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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 103-108 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article reports a novel and simple cavity spectrometer for process monitoring of ethylene oxide sterilization, in which the source frequency, cavity resonant frequency, and gas absorption center frequency are asynchronous with respect to each other, thus, enabling sophisticated signal enhancement techniques to be employed without the need to engage the Stark effect. The operation of the device is such that the source frequency sweeps across a given range (F1 to F2) which contains one of the absorption peaks of the analyte gas (gases) of interest while the cavity resonant frequency Fr is oscillated within the profile of the absorption peak. Signal enhancement is achieved by adding a relatively small magnitude/high-frequency "dither'' signal to the source frequency sweep pattern. The salient information of the gas absorption due to the oscillation of the resonant frequency of the cavity is carried by the "dither'' signal and amplified and extracted by a series of tuned amplifiers and demodulators. Although the device is still at the initial design stage, a working prototype has been constructed in order to test the feasibility of the novel asynchronous modulation technique. This was achieved by successfully demonstrating that the device operates in an expected manner to within a standard error of 8.3%. It is believed that this error largely results from mechanical components. The significance of this error is greatly reduced when the spectrometer is operated in a large signal scanning mode as is the case when we apply the "power saturation'' technique to measure the concentration of ethylene oxide in the resonant cavity. This measurement showed that there is a good linear correlation between the output signal and the concentration of ethylene oxide gas (to within a standard error of 4%).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2343-2353 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The alignment between vorticity and eigenvectors of the strain-rate tensor in numerical solutions of Navier–Stokes turbulence is studied. Solutions for isotropic flow and homogeneous shear flow from pseudospectral calculations using 1283 grid points have been examined. The Taylor Reynolds number is 83 or greater. In both flows there is an increased probability for the vorticity to point in the intermediate strain direction and at three-fourths of the sample points this strain is positive (extensive). This propensity for vorticity alignment with a positive intermediate strain is a consequence of angular momentum conservation, as shown by a restricted Euler model of the coupling between strain and vorticity. Probability distributions for intermediate strain, conditioned on total strain, change from a symmetric triangular form at small strain to an asymmetric one for large strain. The most probable value of the asymmetric distribution gives strains in the ratios of 3:1: −4. The evolution of the distribution from a symmetric to an asymmetric form as the strain magnitude increases is essentially the same in both flows, indicating a generic structure of intense turbulence. The alignment between the gradient of a passive scalar and eigenvectors of the strain-rate tensor for Prandtl numbers of 0.1, 0.2, 0.5, and 1.0 has also been studied. There is an increased probability for the scalar gradient to align in the most compressive strain direction, and the average gradient is larger when it is pointing in that direction. Estimates for the scalar dissipation from the turbulent kinetic energy, its dissipation, and the root-mean-square scalar value are in reasonable agreement with calculated scalar dissipation if no explicit Prandtl number dependence is used in the estimate. Statistical analysis of scalar dissipation conditioned on energy dissipation yields a power-law relation between conditioned mean values. Both simulated flows are found to obey the qualitative predictions of the Gurvich–Yaglom (lognormal) intermittency model. Energy and scalar intermittency exponents are estimated and compared to measured values.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1978-01-01
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 1973-01-01
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2019-08-26
    Description: Networked social media provide governmental organizations, such as the National Weather Service (NWS), the opportunity to communicate directly with stakeholders over long periods of time as a form of online engagement. Typologies of engagement include aspects of message content that provide information, contribute to community building, and inspire action and aspects of message microstructural features that facilitate interaction and dialogue, such as directed messages, hashtags, and URLs. Currently, little is known regarding the effect of message strategies on behavioral outcomes, and whether those effects vary under different weather conditions. In this paper we examine how message practices used on Twitter by the NWS are related to message engagement under routine and nonroutine weather conditions. Our analysis employs a census of tweets sent by 12 NWS Weather Forecast Offices in spring 2016 and uses a combination of manual and automated coding to identify engagement content and microstructure features present in each message. We identify factors that increase and decrease message retransmission (retweets) within this corpus under varying threat conditions, using a mixed-effects negative binomial regression model. We find that inclusion of actionable message content, information about historical weather facts, attached visual imagery (such as a map or infograph), and named event hashtags increases message passing during both threat and nonthreat periods. In contrast, messages that include forecast and nowcast content and messages that are sent in reply to other users have a lower passing rate. Findings suggest that common message features do alter message passing, potentially informing message design practices aimed at increasing the reach of messages sent under threat conditions.
    Print ISSN: 1948-8327
    Electronic ISSN: 1948-8335
    Topics: Geosciences , Physics
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