene, following the initial phase of intense East Antarctic glaciation. This
cooling event resulted in higher amounts of ice-rafted terrigenous quartz and, to a lesser extent, feldspar. With the exception
of the Site 744 sediments, opal deposition in Paleogene and older sediments can be reconstructed only from the
diagenetic transformation products of opal-CT and probably clinoptilolite. In contrast to the southern sequence, on the
northern Kerguelen Plateau higher amounts of clinoptilolite and no opal-CT were found. These major differences in the
diagenetic environments may be due to extensive volcanism in the northern area. The volcanic influence at Site 737 is
well recorded by the higher feldspar content and higher amounts of volcanic glass shards
Expropriation in the Simple Cadastre
In this paper we investigate the necessary interaction between expropriation and the cadastre. We investigate first the role of expropriation in modern society and the stake holders and then analyze the interaction with land registration and cadastre. The "simple cadastre" framework allows a treatment independent of national particulars. A simple cadastre is a minimal model that satisfies the needs of the users of the cadastre and abstracts from non-essential aspects, any national legislation is full of. In this paper we investigate how a cadastre supports expropriation and what the necessary interface is. We conclude that the expropriation procedures need access to registration data and a process to register a transfer of ownership effectuated by a court judgment, but no special arrangements that would only serve expropriation procedures
Spinon excitations in the XX chain: spectra, transition rates, observability
The exact one-to-one mapping between (spinless) Jordan-Wigner lattice
fermions and (spin-1/2) spinons is established for all eigenstates of the
one-dimensional s = 1=2 XX model on a lattice with an even or odd number N of
lattice sites and periodic boundary conditions. Exact product formulas for the
transition rates derived via Bethe ansatz are used to calculate asymptotic
expressions of the 2-spinon and 4-spinon parts (for large even N) as well as of
the 1-spinon and 3-spinon parts (for large odd N) of the dynamic spin structure
factors. The observability of these spectral contributions is assessed for
finite and infinite N.Comment: 19 pages, 10 figure
Violation of the `Zero-Force Theorem' in the time-dependent Krieger-Li-Iafrate approximation
We demonstrate that the time-dependent Krieger-Li-Iafrate approximation in
combination with the exchange-only functional violates the `Zero-Force
Theorem'. By analyzing the time-dependent dipole moment of Na5 and Na9+, we
furthermore show that this can lead to an unphysical self-excitation of the
system depending on the system properties and the excitation strength.
Analytical aspects, especially the connection between the `Zero-Force Theorem'
and the `Generalized-Translation Invariance' of the potential, are discussed.Comment: 5 pages, 4 figure
The old and heavy bulge of M31 I. Kinematics and stellar populations
We present new optical long-slit data along 6 position angles of the bulge
region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin
from the center, where the disk light contribution is always less than 30%, and
out to 8 arcmin along the major axis, where the disk makes 55% of the total
light. We show that the velocity dispersions of McElroy (1983) are severely
underestimated (by up to 50 km/s) and previous dynamical models have
underestimated the stellar mass of M31's bulge by a factor 2. Moreover, the
light-weighted velocity dispersion of the galaxy grows to 166 km/s, thus
reducing the discrepancy between the predicted and measured mass of the black
hole at the center of M31. The kinematic position angle varies with distance,
pointing to triaxiality. We detect gas counterrotation near the bulge minor
axis. We measure eight emission-corrected Lick indices. They are approximately
constant on circles. We derive the age, metallicity and alpha-element
overabundance profiles. Except for the region in the inner arcsecs of the
galaxy, the bulge of M31 is uniformly old (>12 Gyr, with many best-fit ages at
the model grid limit of 15 Gyr), slightly alpha-elements overabundant
([alpha/Fe]~0.2) and at solar metallicity, in agreement with studies of the
resolved stellar components. The predicted u-g, g-r and r-i Sloan color
profiles match reasonably well the dust-corrected observations. The stellar
populations have approximately radially constant mass-to-light ratios (M/L_R ~
4-4.5 for a Kroupa IMF), in agreement with stellar dynamical estimates based on
our new velocity dispersions. In the inner arcsecs the luminosity-weighted age
drops to 4-8 Gyr, while the metallicity increases to above 3 times the solar
value.Comment: Accepted for publication in A&
Dissociation of Feshbach Molecules into Different Partial Waves
Ultracold molecules can be associated from ultracold atoms by ramping the
magnetic field through a Feshbach resonance. A reverse ramp dissociates the
molecules. Under suitable conditions, more than one outgoing partial wave can
be populated. A theoretical model for this process is discussed here in detail.
The model reveals the connection between the dissociation and the theory of
multichannel scattering resonances. In particular, the decay rate, the
branching ratio, and the relative phase between the partial waves can be
predicted from theory or extracted from experiment. The results are applicable
to our recent experiment in 87Rb, which has a d-wave shape resonance.Comment: Added Refs.[32-38
Constant Infusions vs. Intermittent Doses of Gentamicin Against Pseudomonas aeruginosa in Vitro
Comparative studies were performed in vitro to test the advocated superiority of infusion over intermittent injection of aminoglycosides. Pseudomonas aeruginosa was exposed to constant and to continuously decreasing (simulating in vivo kinetics) concentrations of gentamicin. In comparing the effect with similar area-under-the-concentration-vs.-time curves, a substantial difference in killing and regrowth could not be demonstrated. Regrowth occurred only when the gentamicin concentration had continuously decreased below one fourth of the minimal inhibitory concentration for > 2 hr. Exposure of P. aeruginosa to gentamicin for 30 min was followed by persistent suppression of bacterial regrowth for 1.4-1.9 hr. Thus, intermittent exposure of P. aeruginosa to gentamicin is as effective as constant exposure in vitro. The demonstrated persistent postantibiotic effect might cover in part the periods between intermittent doses of gentamicin in vivo as well as in vitr
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