27,356 research outputs found
Compensating linkage for main rotor control
A compensating linkage for the rotor control system on rotary wing aircraft is described. The main rotor and transmission are isolated from the airframe structure by clastic suspension. The compensating linkage prevents unwanted signal inputs to the rotor control system caused by relative motion of the airframe structure and the main rotor and transmission
Airframe-integrated propulsion system for hypersonic cruise vehicles
Research on a new, hydrogen burning, airbreathing engine concept which offers good potential for efficient hypersonic cruise vehicles is considered. Features of the engine which lead to good performance include; extensive engine-airframe integration, fixed geometry, low cooling, and the control of heat release in the supersonic combustor by mixed-modes of fuel injection from the combustor entrance. The engine concept is described along with results from inlet tests, direct-connect combustor tests, and tests of two subscale boiler-plate research engines presently underway at conditions which simulate flight at Mach 4 and 7
A stacking method to study the gamma-ray emission of source samples based on the co-adding of Fermi LAT count maps
We present a stacking method that makes use of co-added maps of gamma-ray
counts produced from data taken with the Fermi Large Area Telescope. Sources
with low integrated gamma-ray fluxes that are not detected individually may
become detectable when their corresponding count maps are added. The combined
data set is analyzed with a maximum likelihood method taking into account the
contribution from point-like and diffuse background sources. For both simulated
and real data, detection significance and integrated gamma-ray flux are
investigated for different numbers of stacked sources using the public Fermi
Science Tools for analysis and data preparation. The co-adding is done such
that potential source signals add constructively, in contrast to the signals
from background sources, which allows the stacked data to be described with
simply structured models. We show, for different scenarios, that the stacking
method can be used to increase the cumulative significance of a sample of
sources and to characterize the corresponding gamma-ray emission. The method
can, for instance, help to search for gamma-ray emission from galaxy clusters.Comment: accepted for publication in Astronomy & Astrophysics, 10 pages, 12
figure
Ultrafast Insulator-Metal Phase Transition in VO2 Studied by Multiterahertz Spectroscopy
The ultrafast photoinduced insulator-metal transition in VO2 is studied at
different temperatures and excitation fluences using multi-THz probe pulses.
The spectrally resolved mid-infrared response allows us to trace separately the
dynamics of lattice and electronic degrees of freedom with a time resolution of
40 fs. The critical fluence of the optical pump pulse which drives the system
into a long-lived metallic state is found to increase with decreasing
temperature. Under all measurement conditions we observe a modulation of the
eigenfrequencies of the optical phonon modes induced by their anharmonic
coupling to the coherent wave packet motion of V-V dimers at 6.1 THz.
Furthermore, we find a weak quadratic coupling of the electronic response to
the coherent dimer oscillation resulting in a modulation of the electronic
conductivity at twice the frequency of the wave packet motion. The findings are
discussed in the framework of a qualitative model based on an approximation of
local photoexcitation of the vanadium dimers from the insulating state.Comment: 10 pages, 8 figures submitted to Physical Review
Experimentally Feasible Security Check for n-qubit Quantum Secret Sharing
In this article we present a general security strategy for quantum secret
sharing (QSS) protocols based on the HBB scheme presented by Hillery, Bu\v{z}ek
and Berthiaume [Phys. Rev A \textbf{59}, 1829 (1999)]. We focus on a
generalization of the HBB protocol to communication parties thus including
-partite GHZ states. We show that the multipartite version of the HBB scheme
is insecure in certain settings and impractical when going to large . To
provide security for such QSS schemes in general we use the framework presented
by some of the authors [M. Huber, F. Minert, A. Gabriel, B. C. Hiesmayr, Phys.
Rev. Lett. \textbf{104}, 210501 (2010)] to detect certain genuine partite
entanglement between the communication parties. In particular, we present a
simple inequality which tests the security.Comment: 5 pages, submitted to Phys. Rev.
Electrostatic Steering Accelerates C3d:CR2 Association.
Electrostatic effects are ubiquitous in protein interactions and are found to be pervasive in the complement system as well. The interaction between complement fragment C3d and complement receptor 2 (CR2) has evolved to become a link between innate and adaptive immunity. Electrostatic interactions have been suggested to be the driving factor for the association of the C3d:CR2 complex. In this study, we investigate the effects of ionic strength and mutagenesis on the association of C3d:CR2 through Brownian dynamics simulations. We demonstrate that the formation of the C3d:CR2 complex is ionic strength-dependent, suggesting the presence of long-range electrostatic steering that accelerates the complex formation. Electrostatic steering occurs through the interaction of an acidic surface patch in C3d and the positively charged CR2 and is supported by the effects of mutations within the acidic patch of C3d that slow or diminish association. Our data are in agreement with previous experimental mutagenesis and binding studies and computational studies. Although the C3d acidic patch may be locally destabilizing because of unfavorable Coulombic interactions of like charges, it contributes to the acceleration of association. Therefore, acceleration of function through electrostatic steering takes precedence to stability. The site of interaction between C3d and CR2 has been the target for delivery of CR2-bound nanoparticle, antibody, and small molecule biomarkers, as well as potential therapeutics. A detailed knowledge of the physicochemical basis of C3d:CR2 association may be necessary to accelerate biomarker and drug discovery efforts
Multi-component symmetry-projected approach for molecular ground state correlations
The symmetry-projected Hartree--Fock ansatz for the electronic structure
problem can efficiently account for static correlation in molecules, yet it is
often unable to describe dynamic correlation in a balanced manner. Here, we
consider a multi-component, systematically-improvable approach, that accounts
for all ground state correlations. Our approach is based on linear combinations
of symmetry-projected configurations built out of a set of non-orthogonal,
variationally optimized determinants. The resulting wavefunction preserves the
symmetries of the original Hamiltonian even though it is written as a
superposition of deformed (broken-symmetry) determinants. We show how short
expansions of this kind can provide a very accurate description of the
electronic structure of simple chemical systems such as the nitrogen and the
water molecules, along the entire dissociation profile. In addition, we apply
this multi-component symmetry-projected approach to provide an accurate
interconversion profile among the peroxo and bis(-oxo) forms of
[CuO], comparable to other state-of-the-art quantum chemical
methods
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