7,817 research outputs found
Gas turbine rotor/case structural response to rotating stall: Experimental documentation and analytical approach
The forcing functions and structural responses characterizing gas turbine rotor/case system vibration due to rotating stall in an axial flow compressor are described. Two data sets with fundamentally different response characteristics are presented; one is supersynchronous and the other subsynchronous. Conventional beam element rotor dynamics analysis is shown to be severely limited in its ability to predict these responses. A new analytical approach, which significantly increases structural response predictive capability for these phenomena, is briefly discussed
Extending Continuum Models for Atom Probe Simulation
This work describes extensions to existing level-set algorithms developed for
application within the field of Atom Probe Tomography (APT). We present a new
simulation tool for the simulation of 3D tomographic volumes, using advanced
level set methods. By combining narrow-band, B-Tree and particle-tracing
approaches from level-set methods, we demonstrate a practical tool for
simulating shape changes to APT samples under applied electrostatic fields, in
three dimensions. This work builds upon our previous studies by allowing for
non-axially symmetric solutions, with minimal loss in computational speed,
whilst retaining numerical accuracy
Microkelvin thermometry with Bose-Einstein condensates of magnons and applications to studies of the AB interface in superfluid He
Coherent precession of trapped Bose-Einstein condensates of magnons is a
sensitive probe for magnetic relaxation processes in superfluid 3He-B down to
the lowest achievable temperatures. We use the dependence of the relaxation
rate on the density of thermal quasiparticles to implement thermometry in 3He-B
at temperatures below 300 K. Unlike popular vibrating wire or quartz
tuning fork based thermometers, magnon condensates allow for contactless
temperature measurement and make possible an independent in situ determination
of the residual zero-temperature relaxation provided by the radiation damping.
We use this magnon-condensate-based thermometry to study the thermal impedance
of the interface between A and B phases of superfluid 3He. The magnon
condensate is also a sensitive probe of the orbital order-parameter texture.
This has allowed us to observe for the first time the non-thermal signature of
the annihilation of two AB interfaces.Comment: 26 pages, 7 figures, manuscript prepared for EU Microkelvin
Collaboration Workshop 2013. Accepted for publication in Journal of Low
Temperature Physic
Estimation of Kalman filter model parameters from an ensemble of tests
A methodology for estimating initial mean and covariance parameters in a Kalman filter model from an ensemble of nonidentical tests is presented. In addition, the problem of estimating time constants and process noise levels is addressed. Practical problems such as developing and validating inertial instrument error models from laboratory test data or developing error models of individual phases of a test are generally considered
Reciprocal Inhibition of Adiponectin and Innate Lung Immune Responses to Chitin and Aspergillus fumigatus
Chitin is a structural biopolymer found in numerous organisms, including pathogenic fungi, and recognized as an immune-stimulating pathogen associated molecular pattern by pattern recognition molecules of the host immune system. However, programming and regulation of lung innate immunity to chitin inhalation in the context of inhalation of fungal pathogens such as Aspergillus fumigatus is complex and our understanding incomplete. Here we report that the systemic metabolism-regulating cytokine adiponectin is decreased in the lungs and serum of mice after chitin inhalation, with a concomitant decrease in surface expression of the adiponectin receptor AdipoR1 on lung leukocytes. Constitutive lung expression of acidic mammalian chitinase resulted in decreased inflammatory cytokine gene expression and neutrophil recruitment, but did not significantly affect lung adiponectin transcription. Exogenous recombinant adiponectin specifically dampened airway chitin-mediated eosinophil recruitment, while adiponectin deficiency resulted in increased airway eosinophils. The presence of adiponectin also resulted in decreased CCL11-mediated migration of bone marrow-derived eosinophils. In contrast to purified chitin, aspiration of viable conidia from the high chitin-expressing A. fumigatus isolate Af5517 resulted in increased neutrophil recruitment and inflammatory cytokine gene expression in adiponectin-deficient mice, while no significant changes were observed in response to the isolate Af293. Our results identify a novel role for the adiponectin pathway in inhibition of lung inflammatory responses to chitin and A. fumigatus inhalation
Picking battles: The impact of trust assumptions on the elaboration of security requirements
This position paper describes work on trust assumptions in the con-text of security requirements. We show how trust assumptions can affect the scope of the analysis, derivation of security requirements, and in some cases how functionality is realized. An example shows how trust assumptions are used by a requirements engineer to help define and limit the scope of analysis and to document the decisions made during the process
DF-Fit : A robust algorithm for detection of crystallographic information in Atom Probe Tomography data
We report on a new algorithm for detection of crystallographic information in
3D, as retained in Atom Probe Tomography (APT), with improved robustness and
signal detection performance. The algorithm is underpinned by 1D distribution
functions, as per existing algorithms, but eliminates an unnecessary parameter
as compared to current methods. By examining traditional distribution functions
in an automated fashion in real space, rather than using Fourier transform
approaches, we utilise an error metric based upon the expected value for a
spatially random distribution for detecting crystallography. We show cases
where the metric is able to successfully obtain orientation information, and
show that it can function with high levels of additive and displacive
background noise. We additionally compare this metric to Fourier transform
methods, showing fewer artefacts when examining simulated datasets. An
extension of the approach is used to aid the automatic detection of
high-quality data regions within an entire dataset, albeit with a large
increase in computational cost. This extension is demonstrated on acquired
Aluminium and Tungsten APT datasets, and shown to be able to discern regions of
the data which have relatively improved spatial data quality. Finally, this
program has been made available for use in other laboratories undertaking their
own analyses
Vacancy clustering and diffusion in silicon: Kinetic lattice Monte Carlo simulations
Diffusion and clustering of lattice vacancies in silicon as a function of
temperature, concentration, and interaction range are investigated by Kinetic
Lattice Monte Carlo simulations. It is found that higher temperatures lead to
larger clusters with shorter lifetimes on average, which grow by attracting
free vacancies, while clusters at lower temperatures grow by aggregation of
smaller clusters. Long interaction ranges produce enhanced diffusivity and
fewer clusters. Greater vacancy concentrations lead to more clusters, with
fewer free vacancies, but the size of the clusters is largely independent of
concentration. Vacancy diffusivity is shown to obey power law behavior over
time, and the exponent of this law is shown to increase with concentration, at
fixed temperature, and decrease with temperature, at fixed concentration.Comment: 14 pages, 12 figures. To appear in Physical Review
Nanoelectronic thermometers optimised for sub-10 millikelvin operation
We report the cooling of electrons in nanoelectronic Coulomb blockade
thermometers below 4 mK. Above 7 mK the devices are in good thermal contact
with the environment, well isolated from electrical noise, and not susceptible
to self-heating. This is attributed to an optimised design that incorporates
cooling fins with a high electron-phonon coupling and on-chip electronic
filters, combined with a low-noise electronic measurement setup. Below 7 mK the
electron temperature is seen to diverge from the ambient temperature. By
immersing a Coulomb Blockade Thermometer in the 3He/4He refrigerant of a
dilution refrigerator, we measure a lowest electron temperature of 3.7 mK.Comment: 11 pages, 4 figures. (Fixed fitted saturation T_e on p9
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