63,494 research outputs found
Small Payload Flight Systems (SPFS)
The Small Payload Flight System (SPFS) provides a simple and cost-effective approach to carrying small size experiments on the space shuttle. The system uses a bridge-like structure which spans the orbiter cargo bay but is only 3 feet in length. The structure can carry up to 4300 lb of payload weight and can be positioned at any location along the length of the cargo bay. In addition to the structural support, the SPFS provides avionics services to experiments. These include electrical power distribution and control, command and telemetry for control of the experiments and subsystem health monitoring, and software computations. The avionics system includes a flight qualified electrical power branching distributor, and a system control unit based on the Intel 8086 microprocessor. Data can be recorded on magnetic tape or transmitted to the ground. Finally, a Freon pump and cold plate system provides environmental control for both the avionics hardware and the experiments as necessary
Mode-locking in advection-reaction-diffusion systems: an invariant manifold perspective
Fronts propagating in two-dimensional advection-reaction-diffusion (ARD)
systems exhibit rich topological structure. When the underlying fluid flow is
periodic in space and time, the reaction front can lock to the driving
frequency. We explain this mode-locking phenomenon using so-called burning
invariant manifolds (BIMs). In fact, the mode-locked profile is delineated by a
BIM attached to a relative periodic orbit (RPO) of the front element dynamics.
Changes in the type (and loss) of mode-locking can be understood in terms of
local and global bifurcations of the RPOs and their BIMs. We illustrate these
concepts numerically using a chain of alternating vortices in a channel
geometry.Comment: 9 pages, 13 figure
Thousand Aviator Study - Nonvestibular Contributions to Postural Equilibrium Functions
Psychomotor performance and postural equilibrium functioning defined by quantitative ataxia test battery, and relation to pilot selection and gerontolog
Fractal templates in the escape dynamics of trapped ultracold atoms
We consider the dynamic escape of a small packet of ultracold atoms launched
from within an optical dipole trap. Based on a theoretical analysis of the
underlying nonlinear dynamics, we predict that fractal behavior can be seen in
the escape data. This data would be collected by measuring the time-dependent
escape rate for packets launched over a range of angles. This fractal pattern
is particularly well resolved below the Bose-Einstein transition temperature--a
direct result of the extreme phase space localization of the condensate. We
predict that several self-similar layers of this novel fractal should be
measurable and we explain how this fractal pattern can be predicted and
analyzed with recently developed techniques in symbolic dynamics.Comment: 11 pages with 5 figure
A Generic Algorithm for IACT Optical Efficiency Calibration using Muons
Muons produced in Extensive Air Showers (EAS) generate ring-like images in
Imaging Atmospheric Cherenkov Telescopes when travelling near parallel to the
optical axis. From geometrical parameters of these images, the absolute amount
of light emitted may be calculated analytically. Comparing the amount of light
recorded in these images to expectation is a well established technique for
telescope optical efficiency calibration. However, this calculation is usually
performed under the assumption of an approximately circular telescope mirror.
The H.E.S.S. experiment entered its second phase in 2012, with the addition of
a fifth telescope with a non-circular 600m mirror. Due to the differing
mirror shape of this telescope to the original four H.E.S.S. telescopes,
adaptations to the standard muon calibration were required. We present a
generalised muon calibration procedure, adaptable to telescopes of differing
shapes and sizes, and demonstrate its performance on the H.E.S.S. II array.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
The ‘EDHF’ Antagonist 14, 15 Epoxyeicosa-5(Z)-Enoic Acid has Vasodilator Properties in Mesenteric Vessels
There is now overwhelming evidence for Epoxyeicosatrienoic acids (EETs) as endothelial derived hyperpolarising factor (EDHF). Most recently, a number of pharmacological tools have been developed for the study of EETs in relation to EDHF responses. EETs have been shown to cause relaxation by activating smooth muscle large conductance Ca2+ sensitive K+ (BKCa) (Archer et al, 2003). This dilatory response has been shown to be specifically inhibited by its analogue 14, 15-epoxyeicosa-5 (Z) enoic acid (14, 15 EEZE) in both human internal mammary artery and bovine coronary artery (Archer et al, 2003). Here we have investigated the antagonist effects of 14, 15 EEZE in murine arteries. Male Black 6 mice (12-18 weeks) were killed by lethal exposure to CO2. First order arteries were isolated and mounted in wire myographs immersed in physiological salt solution (PSS). Arteries were equilibrated (30 mins) and tensions normalised as described previously (Mulvany and Halpern, 1977). Arteries incubated for 30 minutes with or without 3µg/ml 14, 15 EEZE. A concentration response curve to 11, 12 EET was performed cumulatively on arteries pre-contracted with EC80 U46619. In some experiments, arteries were pre-contracted with EC80 U46619, and concentration response to 14, 15 EEZE performed cumulatively.Non peer reviewe
Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy
In radio astronomy, reference signals from auxiliary antennas that receive
only the radio frequency interference (RFI) can be modified to model the RFI
environment at the astronomy receivers. The RFI can then be canceled from the
astronomy signal paths. However, astronomers typically only require signal
statistics. If the RFI statistics are changing slowly, the cancellation can be
applied to the signal correlations at a much lower rate than is required for
standard adaptive filters. In this paper we describe five canceler setups;
precorrelation and postcorrelation cancelers that use one or two reference
signals in different ways. The theoretical residual RFI and added noise levels
are examined and are demonstrated using microwave television RFI at the
Australia Telescope Compact Array. The RFI is attenuated to below the system
noise, a reduction of at least 20 dB. While dual-reference cancelers add more
reference noise than single-reference cancelers, this noise is zero-mean and
only adds to the system noise, decreasing the sensitivity. The residual RFI
that remains in the output of single-reference cancelers (but not
dual-reference cancelers) sets a nonzero noise floor that does not act like
random system noise and may limit the achievable sensitivity. Thus,
dual-reference cancelers often result in superior cancellation. Dual-reference
precorrelation cancelers require a double-canceler setup to be useful and to
give equivalent results to dual-reference postcorrelation cancelers.Comment: 11 pages created using emulateap
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