2,134 research outputs found
The drive system of the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope
The MAGIC telescope is an imaging atmospheric Cherenkov telescope, designed
to observe very high energy gamma-rays while achieving a low energy threshold.
One of the key science goals is fast follow-up of the enigmatic and short lived
gamma-ray bursts. The drive system for the telescope has to meet two basic
demands: (1) During normal observations, the 72-ton telescope has to be
positioned accurately, and has to track a given sky position with high
precision at a typical rotational speed in the order of one revolution per day.
(2) For successfully observing GRB prompt emission and afterglows, it has to be
powerful enough to position to an arbitrary point on the sky within a few ten
seconds and commence normal tracking immediately thereafter. To meet these
requirements, the implementation and realization of the drive system relies
strongly on standard industry components to ensure robustness and reliability.
In this paper, we describe the mechanical setup, the drive control and the
calibration of the pointing, as well as present measurements of the accuracy of
the system. We show that the drive system is mechanically able to operate the
motors with an accuracy even better than the feedback values from the axes. In
the context of future projects, envisaging telescope arrays comprising about
100 individual instruments, the robustness and scalability of the concept is
emphasized.Comment: 15 pages, 12 (10) figures, submitted to Astroparticle Physics, a high
resolution version of the paper (particularly fig. 1) is available at
http://publications.mppmu.mpg.de/2008/MPP-2008-101/FullText.pd
Entangling strings of neutral atoms in 1D atomic pipeline structures
We study a string of neutral atoms with nearest neighbor interaction in a 1D
beam splitter configuration, where the longitudinal motion is controlled by a
moving optical lattice potential. The dynamics of the atoms crossing the beam
splitter maps to a 1D spin model with controllable time dependent parameters,
which allows the creation of maximally entangled states of atoms by crossing a
quantum phase transition. Furthermore, we show that this system realizes
protected quantum memory, and we discuss the implementation of one- and
two-qubit gates in this setup.Comment: 4 pages, REVTEX, revised version: improvements in introduction and
figure
Entangled states of trapped ions allow measuring the magnetic field gradient of a single atomic spin
Using trapped ions in an entangled state we propose detecting a magnetic
dipole of a single atom at distance of a few m. This requires a
measurement of the magnetic field gradient at a level of about 10
Tesla/m. We discuss applications e.g. in determining a wide variation of
ionic magnetic moments, for investigating the magnetic substructure of ions
with a level structure not accessible for optical cooling and detection,and for
studying exotic or rare ions, and molecular ions. The scheme may also be used
for measureing spin imbalances of neutral atoms or atomic ensembles trapped by
optical dipole forces. As the proposed method relies on techniques well
established in ion trap quantum information processing it is within reach of
current technology.Comment: 4 pages, 2 fi
Quantum computations with atoms in optical lattices: marker qubits and molecular interactions
We develop a scheme for quantum computation with neutral atoms, based on the
concept of "marker" atoms, i.e., auxiliary atoms that can be efficiently
transported in state-independent periodic external traps to operate quantum
gates between physically distant qubits. This allows for relaxing a number of
experimental constraints for quantum computation with neutral atoms in
microscopic potential, including single-atom laser addressability. We discuss
the advantages of this approach in a concrete physical scenario involving
molecular interactions.Comment: 15 pages, 14 figure
A single trapped atom in front of an oscillating mirror
We investigate the Wigner-Weisskopf decay of a two level atom in front of an
oscillating mirror. This work builds on and extends previous theoretical and
experimental studies of the effects of a static mirror on spontaneous decay and
resonance fluorescence. The spontaneously emitted field is inherently
non-stationary due to the time-dependent boundary conditions and in order to
study its spectral distribution we employ the operational definition of the
spectrum of non-stationary light due to the seminal work by Eberly and
Wodkiewicz. We find a rich dependence of this spectrum as well as of the
effective decay rates and level shifts on the mirror-atom distance and on the
amplitude and frequency of oscillations of the mirror. The results presented
here provide the basis for future studies of more complex setups, where the
motion of the atom and/or the mirror are included as quantum degrees of
freedom.Comment: 10 pages, 12 figures, contribution to the special issue in Optics
Communications devoted to Krzysztof Wodkiewicz's memor
Genomic and Phenotypic Characterization of Clostridium botulinum Isolates from an Infant Botulism Case Suggests Adaptation Signatures to the Gut
In early life, the immature human gut microbiota is prone to colonization by pathogens that are usually outcompeted by mature microbiota in the adult gut. Colonization and neurotoxin production by a vegetative Clostridium botulinum culture in the gut of an infant can lead to flaccid paralysis, resulting in a clinical outcome known as infant botulism, a potentially life-threatening condition. Beside host factors, little is known of the ecology, colonization, and adaptation of C. botulinum to the gut environment. In our previous report, an infant with intestinal botulism was shown to be colonized by neurotoxigenic C. botulinum culture for 7 months. In an effort to gain ecological and evolutionary insights into this unusually long gut colonization by C. botulinum, we analyzed and compared the genomes of C. botulinum isolates recovered from the infant feces during the course of intoxication and isolates from the infant household dust. A number of observed mutations and genomic alterations pinpointed at phenotypic traits that may have promoted colonization and adaptation to the gut environment and to the host. These traits include motility, quorum-sensing, sporulation, and carbohydrate metabolism. We provide novel perspectives and suggest a tentative model of the pathogenesis of C. botulinum in infant botulism. IMPORTANCE While the clinical aspects of infant botulism and the mode of action of BoNT have been thoroughly investigated, little is known on the pathogenesis and adaptive mechanisms of C. botulinum in the gut. Here, we provide for the first time a comprehensive view on the genomic dynamics and plasticity of C. botulinum over time in a case of infant botulism. The genomic and phenotypic analysis of C. botulinum isolates collected during the disease course offers an unprecedented view of C. botulinum ecology, evolution, and pathogenesis and may be instrumental in developing novel strategies for prevention and treatment of toxicoinfectious botulism. While the clinical aspects of infant botulism and the mode of action of BoNT have been thoroughly investigated, little is known on the pathogenesis and adaptive mechanisms of C. botulinum in the gut. Here, we provide for the first time a comprehensive view on the genomic dynamics and plasticity of C. botulinum over time in a case of infant botulism.Peer reviewe
Dynamically stabilized decoherence-free states in non-Markovian open fermionic systems
Decoherence-free subspaces (DFSs) provide a strategy for protecting the
dynamics of an open system from decoherence induced by the system-environment
interaction. So far, DFSs have been primarily studied in the framework of
Markovian master equations. In this work, we study decoherence-free (DF) states
in the general setting of a non-Markovian fermionic environment. We identify
the DF states by diagonalizing the non-unitary evolution operator for a
two-level fermionic system attached to an electron reservoir. By solving the
exact master equation, we show that DF states can be stabilized dynamically.Comment: 11 pages, 3 figures. Any comments are welcom
Construction and validation of safe Clostridium botulinum Group II surrogate strain producing inactive botulinum neurotoxin type E toxoid
Botulinum neurotoxins (BoNTs), produced by the spore-forming bacterium Clostridium botulinum, cause botulism, a rare but fatal illness affecting humans and animals. Despite causing a life-threatening disease, BoNT is a multipurpose therapeutic. Nevertheless, as the most potent natural toxin, BoNT is classified as a Select Agent in the US, placing C. botulinum research under stringent governmental regulations. The extreme toxicity of BoNT, its impact on public safety, and its diverse therapeutic applications urge to devise safe solutions to expand C. botulinum research. Accordingly, we exploited CRISPR/Cas9-mediated genome editing to introduce inactivating point mutations into chromosomal bont/e gene of C. botulinum Beluga E. The resulting Beluga Ei strain displays unchanged physiology and produces inactive BoNT (BoNT/Ei) recognized in serological assays, but lacking biological activity detectable ex- and in vivo. Neither native single-chain, nor trypsinized di-chain form of BoNT/Ei show in vivo toxicity, even if isolated from Beluga Ei sub-cultured for 25 generations. Beluga Ei strain constitutes a safe alternative for the BoNT research necessary for public health risk management, the development of food preservation strategies, understanding toxinogenesis, and for structural BoNT studies. The example of Beluga Ei generation serves as template for future development of C. botulinum producing different inactive BoNT serotypes.Peer reviewe
- …