330 research outputs found
Fiber modulators and fiber amplifiers for LISA
We present the sideband phase characteristics of a fiber-coupled integrated electro-optical modulator (EOM) at a modulation frequency of 2 GHz for Fourier frequencies from 0.1 mHz to 1 Hz. The upper phase noise limit was almost an order of magnitude better than required for LISA. The EOM's phase dependencies on temperature and transmitted optical power were measured and found to be uncritical. Additionally we have investigated three optical amplifiers emitting 1 W. Their differential phase noise and optical pathlength noise as one contribution to differential phase noise were measured. The measured differential phase noise was within the requirement. The dependencies of differential phase noise on pump power were measured and requirements for the operation of the amplifier on the LISA satellite derived.DLR/50 OQ 0601DFG/EXC/QUES
Multiple Conclusion Rules in Logics with the Disjunction Property
We prove that for the intermediate logics with the disjunction property any
basis of admissible rules can be reduced to a basis of admissible m-rules
(multiple-conclusion rules), and every basis of admissible m-rules can be
reduced to a basis of admissible rules. These results can be generalized to a
broad class of logics including positive logic and its extensions, Johansson
logic, normal extensions of S4, n-transitive logics and intuitionistic modal
logics
Geometric representations for minimalist grammars
We reformulate minimalist grammars as partial functions on term algebras for
strings and trees. Using filler/role bindings and tensor product
representations, we construct homomorphisms for these data structures into
geometric vector spaces. We prove that the structure-building functions as well
as simple processors for minimalist languages can be realized by piecewise
linear operators in representation space. We also propose harmony, i.e. the
distance of an intermediate processing step from the final well-formed state in
representation space, as a measure of processing complexity. Finally, we
illustrate our findings by means of two particular arithmetic and fractal
representations.Comment: 43 pages, 4 figure
In situ uniaxial pressure cell for x-ray and neutron scattering experiments
We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes
Self-assembly of ordered wurtzite/rock salt heterostructuresâA new view on phase separation in MgxZn1âxO
The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1âxO heterostructures by planar phase separation is shown. These heterostructures form quasi ânaturalâ two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1âxO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900â°C and 1000â°C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1âxO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth
In situ uniaxial pressure cell for x-ray and neutron scattering experiments
We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes
Changing a semantics: opportunism or courage?
The generalized models for higher-order logics introduced by Leon Henkin, and
their multiple offspring over the years, have become a standard tool in many
areas of logic. Even so, discussion has persisted about their technical status,
and perhaps even their conceptual legitimacy. This paper gives a systematic
view of generalized model techniques, discusses what they mean in mathematical
and philosophical terms, and presents a few technical themes and results about
their role in algebraic representation, calibrating provability, lowering
complexity, understanding fixed-point logics, and achieving set-theoretic
absoluteness. We also show how thinking about Henkin's approach to semantics of
logical systems in this generality can yield new results, dispelling the
impression of adhocness. This paper is dedicated to Leon Henkin, a deep
logician who has changed the way we all work, while also being an always open,
modest, and encouraging colleague and friend.Comment: 27 pages. To appear in: The life and work of Leon Henkin: Essays on
his contributions (Studies in Universal Logic) eds: Manzano, M., Sain, I. and
Alonso, E., 201
Empfehlungen zur Erstellung von Stellungnahmen zur seismischen GefÀhrdung bei tiefengeothermischen Projekten
Detecting controlling nodes of boolean regulatory networks
Boolean models of regulatory networks are assumed to be tolerant to perturbations. That qualitatively implies that each function can only depend on a few nodes. Biologically motivated constraints further show that functions found in Boolean regulatory networks belong to certain classes of functions, for example, the unate functions. It turns out that these classes have specific properties in the Fourier domain. That motivates us to study the problem of detecting controlling nodes in classes of Boolean networks using spectral techniques. We consider networks with unbalanced functions and functions of an average sensitivity less than 23k, where k is the number of controlling variables for a function. Further, we consider the class of 1-low networks which include unate networks, linear threshold networks, and networks with nested canalyzing functions. We show that the application of spectral learning algorithms leads to both better time and sample complexity for the detection of controlling nodes compared with algorithms based on exhaustive search. For a particular algorithm, we state analytical upper bounds on the number of samples needed to find the controlling nodes of the Boolean functions. Further, improved algorithms for detecting controlling nodes in large-scale unate networks are given and numerically studied
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