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A micro-electro-mechanical-system-based thermal shear-stress sensor with self-frequency compensation
By applying the micro-electro-mechanical-system (MEMS) fabrication technology, we developed a micro-thermal sensor to measure surface shear stress. The heat transfer from a polysilicon heater depends on the normal velocity gradient and thus provides the surface shear stress. However, the sensitivity of the shear-stress measurements in air is less than desirable due to the low heat capacity of air. A unique feature of this micro-sensor is that the heating element, a film 1 µm thick, is separated from the substrate by a vacuum cavity 2 µm thick. The vacuum cavity prevents the conduction of heat to the substrate and therefore improves the sensitivity by an order of magnitude. Owing to the low thermal inertia of the miniature sensing element, this shear-stress micro-sensor can provide instantaneous measurements of small-scale turbulence. Furthermore, MEMS technology allows us make multiple sensors on a single chip so that we can perform distributed measurements. In this study, we use multiple polysilicon sensor elements to improve the dynamic performance of the sensor itself. It is demonstrated that the frequency-response range of a constant-current sensor can be extended from the order of 100 Hz to 100 kHz
Micro Balloon Actuators for Aerodynamic Control
A robust, large-force, large-deflection micro balloon actuator for aerodynamic (manoeuvring) control of transonic aircraft has been developed. Using a novel process, high yield linear arrays of silicone balloons on a robust silicon substrate have been fabricated that can deflect vertically in excess of one mm. Balloon actuators have been tested under cyclic conditions to assess reliability. The actuators have been characterized in a wind tunnel to assess their suitability as aerodynamic control surfaces and flight-tested on a jet fighter to assess their resistance to varied temperatures and pressures at high velocity
Aperture excited dielectric antennas
The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading
Multi-scales Approximations of Thin Flows for Curved Topography
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive
Electromagnetic modes of Maxwell fisheye lens
We provide an analysis of the radial structure of TE and TM modes of the
Maxwell fisheye lens, by means of Maxwell equations as applied to the fisheye
case. Choosing a lens of size R = 1 cm, we plot some of the modes in the
infrared range.Comment: 2+6 pages in Latex, 3 figures to be found in the published referenc
Dynamical coupled-channel model of kaon-hyperon interactions
The pi N --> KY and KY --> KY reactions are studied using a dynamical
coupled-channel model of meson-baryon interactions at energies where the baryon
resonances are strongly excited. The channels included are: pi N, K \Lambda,
and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710),
P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910),
P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660),
D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY
transition potentials are derived from effective Lagrangians using a unitary
transformation method. The dynamical coupled-channel equations are simplified
by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N
partial-wave amplitudes and a phenomenological off-shell function. Two models
have been constructed. Model A is built by fixing all coupling constants and
resonance parameters using SU(3) symmetry, the Particle Data Group values, and
results from a constituent quark model. Model B is obtained by allowing most of
the parameters to vary around the values of model A in fitting the data. Good
fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been
achieved. The investigated kinematics region in the center-of-mass frame goes
from threshold to 2.5 GeV. The constructed models can be imbedded into
associated dynamical coupled-channel studies of kaon photo- and
electro-production reactions.Comment: 35 pages, 11 Figure
A two-state model for helicase translocation and unwinding of nucleic acids
Helicases are molecular motors that unwind double-stranded nucleic acids
(dsNA), such as DNA and RNA). Typically a helicase translocates along one of
the NA single strands while unwinding and uses adenosine triphosphate (ATP)
hydrolysis as an energy source. Here we model of a helicase motor that can
switch between two states, which could represent two different points in the
ATP hydrolysis cycle. Our model is an extension of the earlier
Betterton-J\"ulicher model of helicases to incorporate switching between two
states. The main predictions of the model are the speed of unwinding of the
dsNA and fluctuations around the average unwinding velocity. Motivated by a
recent claim that the NS3 helicase of Hepatitis C virus follows a flashing
ratchet mechanism, we have compared the experimental results for the NS3
helicase with a special limit of our model which corresponds to the flashing
ratchet scenario. Our model accounts for one key feature of the experimental
data on NS3 helicase. However, contradictory observations in experiments
carried out under different conditions limit the ability to compare the model
to experiments.Comment: minor modification
Mgb2 Nonlinear Properties Investigated under Localized High RF Magnetic Field Excitation
In order to increase the accelerating gradient of Superconducting Radio
Frequency (SRF) cavities, Magnesium Diboride (MgB2) opens up hope because of
its high transition temperature and potential for low surface resistance in the
high RF field regime. However, due to the presence of the small superconducting
gap in the {\pi} band, the nonlinear response of MgB2 is potentially quite
large compared to a single gap s-wave superconductor (SC) such as Nb.
Understanding the mechanisms of nonlinearity coming from the two-band structure
of MgB2, as well as extrinsic sources, is an urgent requirement. A localized
and strong RF magnetic field, created by a magnetic write head, is integrated
into our nonlinear-Meissner-effect scanning microwave microscope [1]. MgB2
films with thickness 50 nm, fabricated by a hybrid physical-chemical vapor
deposition technique on dielectric substrates, are measured at a fixed location
and show a strongly temperature-dependent third harmonic response. We propose
that at least two mechanisms are responsible for this nonlinear response, one
of which involves vortex nucleation and penetration into the film. [1] T. M.
Tai, X. X. Xi, C. G. Zhuang, D. I. Mircea, S. M. Anlage, "Nonlinear Near-Field
Microwave Microscope for RF Defect Localization in Superconductors", IEEE
Trans. Appl. Supercond. 21, 2615 (2011).Comment: 6 pages, 6 figure
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