4,011 research outputs found
Transition rates via Bethe ansatz for the spin-1/2 Heisenberg chain
We use the exact determinantal representation derived by Kitanine, Maillet,
and Terras for matrix elements of local spin operators between Bethe wave
functions of the one-dimensional s=1/2 Heisenberg model to calculate and
numerically evaluate transition rates pertaining to dynamic spin structure
factors. For real solutions z_1,...,z_r of the Bethe ansatz equations, the size
of the determinants is of order r x r. We present applications to the
zero-temperature spin fluctuations parallel and perpendicular to an external
magnetic field.Comment: 4 pages, 4 figures and LaTeX-svjour clas
Yield and quality of potato tubers: Effects of different intensity and kind of manuring (biodynamic or organic)
Biodynamic farming is the oldest organic farming movement in Germany. Since Dr. Rudolf Steiner’s “Course on Agriculture” held in 1924, the number of biodynamic farmers in Germany has grown continuously, with 1,317 farmers currently producing on 47,592 ha. One of the most distinctive aspects of biodynamic farming is the use of the so-called biodynamic preparations, which are applied in homeopathic doses. Biodynamic preparations are supposed to improve plant growth and food quality, minimising natural variations. This paper deals with investigations of influences of these preparations and increased manure application on potato yield and tuber quality. The results are drawn from extensive research on organic potato production carried out by several institutes of the University of Bonn, sponsored by the Deutsche Forschungsgemeinschaft (Bonn), and the Eden Foundation (Bad Soden)
Single-Photon Switch based on Rydberg Blockade
All-optical switching is a technique in which a gate light pulse changes the
transmission of a target light pulse without the detour via electronic signal
processing. We take this to the quantum regime, where the incoming gate light
pulse contains only one photon on average. The gate pulse is stored as a
Rydberg excitation in an ultracold atomic gas using electromagnetically induced
transparency. Rydberg blockade suppresses the transmission of the subsequent
target pulse. Finally, the stored gate photon can be retrieved. A retrieved
photon heralds successful storage. The corresponding postselected subensemble
shows an extinction of 0.05. The single-photon switch offers many interesting
perspectives ranging from quantum communication to quantum information
processing
Single-Photon Transistor Using a F\"orster Resonance
An all-optical transistor is a device in which a gate light pulse switches
the transmission of a target light pulse with a gain above unity. The gain
quantifies the change of the transmitted target photon number per incoming gate
photon. We study the quantum limit of one incoming gate photon and observe a
gain of 20. The gate pulse is stored as a Rydberg excitation in an ultracold
gas. The transmission of the subsequent target pulse is suppressed by Rydberg
blockade which is enhanced by a F\"orster resonance. The detected target
photons reveal in a single shot with a fidelity above 0.86 whether a Rydberg
excitation was created during the gate pulse. The gain offers the possibility
to distribute the transistor output to the inputs of many transistors, thus
making complex computational tasks possible
Modeling and experimental investigations of the stress-softening behavior of soft collagenous tissues
This paper deals with the formulation of a micro-mechanically based dam-age model for soft collagenous tissues. The model is motivated by (i) a sliding filament model proposed in the literature [1] and (ii) by experimental observations from electron microscopy (EM) images of human abdominal aorta specimens, see [2]. Specifically, we derive a continuum damage model that takes into account statistically distributed pro- teoglycan (PG) bridges. The damage model is embedded into the constitutive framework proposed by Balzani et al. [3] and adjusted to cyclic uniaxial tension tests of a hu- man carotid artery. Furthermore, the resulting damage distribution of the model after a circumferential overstretch of a simplified
arterial section is analyzed in a finite element calculation
Non-Markovian Quantum State Diffusion for Temperature-Dependent Linear Spectra of Light Harvesting Aggregates
Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an
efficient method to calculate excitonic properties of aggregates composed of
organic chromophores, taking into account the coupling of electronic
transitions to vibrational modes of the chromophores. NMQSD is an open quantum
system approach that incorporates environmental degrees of freedom (the
vibrations in our case) in a stochastic way. We show in this paper that for
linear optical spectra (absorption, circular dichroism) no stochastics is
needed, even for finite temperatures. Thus, the spectra can be obtained by
propagating a single trajectory. To this end we map a finite temperature
environment to the zero temperature case using the so-called thermofield
method. The resulting equations can then be solved efficiently by standard
integrators.Comment: 14 pages, 4 figure
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