293 research outputs found
A method to estimate weight and dimensions of aircraft gas turbine engines. Volume 1: Method of analysis
Weight and envelope dimensions of aircraft gas turbine engines are estimated within plus or minus 5% to 10% using a computer method based on correlations of component weight and design features of 29 data base engines. Rotating components are estimated by a preliminary design procedure where blade geometry, operating conditions, material properties, shaft speed, hub-tip ratio, etc., are the primary independent variables used. The development and justification of the method selected, the various methods of analysis, the use of the program, and a description of the input/output data are discussed
A method to estimate weight and dimensions of aircraft gas turbine engines. Volume 2: User's manual
For abstract, see N77-25171
The RTM harmonic correction revisited
In this paper, we derive improved expressions for the harmonic correction to gravity and, for the first time, expressions for the harmonic correction to potential and height anomaly. They need to be applied at stations buried inside the masses to transform internal values into harmonically downward continued values, which are then input to local quasi-geoid modelling using least-squares collocation or least-squares techniques in combination with the remove-compute-restore approach. Harmonic corrections to potential and height anomaly were assumed to be negligible so far resulting in yet unknown quasi-geoid model errors. The improved expressions for the harmonic correction to gravity, and the new expressions for the harmonic correction to potential and height anomaly are used to quantify the approximation errors of the commonly used harmonic correction to gravity and to quantify the magnitude of the harmonic correction to potential and height anomaly. This is done for two test areas with different topographic regimes. One comprises parts of Norway and the North Atlantic where the presence of deep, long, and narrow fjords suggest extreme values for the harmonic correction to potential and height anomaly and corresponding large errors of the commonly used approximation of the harmonic correction to gravity. The other one is located in the Auvergne test area with a moderate topography comprising both flat and hilly areas and therefore may be representative for many areas around the world. For both test areas, two RTM surfaces with different smoothness are computed simulating the use of a medium-resolution and an ultra-high-resolution reference gravity field, respectively. We show that the errors of the commonly used harmonic correction to gravity may be as large as the harmonic correction itself and attain peak values in areas of strong topographic variations of about 100 mGal. Moreover, we show that this correction may introduce long-wavelength biases in the computed quasi-geoid model. Furthermore, we show that the harmonic correction to height anomaly can attain values on the order of a decimetre at some points. Overall, however, the harmonic correction to height anomaly needs to be applied only in areas of strong topographic variations. In flat or hilly areas, it is mostly smaller than one centimetre. Finally, we show that the harmonic corrections increase with increasing smoothness of the RTM surface, which suggests to use a RTM surface with a spatial resolution comparable to the finest scales which can be resolved by the data rather than depending on the resolution of the global geopotential model used to reduce the data
A method to estimate weight and dimensions of aircraft gas turbine engines. Volume 3: Programmer's manual
For abstract, see N77-25171
Interplay Between Yu-Shiba-Rusinov States and Multiple Andreev Reflections
Motivated by recent scanning tunneling microscopy experiments on single
magnetic impurities on superconducting surfaces, we present here a
comprehensive theoretical study of the interplay between Yu-Shiba-Rusinov bound
states and (multiple) Andreev reflections. Our theory is based on a combination
of an Anderson model with broken spin degeneracy and nonequilibrium Green's
function techniques that allows us to describe the electronic transport through
a magnetic impurity coupled to superconducting leads for arbitrary junction
transparency. Using this combination we are able to elucidate the different
tunneling processes that give a significant contribution to the subgap
transport. In particular, we predict the occurrence of a large variety of
Andreev reflections mediated by Yu-Shiba-Rusinov bound states that clearly
differ from the standard Andreev processes in non-magnetic systems. Moreover,
we provide concrete guidelines on how to experimentally identify the subgap
features originating from these tunneling events. Overall, our work provides
new insight into the role of the spin degree of freedom in Andreev transport
physics.Comment: 15 pages, 10 figure
Earth’s gravity field modelling based on satellite accelerations derived from onboard GPS phase measurements
<p>GPS data collected by satellite gravity missions can be used for extracting the long-wavelength part of the Earth’s gravity field. We propose a new data processing method which makes use of the ‘average acceleration’ approach to gravity field modelling. In this method, satellite accelerations are directly derived from GPS carrier phase measurements with an epoch-differenced scheme. As a result, no ambiguity solutions are needed and the systematic errors that do not change much from epoch to epoch are largely eliminated. The GPS data collected by the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission are used to demonstrate the added value of the proposed method. An analysis of the residual accelerations shows that accelerations derived in this way are more precise, with noise being reduced by about 20 and 5% at the cross-track component and the other two components, respectively, as compared to those based on kinematic orbits. The accelerations obtained in this way allow the recovery of the gravity field to a slightly higher maximum degree compared to the solution based on kinematic orbits. Furthermore, the gravity field solution has an overall better performance. Errors in spherical harmonic coefficients are smaller, especially at low degrees. The cumulative geoid height error is reduced by about 15 and 5% up to degree 50 and 150, respectively. An analysis in the spatial domain shows that large errors along the geomagnetic equator, which are caused by a high electron density coupled with large short-term variations, are substantially reduced. Finally, the new method allows for a better observation of mass transport signals. In particular, sufficiently realistic signatures of regional mass anomalies in North America and south-west Africa are obtained.</p
Microwave spectroscopy reveals the quantum geometric tensor of topological Josephson matter
Quantization effects due to topological invariants such as Chern numbers have become very relevant in many systems, yet key quantities such as the quantum geometric tensor providing local information about quantum states remain experimentally difficult to access. Recently, it has been shown that multiterminal Josephson junctions constitute an ideal platform to synthesize topological systems in a controlled manner. We theoretically study properties of Andreev states in topological Josephson matter and demonstrate that the quantum geometric tensor of Andreev states can be extracted by synthetically polarized microwaves. The oscillator strength of the absorption rates provides direct evidence of topological quantum properties of the Andreev states.publishe
Tunneling processes between Yu-Shiba-Rusinov bound states
Very recent experiments have reported the tunneling between Yu-Shiba-Rusinov
(YSR) bound states at the atomic scale. These experiments have been realized
with the help of a scanning tunneling microscope where a superconducting tip is
functionalized with a magnetic impurity and is used to probe another magnetic
impurity deposited on a superconducting substrate. In this way it has become
possible to study for the first time the spin-dependent transport between
individual superconducting bound states. Motivated by these experiments, we
present here a comprehensive theoretical study of the tunneling processes
between YSR bound states in a system in which two magnetic impurities are
coupled to superconducting leads. Our theory is based on a combination of an
Anderson model with broken spin degeneracy to describe the impurities and
nonequilibrium Green's function techniques to compute the current-voltage
characteristics. This combination allows us to describe the spin-dependent
transport for an arbitrary strength of the tunnel coupling between the
impurities. We first focus on the tunnel regime and show that our theory
naturally explains the experimental observations of the appearance of current
peaks in the subgap region due to both the direct and thermal tunneling between
the YSR states in both impurities. Then, we study in detail the case of
junctions with increasing transparency, which has not been experimentally
explored yet, and predict the occurrence of a large variety of (multiple)
Andreev reflections mediated by YSR states that give rise to a very rich
structure in the subgap current. In particular, we predict the occurrence of
multiple Andreev reflections that involve YSR states in different impurities.
These processes have no analogue in single-impurity junctions and they are
manifested as current peaks with negative differential conductance for subgap
voltages.Comment: 16 pages, 9 figures. arXiv admin note: text overlap with
arXiv:2005.0649
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