2,472 research outputs found
Study of liquid jet impingement on screens
A model is presented for an unconfined flow, such as a free jet, impinging on a screen which incorporates the influence of liquid deflection by the screen. The boundary layer blockage coefficient is introduced. This coefficient depends on the screen weave geometry and the jet impingement angle, and essentially accounts for the increase in fluid particle trajectory length through the screen resulting from the flow deflection. Comparisons were made with previous experimental studies to determine empirical values of the blockage coefficient. It is concluded that the new model reliably predicts the bulk flow and penetration characteristics of an impinging liquid jet interacting with a screen
The Impact of Type Ia Supernova Ejecta on Binary Companions
We present adaptive mesh refinement (AMR) hydrodynamical simulations of the
interaction between Type Ia supernovae and their companion stars within the
context of the single-degenerate model. Results for 3D red-giant companions
without binary evolution agree with previous 2D results by Marietta et al. We
also consider evolved helium-star companions in 2D. For a range of helium-star
masses and initial binary separations, we examine the mass unbound by the
interaction and the kick velocity delivered to the companion star. We find that
unbound mass versus separation obeys a power law with index between -3.1 and
-4.0, consistent with previous results for hydrogen-rich companions. Kick
velocity also obeys a power-law relationship with binary separation, but the
slope differs from those found for hydrogen-rich companions. Assuming accretion
via Roche-lobe overflow, we find that the unbound helium mass is consistent
with observational limits. Ablation (shock heating) appears to be more
important in removing gas from helium-star companions than from hydrogen-rich
ones, though stripping (momentum transfer) dominates in both cases.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers" at Mykonos,
Greece, June 22-25, 201
Robust Emergent Activity in Dynamical Networks
We study the evolution of a random weighted network with complex nonlinear
dynamics at each node, whose activity may cease as a result of interactions
with other nodes. Starting from a knowledge of the micro-level behaviour at
each node, we develop a macroscopic description of the system in terms of the
statistical features of the subnetwork of active nodes. We find the asymptotic
characteristics of this subnetwork to be remarkably robust: the size of the
active set is independent of the total number of nodes in the network, and the
average degree of the active nodes is independent of both the network size and
its connectivity. These results suggest that very different networks evolve to
active subnetworks with the same characteristic features. This has strong
implications for dynamical networks observed in the natural world, notably the
existence of a characteristic range of links per species across ecological
systems.Comment: 4 pages, 5 figure
Rapid fluctuations in the high-energy X-ray flux from a source in Crux
Balloonborne X ray telescopic observations of two point sources in Cru
A q-deformed nonlinear map
A scheme of q-deformation of nonlinear maps is introduced. As a specific
example, a q-deformation procedure related to the Tsallis q-exponential
function is applied to the logistic map. Compared to the canonical logistic
map, the resulting family of q-logistic maps is shown to have a wider spectrum
of interesting behaviours, including the co-existence of attractors -- a
phenomenon rare in one dimensional maps.Comment: 17 pages, 19 figure
Event-driven charge-coupled device design and applications therefor
An event-driven X-ray CCD imager device uses a floating-gate amplifier or other non-destructive readout device to non-destructively sense a charge level in a charge packet associated with a pixel. The output of the floating-gate amplifier is used to identify each pixel that has a charge level above a predetermined threshold. If the charge level is above a predetermined threshold the charge in the triggering charge packet and in the charge packets from neighboring pixels need to be measured accurately. A charge delay register is included in the event-driven X-ray CCD imager device to enable recovery of the charge packets from neighboring pixels for accurate measurement. When a charge packet reaches the end of the charge delay register, control logic either dumps the charge packet, or steers the charge packet to a charge FIFO to preserve it if the charge packet is determined to be a packet that needs accurate measurement. A floating-diffusion amplifier or other low-noise output stage device, which converts charge level to a voltage level with high precision, provides final measurement of the charge packets. The voltage level is eventually digitized by a high linearity ADC
Evaluating techniques for sampling stream crayfish (paranephrops planifrons)
We evaluated several capture and analysis techniques for estimating abundance and size structure of freshwater crayfish (Paranephrops planifrons) (koura) from a forested North Island, New Zealand stream to provide a methodological basis for future population studies. Direct observation at night and collecting with baited traps were not considered useful. A quadrat sampler was highly biased toward collecting small individuals. Handnetting at night and estimating abundances using the depletion method were not as efficient as handnetting on different dates and analysing by a mark-recapture technique. Electrofishing was effective in collecting koura from different habitats and resulted in the highest abundance estimates, and mark-recapture estimates appeared to be more precise than depletion estimates, especially if multiple recaptures were made. Handnetting captured more large crayfish relative to electrofishing or the quadrat sampler
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