14,209 research outputs found
The use of real time digital simulation and hardware in the loop to de-risk novel control algorithms
Low power demonstrators are commonly used to validate novel control algorithms. However, the response of the demonstrator to network transients and faults is often unexplored. The importance of this work has, in the past, justified facilities such as the T45 Shore Integration Test Facility (SITF) at the Electric Ship Technology Demonstrator (ESTD). This paper presents the use of real time digital simulation and hardware in the loop to de-risk a innovative control algorithm with respect to network transients and faults. A novel feature of the study is the modelling of events at the power electronics level (time steps of circa 2 ÎĽs) and the system level (time steps of circa 50 ÎĽs)
The Distance to the Cygnus Loop from Hubble Space Telescope Imaging of the Primary Shock Front
We present a Hubble Space Telescope/WFPC2 narrow-band H-alpha image of a
region on the northeastern limb of the Cygnus Loop supernova remnant. This
location provides a detailed example of where the primary blast wave first
encounters the surrounding interstellar medium. The filament structure is seen
in exquisite detail in this image, which was obtained primarily as an EARLY
ACQuisition image for a follow-up spectroscopic program. We compare the HST
image to a digitized version of the POSS-I red plate to measure the proper
motion of this filament. By combining this value for the proper motion with
previous measurements of the shock velocity at this position we find that the
distance to the Cygnus Loop is 440 (+130, -100) pc, considerably smaller than
the canonical value of 770 pc. We briefly discuss the ramifications of this new
distance estimate for our understanding of this prototypical supernova remnant.Comment: 18 pages, 3 Figures (2 JPEG and one Postscript
Abundant and equipotent founder cells establish and maintain acute lymphoblastic leukaemia
High frequencies of blasts in primary acute lymphoblastic leukaemia (ALL) samples have the potential to induce leukaemia and to engraft mice. However, it is unclear how individual ALL cells each contribute to drive leukaemic development in a bulk transplant and the extent to which these blasts vary functionally. We used cellular barcoding as a fate mapping tool to track primograft ALL blasts in vivo. Our results show that high numbers of ALL founder cells contribute at similar frequencies to leukaemic propagation over serial transplants, without any clear evidence of clonal succession. These founder cells also exhibit equal capacity to home and engraft to different organs, although stochastic processes may alter the composition in restrictive niches. Our findings enhance the stochastic stem cell model of ALL by demonstrating equal functional abilities of singular ALL blasts and show that successful treatment strategies must eradicate the entire leukaemic cell population
Peristaltic Transport of a Couple Stress Fluid: Some Applications to Hemodynamics
The present paper deals with a theoretical investigation of the peristaltic
transport of a couple stress fluid in a porous channel. The study is motivated
towards the physiological flow of blood in the micro-circulatory system, by
taking account of the particle size effect. The velocity, pressure gradient,
stream function and frictional force of blood are investigated, when the
Reynolds number is small and the wavelength is large, by using appropriate
analytical and numerical methods. Effects of different physical parameters
reflecting porosity, Darcy number, couple stress parameter as well as amplitude
ratio on velocity profiles, pumping action and frictional force, streamlines
pattern and trapping of blood are studied with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in good agreement with those of Shapiro et. al \cite{r25} that was carried
out for a non-porous channel in the absence of couple stress effect. The
present study puts forward an important observation that for peristaltic
transport of a couple stress fluid during free pumping when the couple stress
effect of the fluid/Darcy permeability of the medium, flow reversal can be
controlled to a considerable extent. Also by reducing the permeability it is
possible to avoid the occurrence of trapping phenomenon
Determining the Efficacy of Predicting Beef Tenderness Using Proteins from Purge
Objective: To determine if proteins from purge can predict tenderness at different aging points as a nondestructive method
Altered rainfall patterns increase forb abundance and richness in native tallgrass prairie
Citation: Jones, S. K., Collins, S. L., Blair, J. M., Smith, M. D., & Knapp, A. K. (2016). Altered rainfall patterns increase forb abundance and richness in native tallgrass prairie. Scientific Reports, 6, 10. doi:10.1038/srep20120Models predict that precipitation variability will increase with climate change. We used a 15-year precipitation manipulation experiment to determine if altering the timing and amount of growing season rainfall will impact plant community structure in annually burned, native tallgrass prairie. The altered precipitation treatment maintained the same total growing season precipitation as the ambient precipitation treatment, but received a rainfall regime of fewer, larger rain events, and longer intervals between events each growing season. Although this change in precipitation regime significantly lowered mean soil water content, overall this plant community was remarkably resistant to altered precipitation with species composition relatively stable over time. However, we found significantly higher forb cover and richness and slightly lower grass cover on average with altered precipitation, but the forb responses were manifest only after a ten-year lag period. Thus, although community structure in this grassland is relatively resistant to this type of altered precipitation regime, forb abundance in native tallgrass prairie may increase in a future characterized by increased growing season precipitation variability
Beam Profile Measurements and Simulations of the PETRA Laser-Wire
The Laser-wire will be an essential diagnostic tool at the International
Linear Collider. It uses a finely focussed laser beam to measure the transverse
profile of electron bunches by detecting the Compton-scattered photons (or
degraded electrons) downstream of where the laser beam intersects the electron
beam. Such a system has been installed at the PETRA storage ring at DESY, which
uses a piezo-driven mirror to scan the laser-light across the electron beam.
Lat- est results of experimental data taking are presented and compared to
detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle
Accelerator Conference 2005 (PAC05
The Far-Ultraviolet Spectrum and Short Timescale Variability of AM Herculis from Observations with the Hopkins Ultraviolet Telescope
Using the Hopkins Ultraviolet Telescope (HUT), we have obtained 850-1850
angstrom spectra of the magnetic cataclysmic variable star AM Her in the high
state. These observations provide high time resolution spectra of AM Her in the
FUV and sample much of the orbital period of the system. The spectra are not
well-modelled in terms of simple white dwarf (WD) atmospheres, especially at
wavelengths shortward of Lyman alpha. The continuum flux changes by a factor of
2 near the Lyman limit as a function of orbital phase; the peak fluxes are
observed near magnetic phase 0.6 when the accreting pole of the WD is most
clearly visible. The spectrum of the hotspot can be modelled in terms of a 100
000 K WD atmosphere covering 2% of the WD surface. The high time resolution of
the HUT data allows an analysis of the short term variability and shows the UV
luminosity to change by as much as 50% on timescales as short as 10 s. This
rapid variability is shown to be inconsistent with the clumpy accretion model
proposed to account for the soft X-ray excess in polars. We see an increase in
narrow line emission during these flares when the heated face of the secondary
is in view. The He II narrow line flux is partially eclipsed at secondary
conjunction, implying that the inclination of the system is greater than 45
degrees. We also present results from models of the heated face of the
secondary. These models show that reprocessing on the face of the secondary
star of X-ray/EUV emission from the accretion region near the WD can account
for the intensities and kinematics of most of the narrow line components
observed.Comment: 19 pp., 12 fig., 3 tbl. To appear in The Astrophysical Journal. Also
available at http://greeley.pha.jhu.edu/papers/amherpp.ps.g
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