30,066 research outputs found
The drag of a body moving transversely in a confined stratified fluid
The slow motion of a body through a stratified fluid bounded laterally by insulating walls is studied for both large and small Peclet number. The Taylor column and its associated boundary and shear layers are very different from the analogous problem in a rotating fluid. In particular, the large Peclet number problem is non-linear and exhibits mixing of statically unstable fluid layers, and hence the drag is order one; whereas the small Peclet number flow is everywhere stable, and the drag is of the order of the Peclet number
Left seat command or leadership flight, leadership training and research at North Central Airlines
The need for flight leadership training for flight deck crewmembers is addressed. A management grid is also described which provides a quantitative management language against which any number of management behaviors can be measured
The effects of spacecraft environments on some hydrolytic enzyme patterns in bacteria
The effects of space flight on the production and characteristics of proteolytic enzymes are studied for a number of bacterial species isolated from crew members and spacecraft. Enzymatic make-up and cultural characteristics of bacteria isolated from spacecraft crew members are determined. The organism Aeromonas proteolytica and the proteolytic enzymes which it produces are used as models for future spacecraft experiments
A fast and robust numerical scheme for solving models of charge carrier transport and ion vacancy motion in perovskite solar cells
Drift-diffusion models that account for the motion of both electronic and
ionic charges are important tools for explaining the hysteretic behaviour and
guiding the development of metal halide perovskite solar cells. Furnishing
numerical solutions to such models for realistic operating conditions is
challenging owing to the extreme values of some of the parameters. In
particular, those characterising (i) the short Debye lengths (giving rise to
rapid changes in the solutions across narrow layers), (ii) the relatively large
potential differences across devices and (iii) the disparity in timescales
between the motion of the electronic and ionic species give rise to significant
stiffness. We present a finite difference scheme with an adaptive time step
that is posed on a non-uniform staggered grid that provides second order
accuracy in the mesh spacing. The method is able to cope with the stiffness of
the system for realistic parameters values whilst providing high accuracy and
maintaining modest computational costs. For example, a transient sweep of a
current-voltage curve can be computed in only a few minutes on a standard
desktop computer.Comment: 22 pages, 8 figure
Using baseline-dependent window functions for data compression and field-of-interest shaping in radio interferometry
In radio interferometry, observed visibilities are intrinsically sampled at
some interval in time and frequency. Modern interferometers are capable of
producing data at very high time and frequency resolution; practical limits on
storage and computation costs require that some form of data compression be
imposed. The traditional form of compression is a simple averaging of the
visibilities over coarser time and frequency bins. This has an undesired side
effect: the resulting averaged visibilities "decorrelate", and do so
differently depending on the baseline length and averaging interval. This
translates into a non-trivial signature in the image domain known as
"smearing", which manifests itself as an attenuation in amplitude towards
off-centre sources. With the increasing fields of view and/or longer baselines
employed in modern and future instruments, the trade-off between data rate and
smearing becomes increasingly unfavourable. In this work we investigate
alternative approaches to low-loss data compression. We show that averaging of
the visibility data can be treated as a form of convolution by a boxcar-like
window function, and that by employing alternative baseline-dependent window
functions a more optimal interferometer smearing response may be induced. In
particular, we show improved amplitude response over a chosen field of
interest, and better attenuation of sources outside the field of interest. The
main cost of this technique is a reduction in nominal sensitivity; we
investigate the smearing vs. sensitivity trade-off, and show that in certain
regimes a favourable compromise can be achieved. We show the application of
this technique to simulated data from the Karl G. Jansky Very Large Array (VLA)
and the European Very-long-baseline interferometry Network (EVN)
Analog of the Clauser-Horne-Shimony-Holt inequality for steering
The Clauser-Horne-Shimony-Holt (CHSH) inequality (and its permutations), are
necessary and sufficient criteria for Bell nonlocality in the simplest
Bell-nonlocality scenario: 2 parties, 2 measurements per party and 2 outcomes
per measurement. Here we derive an inequality for EPR-steering that is an
analogue of the CHSH, in that it is necessary and sufficient in this same
scenario. However, since in the case of steering the device at Bob's site must
be specified (as opposed to the Bell case in which it is a black box), the
scenario we consider is that where Alice performs two (black-box) dichotomic
measurements, and Bob performs two mutually unbiased qubit measurements. We
show that this inequality is strictly weaker than the CHSH, as expected, and
use it to decide whether a recent experiment [Phys. Rev. Lett. 110, 130401
(2013).] involving a single-photon split between two parties has demonstrated
EPR-steering.Comment: Expanded v2, new results, new figure. 9 pages, 2 figure
Rocket ozone sounding network data
During the period December 1976 through February 1977, three regular monthly ozone profiles were measured at Wallops Flight Center, two special soundings were taken at Antigua, West Indies, and at the Churchill Research Range, monthly activities were initiated to establish stratospheric ozone climatology. This report presents the data results and flight profiles for the period covered
- …