719 research outputs found
Sharp entanglement thresholds in the logarithmic negativity of disjoint blocks in the transverse-field Ising chain
Entanglement has developed into an essential concept for the characterization
of phases and phase transitions in ground states of quantum many-body systems.
In this work, we use the logarithmic negativity to study the spatial
entanglement structure in the transverse-field Ising chain both in the ground
state and at nonzero temperatures. Specifically, we investigate the
entanglement between two disjoint blocks as a function of their separation,
which can be viewed as the entanglement analog of a spatial correlation
function. We find sharp entanglement thresholds at a critical distance beyond
which the logarithmic negativity vanishes exactly and thus the two blocks
become unentangled, which holds even in the presence of long-ranged quantum
correlations, i.e., at the system's quantum critical point. Using Time-Evolving
Block Decimation (TEBD), we explore this feature as a function of temperature
and size of the two blocks and present a simple model to describe our numerical
observations.Comment: 12 pages, 7 figure
Polarization Evolution in Strong Magnetic Fields
Extremely strong magnetic fields change the vacuum index of refraction.
Although this polarization dependent effect is small for typical neutron stars,
it is large enough to decouple the polarization states of photons traveling
within the field. The photon states evolve adiabatically and follow the
changing magnetic field direction. The combination of a rotating magnetosphere
and a frequency dependent state decoupling predicts polarization phase lags
between different wave bands, if the emission process takes place well within
the light cylinder. This QED effect may allow observations to distinguish
between different pulsar emission mechanisms and to reconstruct the structure
of the magnetosphere.Comment: 22 pages, 10 figures, accepted for publication in MNRA
See a Black Hole on a Shoestring
The modes of vibration of hanging and partially supported strings provide
useful analogies to scalar fields travelling through spacetimes that admit
conformally flat spatial sections. This wide class of spacetimes includes
static, spherically symmetric spacetimes. The modes of a spacetime where the
scale factor depends as a power-law on one of the coordinates provide a useful
starting point and yield a new classification of these spacetimes on the basis
of the shape of the string analogue. The family of corresponding strings follow
a family of curves related to the cycloid, denoted here as hypercycloids (for
reasons that will become apparent). Like the spacetimes that they emulate these
strings exhibit horizons, typically at their bottommost points where the string
tension vanishes; therefore, hanging strings may provide a new avenue for the
exploration of the quantum mechanics of horizons.Comment: 5 pages, 1 figure, extensive changes to refect version accepted to
PR
In vitro recombination cloning of entire cDNA libraries in Arabidopsis thaliana and its application to the yeast two-hybrid system
In the postgenomic era many experiments rely on the availability of transcript sequence for cloning. As these clones usually originate from cDNA libraries, the quality of these libraries is crucial. If a good library is generated it is desirable to use a versatile cloning system suitable for many different kinds of applications. The cloning systems based on in vitro recombination proves fitting for this task. However, the use of this method for shuttling entire cDNA libraries between different vectors has not yet been studied in great detail. Here we describe the construction of four cDNA libraries from different tissues of Arabidopsis thaliana, the shuttling of the libraries into expression vectors, and evaluation of this method as well as its suitability for downstream applications. Libraries were constructed from seedlings, hormone treated seedlings, flowers, developing seeds and primary leaves in the ldquoentry vectorrdquo of the Gatewaytrade cloning system. After initial characterization of the libraries, they were shuttled into an expression vector (a yeast two-hybrid prey vector). To monitor for a size bias generally assumed to be inherent to in vitro recombination methods, the libraries were characterized before and after the transfer into the expression vector. However no significant difference could be detected. The functionality of the in vitro recombination system for the shuttling of entire libraries was then further tested by protein-protein interaction screens. The results of the library characterization and of the yeast two-hybrid screens and their implications for large-scale proteomic approaches are discussed
Handling and analysis of ices in cryostats and glove boxes in view of cometary samples
Comet nucleus sample return mission and other return missions from planets and satellites need equipment for handling and analysis of icy samples at low temperatures under vacuum or protective gas. Two methods are reported which were developed for analysis of small icy samples and which are modified for larger samples in cometary matter simulation experiments (KOSI). A conventional optical cryostat system was modified to allow for transport of samples at 5 K, ion beam irradiation, and measurement in an off-line optical spectrophotometer. The new system consists of a removable window plug containing nozzles for condensation of water and volatiles onto a cold finger. This plug can be removed in a vacuum system, changed against another plug (e.g., with other windows (IR, VIS, VUV) or other nozzles). While open, the samples can be treated under vacuum with cooling by manipulators (cut, removal, sample taking, irradiation with light, photons, or ions). After bringing the plug back, the samples can be moved to another site of analysis. For handling the 30 cm diameter mineral-ice samples from the KOSI experiments an 80x80x80 cm glove box made out of plexiglass was used. The samples were kept in a liquid nitrogen bath, which was filled from the outside. A stream a dry N2 and evaporating gas from the bath purified the glove box from impurity gases and, in particular, H2O, which otherwise would condense onto the samples
Magnetically Catalyzed Fusion
We calculate the reaction cross-sections for the fusion of hydrogen and
deuterium in strong magnetic fields as are believed to exist in the atmospheres
of neutron stars. We find that in the presence of a strong magnetic field (B
\gsim 10^{12}G), the reaction rates are many orders of magnitude higher than
in the unmagnetized case. The fusion of both protons and deuterons are
important over a neutron star's lifetime for ultrastrong magnetic fields (G). The enhancement may have dramatic effects on thermonuclear
runaways and bursts on the surfaces of neutron stars.Comment: 13 pages, 6 figure
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