559 research outputs found
A calibration technique for a hot-wire-probe vector anemometer
Calibration tests using hot wires were conducted using a newly developed test rig that greatly reduced the data acquisition time. A comparison of measured and computed velocity vector magnitude and direction indicates the necessity of complete probe calibration to determine flow interference and/or operating limitation regions. Calibration results indicate that flow rates with 3 percent accuracy and flow angles with 5 deg accuracy are attainable
Characterization of particles in the Langley 0.3 meter transonic cryogenic tunnel using hot wire anemometry
Hot wire anemometry was used to identify the nature of particles reportedly observed during free stream velocity measurements in the Langley 0.3-meter transonic cryogenic tunnel using a Laser Doppler Velocimeter. Since the heat-transfer process from the hot wire depends on the thermal conductivity and sticking capability of the particles, it was anticipated that the hot wire anemometer response would be affected differently upon impaction by liquid droplets and solid aerosols in the test gas stream. Based on the measured time response of the hot-wire anemometer in the cryogenic tunnel operated in the 0.3-0.8 Mach number range, it is concluded that the particles impacting the hot wire are liquid in nature rather than solid aerosols. It is further surmised that the liquid aerosols are unevaporated liquid nitrogen droplets used for cooling the tunnel test gas
Phase lag in epidemics on a network of cities
We study the synchronisation and phase-lag of fluctuations in the number of
infected individuals in a network of cities between which individuals commute.
The frequency and amplitude of these oscillations is known to be very well
captured by the van Kampen system-size expansion, and we use this approximation
to compute the complex coherence function that describes their correlation. We
find that, if the infection rate differs from city to city and the coupling
between them is not too strong, these oscillations are synchronised with a well
defined phase lag between cities. The analytic description of the effect is
shown to be in good agreement with the results of stochastic simulations for
realistic population sizes.Comment: 10 pages, 6 figure
Components of multifractality in the Central England Temperature anomaly series
We study the multifractal nature of the Central England Temperature (CET)
anomaly, a time series that spans more than 200 years. The series is analyzed
as a complete data set and considering a sliding window of 11 years. In both
cases, we quantify the broadness of the multifractal spectrum as well as its
components defined by the deviations from the Gaussian distribution and the
influence of the dependence between measurements. The results show that the
chief contribution to the multifractal structure comes from the dynamical
dependencies, mainly the weak ones, followed by a residual contribution of the
deviations from Gaussianity. However, using the sliding window, we verify that
the spikes in the non-Gaussian contribution occur at very close dates
associated with climate changes determined in previous works by component
analysis methods. Moreover, the strong non-Gaussian contribution found in the
multifractal measures from the 1960s onwards is in agreement with global
results very recently proposed in the literature.Comment: 21 pages, 10 figure
Suspension plasma spraying of nanostructured WC-12Co coatings
Nanostructured WC-12% Co coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier used in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a fine surface finish.Apolyethylene-imine (PEI) dispersant was used to stabilize the colloidal suspension in an ethanol carrier. In-flight particle states were measured for a number of operating conditions of varying plasma gas flow rates, feed rates, and standoff distances and were related to the resulting microstructure, phase composition (EDS, SEM, XRD), and Vickers hardness. High in-flight particle velocities (>800 m/s) were generated, leading to dense coatings. It was observed that the coating quality was generally compromised by the high temperature and reactivity of the small particles. To compensate for this shortcoming, the suspension feed rate was adjusted, thereby varying the thermal load on the plasma. Results showed that a slightly larger agglomerate size, in conjunction with low particle jet temperatures, could somewhat limit the decomposition of WC into brittle W\u2082C/W\u2083C and amorphous cobalt containing binder phases.Peer reviewed: YesNRC publication: Ye
Semiclassical mechanics of a non-integrable spin cluster
We study detailed classical-quantum correspondence for a cluster system of
three spins with single-axis anisotropic exchange coupling. With autoregressive
spectral estimation, we find oscillating terms in the quantum density of states
caused by classical periodic orbits: in the slowly varying part of the density
of states we see signs of nontrivial topology changes happening to the energy
surface as the energy is varied. Also, we can explain the hierarchy of quantum
energy levels near the ferromagnetic and antiferromagnetic states with EKB
quantization to explain large structures and tunneling to explain small
structures.Comment: 9 pages. For related works see
"http://www.msc.cornell.edu/~clh/clh.html
Extension of SPIS to simulate dust electrostatic charging, transport and contamination of lunar probes
A modification of the Spacecraft Plasma Interaction Software has been undertaken under ESA contract 4000107327/12/NL/AK (SPIS-DUST). The primary goal is to provide mission designers with an engineering tool capable of predicting charged dust behavior in a given plasma environment involving a spacecraft / exploration unit in contact with complex topological features at various locations of the Moon’s surface. The tool also aims at facilitating dust contamination diagnostics for sensitive surfaces such as sensors optics, solar panels, thermal interfaces, etc. In this paper, the new user interface and the new numerical solvers developed in the frame of this project is presented. The pre-processing includes the building of a 3D lunar surface from a topology description (i.e. a point list), an interface to position the spacecraft and a merging interface for the spacecraft elements in contact with the lunar surface. Concerning the physical models, the new solvers have been developed in order to model the physics of the ejection of the dust from the soils, the dusts charging and transport in volume and the dust interaction and contamination of the spacecraft. The post-processing includes the standard outputs of SPIS for the electrostatic computation and the plasma plus dedicated instruments for the diagnosis of the dusts. A set of verification test cases are presented in order to demonstrate the new capabilities of this version of SPIS in realistic conditions
Thermo Mechanical Behavior of Nanostructured Plasma Sprayed Zirconia Coatings
Peer reviewed: NoNRC publication: Ye
Mapping language function with task-based vs. resting-state functional MRI
BACKGROUND: Use of functional MRI (fMRI) in pre-surgical planning is a non-invasive method for pre-operative functional mapping for patients with brain tumors, especially tumors located near eloquent cortex. Currently, this practice predominantly involves task-based fMRI (T-fMRI). Resting state fMRI (RS-fMRI) offers an alternative with several methodological advantages. Here, we compare group-level analyses of RS-fMRI vs. T-fMRI as methods for language localization.
PURPOSE: To contrast RS-fMRI vs. T-fMRI as techniques for localization of language function.
METHODS: We analyzed data obtained in 35 patients who had both T-fMRI and RS-fMRI scans during the course of pre-surgical evaluation. The RS-fMRI data were analyzed using a previously trained resting-state network classifier. The T-fMRI data were analyzed using conventional techniques. Group-level results obtained by both methods were evaluated in terms of two outcome measures: (1) inter-subject variability of response magnitude and (2) sensitivity/specificity analysis of response topography, taking as ground truth previously reported maps of the language system based on intraoperative cortical mapping as well as meta-analytic maps of language task fMRI responses.
RESULTS: Both fMRI methods localized major components of the language system (areas of Broca and Wernicke) although not with equal inter-subject consistency. Word-stem completion T-fMRI strongly activated Broca\u27s area but also several task-general areas not specific to language. RS-fMRI provided a more specific representation of the language system.
CONCLUSION: We demonstrate several advantages of classifier-based mapping of language representation in the brain. Language T-fMRI activated task-general (i.e., not language-specific) functional systems in addition to areas of Broca and Wernicke. In contrast, classifier-based analysis of RS-fMRI data generated maps confined to language-specific regions of the brain
- …