5,741 research outputs found
Piloted-simulation study of effects of vortex flaps on low-speed handling qualities of a Delta-wing airplane
A piloted-simulation study was conducted to investigate the effects of vortex flaps on low-speed handling qualities of a delta-wing airplane. The simulation math model was developed from wind tunnel tests of a 0.15 scale model of the F-106B airplane. Pilot evaluations were conducted using a six-degree-of-freedom motion base simulator. The results of the investigation showed that the reduced static longitudinal stability caused by the vortex flaps significantly degraded handling qualities in the approach-to-landing task. Acceptable handling qualities could be achieved by limiting the aft center-of-gravity location, consequently reducing the operational envelope of the airplane. Further improvement were possible by modifying the flight control force-feel system to reduce pitch-control sensitivity
Malaria elimination campaigns in the Lake Kariba region of Zambia: a spatial dynamical model
Background As more regions approach malaria elimination, understanding how
different interventions interact to reduce transmission becomes critical. The
Lake Kariba area of Southern Province, Zambia, is part of a multi-country
elimination effort and presents a particular challenge as it is an
interconnected region of variable transmission intensities.
Methods In 2012-13, six rounds of mass-screen-and-treat drug campaigns were
carried out in the Lake Kariba region. A spatial dynamical model of malaria
transmission in the Lake Kariba area, with transmission and climate modeled at
the village scale, was calibrated to the 2012-13 prevalence survey data, with
case management rates, insecticide-treated net usage, and drug campaign
coverage informed by surveillance. The model was used to simulate the effect of
various interventions implemented in 2014-22 on reducing regional transmission,
achieving elimination by 2022, and maintaining elimination through 2028.
Findings The model captured the spatio-temporal trends of decline and rebound
in malaria prevalence in 2012-13 at the village scale. Simulations predicted
that elimination required repeated mass drug administrations coupled with
simultaneous increase in net usage. Drug campaigns targeted only at high-burden
areas were as successful as campaigns covering the entire region.
Interpretation Elimination in the Lake Kariba region is possible through
coordinating mass drug campaigns with high-coverage vector control. Targeting
regional hotspots is a viable alternative to global campaigns when human
migration within an interconnected area is responsible for maintaining
transmission in low-burden areas
Neighborhood size-effects shape growing population dynamics in evolutionary public goods games
An evolutionary game emerges when a subset of individuals incur costs to provide benefits to all individuals. Public goods games (PGG) cover the essence of such dilemmas in which cooperators are prone to exploitation by defectors. We model the population dynamics of a non-linear\ua0PGG and consider density-dependence on the global level, while the game occurs within local neighborhoods. At low cooperation, increases in the public good provide increasing returns. At high cooperation, increases provide diminishing returns. This mechanism leads to diverse evolutionarily stable strategies, including monomorphic and polymorphic populations, and neighborhood-size-driven state changes, resulting in hysteresis between equilibria. Stochastic or strategy-dependent variations in neighborhood sizes favor coexistence by destabilizing monomorphic states. We integrate our model with experiments of cancer cell growth and confirm that our framework describes PGG dynamics observed in cellular populations. Our findings advance the understanding of how neighborhood-size effects in PGG shape the dynamics of growing populations. \ua9 2019, The Author(s)
Hemodynamic and vascular characteristics of DUP 753: A specific angiotensin II antagonist, in the spontaneously hypertensive rat (SHR)
State-Dependent Architecture of Thalamic Reticular Subnetworks
Behavioral state is known to influence interactions between thalamus and cortex, which are important for sensation, action, and cognition. The thalamic reticular nucleus (TRN) is hypothesized to regulate thalamo-cortical interactions, but the underlying functional architecture of this process and its state dependence are unknown. By combining the first TRN ensemble recording with psychophysics and connectivity-based optogenetic tagging, we found reticular circuits to be composed of distinct subnetworks. While activity of limbic-projecting TRN neurons positively correlates with arousal, sensory-projecting neurons participate in spindles and show elevated synchrony by slow waves during sleep. Sensory-projecting neurons are suppressed by attentional states, demonstrating that their gating of thalamo-cortical interactions is matched to behavioral state. Bidirectional manipulation of attentional performance was achieved through subnetwork-specific optogenetic stimulation. Together, our findings provide evidence for differential inhibition of thalamic nuclei across brain states, where the TRN separately controls external sensory and internal limbic processing facilitating normal cognitive function.National Institute of Neurological Disorders and Stroke (U.S.) (NIH Pathway to Independence Career Award K99 NS 078115)Brain & Behavior Research Foundation (Young Investigator Award)National Institutes of Health (U.S.) ( Transformative R01 Award TR01-GM10498)National Institutes of Health (U.S.) (Grant R01-MH061976
The Solar Neighborhood XIII: Parallax Results from the CTIOPI 0.9-m Program -- Stars with mu >= 1"/year (MOTION Sample)
We present the first set of definitive trigonometric parallaxes and proper
motions from the Cerro Tololo Inter-American Observatory Parallax Investigation
(CTIOPI). Full astrometric reductions for the program are discussed, including
methods of reference stars selection, differential color refraction
corrections, and conversion of relative to absolute parallax. Using data
acquired at the 0.9-m at CTIO, full astrometric solutions and
photometry are presented for 36 red and white dwarf stellar systems with proper
motions faster than 1\farcs0/yr. Of these, thirty three systems have the first
ever trigonometric parallaxes, which comprise 41% of MOTION systems (those with
proper motions greater than 1\farcs0/yr) south of 0 that have no
parallaxes. Four of the systems are new members of the RECONS 10 pc sample for
which the first accurate trigonometric parallaxes are published here: DENIS
J1048-3956 (4.04 0.03 pc), GJ 1128 (LHS 271, 6.53 0.10 pc), GJ 1068
(LHS 22, 6.97 0.09 pc), and GJ 1123 (LHS 263, 9.02 0.16 pc). In
addition, two red subdwarf-white dwarf pairs, LHS 193AB and LHS 300AB, are
identified. The white dwarf secondaries fall in a previously uncharted region
of the HR diagram.Comment: 40 pages, 7 figures, accepted to The Astronomical Journal (scheduled
for April 2005 issue), Re-submit, Table 2 running off the bottom of the page
has been fixe
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We All Want More Teachers of Color, Right?: Concerns and Considerations about the Emergent Consensus
There is a near unanimity among researchers and practitioners about the need to recruit and retain more teachers of color. Diversification of the teaching ranks has clear benefits. This brief contends that the push for diversifying the teaching force must be scrutinized within the context of larger patterns and structures of racial injustice, and should be pursued as part of broader efforts toward equity-oriented school reform. The authors offer questions that those concerned with the diversification of the teaching force might consider as safeguards to promote a focus on strategic essentialism and the transformation of schools.</p
Design of University Small-Scale Dairy Processing Facility
This project was assigned to research the feasibility and value of implementing a dairy processing facility on the campus of the University of Nebraska-Lincoln. The facility would process milk produced from cows under the same roof and will serve as an educational experience for Nebraska dairy farmers, UNL students, and K-12 students in the Lincoln-Lancaster County area. If the project is successful and replicated across the state, this facility could have a significant impact on the reduction of milk transportation costs in the Nebraska dairy industry.
The project began with researching milk processing methods and steps from production to consumption. Shortly after this step, information on milk consumption patterns was collected from UNL Dining Services to determine demand on campus. Every unit operation requires certain equipment to effectively ensure the safety and quality of the final product, and mass balances from UNL milk consumption data were used to size equipment and storage capacity. Engineering firms were then consulted to gather information on equipment specifications and prices. Equipment costs and operating costs (estimated with the help of Dr. Howell and other university dairy operations) were entered into a Monte Carlo simulation to analyze return on investment and a breakeven point.
The results from the costs section showed that the fixed costs (equipment and engineering) for the milk processing would be about $1.2 million. The Monte Carlo simulation showed that the project would not turn a profit for 10-12 years, and approximately 2.25 million gallons of milk would need to be processed and sold to recover initial costs. Overall, the project successfully displays data that can be interpreted by the client to decide whether to move forward with the project and the appropriate scale for the project at UNL
Variability in the Thermal Emission from Accreting Neutron Star Transients
The composition of the outer 100 m of a neutron star sets the heat flux that
flows outwards from the core. For an accreting neutron star in an X-ray
transient, the thermal quiescent flux depends sensitively on the amount of
hydrogen and helium remaining on the surface after an accretion outburst and on
the composition of the underlying ashes of previous H/He burning. Because H/He
has a higher thermal conductivity, a larger mass of H/He implies a shallower
thermal gradient through the low density envelope and hence a higher effective
temperature for a given core temperature. The mass of residual H and He varies
from outburst to outburst, so the thermal quiescent flux is variable even
though the core temperature is constant for timescales < 10 000 yr. Heavy
elements settle from a H/He envelope in a few hours; we therefore model the
quiescent envelope as two distinct layers, H/He over heavier elements, and
treat the mass of H/He as a free parameter. We find that the emergent thermal
quiescent flux can vary by a factor of 2 to 3 between different quiescent
epochs. The variation is more pronounced at lower interior temperatures, making
systems with low quiescent luminosities and frequent outbursts, such as SAX
J1808.4-3658, ideal candidates from which to observe this effect. We compute,
for different ash compositions, the interior temperatures of Cen X-4, Aql X-1,
and SAX J1808.4-3658. In the case of Aql X-1, the inferred high interior
temperature suggests that neutrino cooling contributes to the neutron star's
thermal balance.Comment: 14 pages, 5 figures, uses emulateapj5 and psnfss fonts. To be
published in The Astrophysical Journa
The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31 Halo with Blue Horizontal Branch Stars
We attempt to constrain the shape of M31's inner stellar halo by tracing the
surface density of blue horizontal branch (BHB) stars at galactocentric
distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved
stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury
(PHAT) survey, supplemented by several archival Hubble Space Telescope
observations. We find that the ratio of BHB to red giant stars is relatively
constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of
the halo population as the red giant branch. In the inner halo, we do not
expect BHB stars to be produced by the high metallicity bulge and disk, making
BHB stars a good candidate to be a reliable tracer of the stellar halo to much
smaller galactocentric distances. If we assume a power-law profile r^(-\alpha)
for the 2-D projected surface density BHB distribution, we obtain a
high-quality fit with a 2-D power-law index of \alpha=2.6^{+0.3}_{-0.2} outside
of 3 kpc, which flattens to \alpha<1.2 inside of 3 kpc. This slope is
consistent with previous measurements but is anchored to a radial baseline that
extends much farther inward. Finally, assuming azimuthal symmetry and a
constant mass-to-light ratio, the best-fitting profile yields a total halo
stellar mass of 2.1^{+1.7}_{-0.4} x 10^9 M_sun. These properties are comparable
with both simulations of stellar halo formation formed by satellite disruption
alone, and with simulations that include some in situ formation of halo stars.Comment: 15 pages, 1 table, 5 figures, accepted for publication in Ap
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