33,551 research outputs found
Experimental investigation of the effects of polarization on the measured radiation efficiency of a dielectric resonator antenna
©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.The radiation efficiencies of two rectangular dielectric resonant antennas (DRAs) were investigated using the directivity/ gain (D/G) method and the Wheeler cap method. Both antennas are linearly polarized but have different linear polarization purities. Through comparison of their radiation efficiencies, itpsilas shown that the polarization purity strongly affects the D/G measurement of the DRAspsila radiation efficiency.Qinghua Lai, Georgios Almpanis, Christophe Fumeaux, Hansruedi Benedickter, and Rüdiger Vahldiec
Two-dimensional viscous flow computations of hypersonic scramjet nozzle flowfields at design and off-design conditions
The PARC2D code has been selected to analyze the flowfields of a representative hypersonic scramjet nozzle over a range of flight conditions from Mach 3 to 20. The flowfields, wall pressures, wall skin friction values, heat transfer values and overall nozzle performance are presented
Particle phenomenology on noncommutative spacetime
We introduce particle phenomenology on the noncommutative spacetime called
the Groenewold-Moyal plane. The length scale of spcetime noncommutativity is
constrained from the CPT violation measurements in system
and difference of . The system
provides an upper bound on the length scale of spacetime noncommutativity of
the order of , corresponding to a lower energy bound
of the order of . The difference of constrains the noncommutativity length scale to be of the order of
, corresponding to a lower energy bound of the order
of .
We also present the phenomenology of the electromagnetic interaction of
electrons and nucleons at the tree level in the noncommutative spacetime. We
show that the distributions of charge and magnetization of nucleons are
affected by spacetime noncommutativity. The analytic properties of
electromagnetic form factors are also changed and it may give rise to
interesting experimental signals.Comment: 10 pages, 3 figures. Published versio
Viscous three-dimensional analyses for nozzles for hypersonic propulsion
A Navier-Stokes computer code was validated using a number of two- and three-dimensional configurations for both laminar and turbulent flows. The validation data covers a range of freestream Mach numbers from 3 to 14, includes wall pressures, velocity profiles, and skin friction. Nozzle flow fields computed for a generic scramjet nozzle from Mach 3 to 20, wall pressures, wall skin friction values, heat transfer values, and overall performance are presented. In addition, three-dimensional solutions obtained for two asymmetric, single expansion ramp nozzles at a pressure ratio of 10 consists of the internal expansion region in the converging/diverging sections and the external supersonic exhaust in a quiescent ambient environment. The fundamental characteristics that were captured successfully include expansion fans; Mach wave reflections; mixing layers; and nonsymmetrical, multiple inviscid cell, supersonic exhausts. Comparison with experimental data for wall pressure distributions at the center planes shows good agreement
A compressible near-wall turbulence model for boundary layer calculations
A compressible near-wall two-equation model is derived by relaxing the assumption of dynamical field similarity between compressible and incompressible flows. This requires justifications for extending the incompressible models to compressible flows and the formulation of the turbulent kinetic energy equation in a form similar to its incompressible counterpart. As a result, the compressible dissipation function has to be split into a solenoidal part, which is not sensitive to changes of compressibility indicators, and a dilational part, which is directly affected by these changes. This approach isolates terms with explicit dependence on compressibility so that they can be modeled accordingly. An equation that governs the transport of the solenoidal dissipation rate with additional terms that are explicitly dependent on the compressibility effects is derived similarly. A model with an explicit dependence on the turbulent Mach number is proposed for the dilational dissipation rate. Thus formulated, all near-wall incompressible flow models could be expressed in terms of the solenoidal dissipation rate and straight-forwardly extended to compressible flows. Therefore, the incompressible equations are recovered correctly in the limit of constant density. The two-equation model and the assumption of constant turbulent Prandtl number are used to calculate compressible boundary layers on a flat plate with different wall thermal boundary conditions and free-stream Mach numbers. The calculated results, including the near-wall distributions of turbulence statistics and their limiting behavior, are in good agreement with measurements. In particular, the near-wall asymptotic properties are found to be consistent with incompressible behavior; thus suggesting that turbulent flows in the viscous sublayer are not much affected by compressibility effects
A near-wall two-equation model for compressible turbulent flows
A near-wall two-equation turbulence model of the K - epsilon type is developed for the description of high-speed compressible flows. The Favre-averaged equations of motion are solved in conjunction with modeled transport equations for the turbulent kinetic energy and solenoidal dissipation wherein a variable density extension of the asymptotically consistent near-wall model of So and co-workers is supplemented with new dilatational models. The resulting compressible two-equation model is tested in the supersonic flat plate boundary layer - with an adiabatic wall and with wall cooling - for Mach numbers as large as 10. Direct comparisons of the predictions of the new model with raw experimental data and with results from the K - omega model indicate that it performs well for a wide range of Mach numbers. The surprising finding is that the Morkovin hypothesis, where turbulent dilatational terms are neglected, works well at high Mach numbers, provided that the near wall model is asymptotically consistent. Instances where the model predictions deviate from the experiments appear to be attributable to the assumption of constant turbulent Prandtl number - a deficiency that will be addressed in a future paper
Rotating Leaks in the Stadium Billiard
The open stadium billiard has a survival probability, , that depends on
the rate of escape of particles through the leak. It is known that the decay of
is exponential early in time while for long times the decay follows a
power law. In this work we investigate an open stadium billiard in which the
leak is free to rotate around the boundary of the stadium at a constant
velocity, . It is found that is very sensitive to . For
certain values is purely exponential while for other values the
power law behaviour at long times persists. We identify three ranges of
values corresponding to three different responses of . It is
shown that these variations in are due to the interaction of the moving
leak with Marginally Unstable Periodic Orbits (MUPOs)
Vacuolar ATPase depletion contributes to dysregulation of endocytosis in bloodstream forms of Trypanosoma brucei
BACKGROUND
Vacuolar H-ATPase (V-ATPase) is a highly conserved protein complex which hydrolyzes ATP and pumps protons to acidify vacuolar vesicles. Beyond its role in pH maintenance, the involvement of V-ATPase in endocytosis is well documented in mammals and plants but is less clear in Trypanosoma brucei.
METHODS
In this study, the subcellular localization of V-ATPase subunit B (TbVAB) of T. brucei was assessed via in situ N-terminal YFP-tagging and immunofluorescence assays. Transgenic bloodstream forms (BSF) of T. brucei were generated which comprised either a V-ATPase subunit B (TbVAB) conditional knockout or a V-ATPase subunit A (TbVAA) knockdown. Acridine orange and BCECF-AM were employed to assess the roles of V-ATPase in the pH regulation of BSF T. brucei. The endocytic activities of three markers were also characterized by flow cytometry analyses. Furthermore, trypanosomes were counted from trypanolysis treatment groups (either containing 1% or 5% NHS) and endocytosed trypanosome lytic factor (TLF) was also analyzed by an immunoblotting assay.
RESULTS
TbVAB was found to localize to acidocalcisomes, lysosomes and probably also to endosomes of BSF of T. brucei and was demonstrated to be essential for cell growth. TbVAB depletion neutralized acidic organelles at 24 hours post-tetracycline depletion (hpd), meanwhile the steady state intracellular pH increased from 7.016 ± 0.013 to 7.422 ± 0.058. Trypanosomes with TbVAB depletion at 24 hpd were found to take up more transferrin (2.068 ± 0.277 fold) but less tomato lectin (49.31 ± 22.57%) by endocytosis, while no significant change was detected in dextran uptake. Similar endocytic dysregulated phenotypes were also observed in TbVAA knockdown cells. In addition, TbVAB depleted trypanosomes showed a low uptake of TLF and exhibited less sensitive to lysis in both 1% and 5% NHS treatments.
CONCLUSIONS
TbVAB is a key component of V-ATPase and was found to play a key function in endocytosis as well as exhibiting different effects in a receptor/cargo dependent manner in BSF of T. brucei. Besides vacuolar alkalinization, the dysregulation of endocytosis in TbVAB depleted T. brucei is considered to contribute to the reduced sensitivity to lysis by normal human serum
R-Mode Oscillations and Spindown of Young Rotating Magnetic Neutron Stars
Recent work has shown that a young, rapidly rotating neutron star loses
angular momentum to gravitational waves generated by unstable r-mode
oscillations. We study the spin evolution of a young, magnetic neutron star
including both the effects of gravitational radiation and magnetic braking
(modeled as magnetic dipole radiation). Our phenomenological description of
nonlinear r-modes is similar to, but distinct from, that of Owen et al. (1998)
in that our treatment is consistent with the principle of adiabatic invariance
in the limit when direct driving and damping of the mode are absent. We show
that, while magnetic braking tends to increase the r-mode amplitude by spinning
down the neutron star, it nevertheless reduces the efficiency of gravitational
wave emission from the star. For B >= 10^14 (\nus/300 Hz)^2 G, where \nus is
the spin frequency, the spindown rate and the gravitational waveforms are
significantly modified by the effect of magnetic braking. We also estimate the
growth rate of the r-mode due to electromagnetic (fast magnetosonic) wave
emission and due to Alfven wave emission in the neutron star magnetosphere. The
Alfven wave driving of the r-mode becomes more important than the gravitational
radiation driving when B >= 10^13 (\nus/150 Hz)^3 G; the electromagnetic wave
driving of the r-mode is much weaker. Finally, we study the properties of local
Rossby-Alfven waves inside the neutron star and show that the fractional change
of the r-mode frequency due to the magnetic field is of order 0.5 (B/10^16 G)^2
(\nus/100 Hz)^-2.Comment: 18 pages, 4 figures; ApJ, accepted (v544: Nov 20, 2000); added two
footnotes and more discussion of mode driving by Alfven wave
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