1,081 research outputs found
Free-flight model investigation of a vertical-attitude VTOL fighter with twin vertical tails
Free-flight tests were conducted in the Langley full-scale tunnel to determine the stability and control characteristics of a vertical-attitude VTOL fighter having twin vertical tails and a pivoted fuselage forebody (nose-cockpit) arrangement. The flight tests included hovering flights and transition flights from hover to conventional forward flight. Static force tests were also made to aid in the analysis of the flight tests. The model exhibited satisfactory stability and control characteristics, and the transition from hovering flight to conventional forward flight was relatively smooth and straightforward
Evaluation of the Use of UAV-Derived Vegetation Indices and Environmental Variables for Grapevine Water Status Monitoring Based on Machine Learning Algorithms and SHAP Analysis
(c) The Author/sfals
Evaluation of Point Hyperspectral Reflectance and Multivariate Regression Models for Grapevine Water Status Estimation
Publishe
Citrus growers vary in their adoption of biological control
In a spring 2010 survey, we investigated the characteristics that influenced whether California growers controlled major citrus pests with beneficial insects. We also performed statistical analysis of growers' reliance on Aphytus melinus, a predatory wasp, to control California red scale. The survey results suggest that growers with greater citrus acreage and more education are more likely to use biological control. Marketing outlets, ethnicity and primary information sources also influenced the extent of reliance on beneficial insects. In Probit model analysis, respondents with greater citrus acreage were more likely to incorporate A. melinus into their pest management, as well as those with more education and higher-valued crops. Information sources and growing region also had statistically significant effects
Controllability of structural brain networks.
Cognitive function is driven by dynamic interactions between large-scale neural circuits or networks, enabling behaviour. However, fundamental principles constraining these dynamic network processes have remained elusive. Here we use tools from control and network theories to offer a mechanistic explanation for how the brain moves between cognitive states drawn from the network organization of white matter microstructure. Our results suggest that densely connected areas, particularly in the default mode system, facilitate the movement of the brain to many easily reachable states. Weakly connected areas, particularly in cognitive control systems, facilitate the movement of the brain to difficult-to-reach states. Areas located on the boundary between network communities, particularly in attentional control systems, facilitate the integration or segregation of diverse cognitive systems. Our results suggest that structural network differences between cognitive circuits dictate their distinct roles in controlling trajectories of brain network function
Medial Temporal Lobe BOLD Activity at Rest Predicts Individual Differences in Memory Ability in Hhealthy Young Adults
Human beings differ in their ability to form and retrieve lasting long-term memories. To explore the source of these individual differences, we used functional magnetic resonance imaging to measure blood-oxygen-level-dependent (BOLD) activity in healthy young adults (n = 50) during periods of resting fixation that were interleaved with periods of simple cognitive tasks. We report that medial temporal lobe BOLD activity during periods of rest predicts individual differences in memory ability. Specifically, individuals who exhibited greater magnitudes of task-induced deactivations in medial temporal lobe BOLD signal (as compared to periods of rest) demonstrated superior memory during offline testing. This relationship was independent of differences in general cognitive function and persisted across different control tasks (i.e., number judgment versus checkerboard detection) and experimental designs (i.e., blocked versus event-related). These results offer a neurophysiological basis for the variability in mnemonic ability that is present amongst healthy young adults and may help to guide strategies aimed at early detection and intervention of neurological and mnemonic impairment
Medial Temporal Lobe BOLD Activity at Rest Predicts Individual Differences in Memory Ability in Hhealthy Young Adults
Human beings differ in their ability to form and retrieve lasting long-term memories. To explore the source of these individual differences, we used functional magnetic resonance imaging to measure blood-oxygen-level-dependent (BOLD) activity in healthy young adults (n = 50) during periods of resting fixation that were interleaved with periods of simple cognitive tasks. We report that medial temporal lobe BOLD activity during periods of rest predicts individual differences in memory ability. Specifically, individuals who exhibited greater magnitudes of task-induced deactivations in medial temporal lobe BOLD signal (as compared to periods of rest) demonstrated superior memory during offline testing. This relationship was independent of differences in general cognitive function and persisted across different control tasks (i.e., number judgment versus checkerboard detection) and experimental designs (i.e., blocked versus event-related). These results offer a neurophysiological basis for the variability in mnemonic ability that is present amongst healthy young adults and may help to guide strategies aimed at early detection and intervention of neurological and mnemonic impairment
Photoionisation Modelling of the X-ray Emission Line Regions within the Seyfert 2 AGN NGC 1068
We investigate the photoionised X-ray emission line regions (ELRs) within the
Seyfert 2 galaxy NGC 1068, to determine if there are any characteristic changes
between observations taken fourteen years apart. We compare XMM-Newton
observations collected in 2000 and 2014, simultaneously fitting the reflection
grating spectrometer (RGS) and EPIC-pn spectra of each epoch, for the first
time, with the photoionisation model, PION, in SPEX. We find that four PION
components are required to fit the majority of the emission lines in the
spectra of NGC 1068, with , , and
to for both epochs. Comparing the ionisation
state of the components shows almost no difference between the two epochs,
while there is an increase in the total column density. To estimate the
locations of these plasma regions from the central black hole we compare
distance methods, excluding the variability arguments as there is no spectral
change between observations. Although the methods are unable to constrain the
distances, the locations are consistent with the narrow line region, with the
possibility of the higher ionised component being part of the broad line
region, but we cannot conclude this for certain. In addition, we find evidence
for emission from collisionally ionised plasma, while previous analysis had
suggested that collisional plasma emission was unlikely. However, although PION
is unable to account for the FeXVII emission lines at 15 and 17 \AA, we do not
rule out that photoexcitation is a valid processes to produce these lines too.
NGC 1068 has not changed, both in terms of the observed spectra or from our
modelling, within the 14 year time period between observations. This suggests
that the ELRs are fairly static relative to the 14 year time frame between
observations, or there is no dramatic change in the black hole variability.Comment: 19 pages, 10 figure
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