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Path instabilities of light particles rising in a liquid with background rotation
The present paper reports on experimental observations performed on 2–6 mm low-density polystyrene particles rising freely in a water-glycerol mixture for the liquid at rest as well as with slow background rotation (axisymmetric solid body rotation around the vertical axis). Particle trajectories were studied in the Reynolds-numbers range of 200<Re<800 at a fixed rotation rate of Ω=0.81/s. Both the trajectory measurements and the wake visualization indicate that there are differences in the wake structure of the particles as well as in the path instabilities compared to those in quiescent fluid. In the swirling flow, the two-threaded wake mode is dominant up to Reynolds numbers of about 500 with typical spiral-type trajectories until vortex shedding commences. In contrast, under quiescent flow conditions vortex shedding already occurs above Re=230, and the particles predominantly move in zig-zagging paths. Thus, the presence of background rotation is able to suppress vortex shedding and to delay the transition. For the co-rotating observer, the radius of the spiral-type path is comparable to that of the transversal motion under quiescent flow conditions. Therefore, the magnitude of lateral lift-forces is not greatly affected by the presence of the swirl
Effect of varying day-length on time of oviposition in domestic fowl
This bulletin reports on University of Missouri Agricultural Experiment Station research project 292, Poultry Photoperiodicity--P. [2].Digitized 2007 AES.Includes bibliographical references (pages 48-52)
Exposure Setup and Dosimetry for a Study on Effects of Mobile Communication Signals on Human Hematopoietic Stem Cells in vitro
In this paper we describe the design of an exposure setup used to
study possible non-thermal effects due to the exposure of human hematopoietic
stem cells to GSM, UMTS and LTE mobile communication signals. The experiments
are performed under fully blinded conditions in a TEM waveguide located
inside an incubator to achieve defined environmental conditions as required
for the living cells. Chamber slides containing the cells in culture medium
are placed on the septum of the waveguide. The environmental and exposure
parameters such as signal power, temperatures, relative humidity and CO2
content of the surrounding atmosphere are monitored permanently during the
exposure experiment. The power of the exposure signals required to achieve
specific absorption rates of 0.5, 1, 2 and 4 W kg−1 are
determined by numerical calculation of the field distribution inside the cell
culture medium at 900 MHz (GSM), 1950 MHz (UMTS) and 2535 MHz (LTE). The
dosimetry is verified both with scattering parameter measurements on the
waveguide with and without containers filled with cell culture medium and
with temperature measurements with non-metallic probes in separate heating
experiments
Metamaterial Polarization Converter Analysis: Limits of Performance
In this paper we analyze the theoretical limits of a metamaterial converter
that allows for linear-to- elliptical polarization transformation with any
desired ellipticity and ellipse orientation. We employ the transmission line
approach providing a needed level of the design generalization. Our analysis
reveals that the maximal conversion efficiency for transmission through a
single metamaterial layer is 50%, while the realistic re ection configuration
can give the conversion efficiency up to 90%. We show that a double layer
transmission converter and a single layer with a ground plane can have 100%
polarization conversion efficiency. We tested our conclusions numerically
reaching the designated limits of efficiency using a simple metamaterial
design. Our general analysis provides useful guidelines for the metamaterial
polarization converter design for virtually any frequency range of the
electromagnetic waves.Comment: 10 pages, 11 figures, 2 table
Terahertz time-domain spectroscopy and imaging of artificial RNA
This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsexpress.org/abstract.cfm?id=84667. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.We use terahertz time-domain spectroscopy (THz-TDS) to measure the far-infrared dielectric function of two artificial RNA single strands, composed of polyadenylic acid (poly-A) and polycytidylic acid (poly-C). We find a significant difference in the absorption between the two types of RNA strands, and we show that we can use this difference to record images of spot arrays of the RNA strands. Under controlled conditions it is possible to use the THz image to distinguish between the two RNA strands. We discuss the requirements to sample preparation imposed by the lack of sharp spectral features in the absorption spectra.Bernd Fischer, Matthias Hoffmann, Hanspeter Helm, Rafal Wilk, Frank Rutz, Thomas Kleine-Ostmann, Martin Koch, Peter Jepse
Highly-Sensitive Thin Film THz Detector Based on Edge Metal-Semiconductor-Metal Junction
Terahertz (THz) detectors have been extensively studied for various applications such as security, wireless communication, and medical imaging. In case of metal-insulator-metal (MIM) tunnel junction THz detector, a small junction area is desirable because the detector response time can be shortened by reducing it. An edge metal-semiconductor-metal (EMSM) junction has been developed with a small junction area controlled precisely by the thicknesses of metal and semiconductor films. The voltage response of the EMSM THz detector shows the clear dependence on the polarization angle of incident THz wave and the responsivity is found to be very high (similar to 2,169 V/W) at 0.4 THz without any antenna and signal amplifier. The EMSM junction structure can be a new and efficient way of fabricating the nonlinear device THz detector with high cut-off frequency relying on extremely small junction area
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