1,805 research outputs found
Effect of ambient temperature during acute aerobic exercise on short-term appetite, energy intake, and plasma acylated ghrelin in recreationally active males
Ambient temperature during exercise may affect energy intake regulation. Compared with a temperate (20 °C) environment, 1 h of running followed by 6 h of rest tended to decrease energy intake from 2 ad libitum meals in a hot (30 °C) environment but increase energy intake in a cool (10 °C) environment (p = 0.08). Core temperature changes did not appear to mediate this trend; whether acylated ghrelin is involved is unclear. Further research is warranted to clarify these findings
A comparison of methods for assessing power output in nonâuniform onshore wind farms
Wind resource assessments are used to estimate a wind farmâs power production during the planning process. It is important that these estimates are accurate, as they can impact financing agreements, transmission planning, and environmental targets. Here, we analyze the challenges in wind power estimation for onshore farms. Turbine wake effects are a strong determinant of farm power production. With given input wind conditions, wake losses typically cause downstream turbines to produce significantly less power than upstream turbines. These losses have been modeled extensively and are well understood under certain conditions. Most notably, validation of different model types has favored offshore farms. Models that capture the dynamics of offshore wind conditions do not necessarily perform equally as well for onshore wind farms. We analyze the capabilities of several different methods for estimating wind farm power production in 2 onshore farms with nonâuniform layouts. We compare the Jensen model to a number of statistical models, to meteorological downscaling techniques, and to using no model at all. We show that the complexities of some onshore farms result in wind conditions that are not accurately modeled by the Jensen wake decay techniques and that statistical methods have some strong advantages in practice.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142201/1/we2143-sup-0001-supplementary.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142201/2/we2143.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142201/3/we2143_am.pd
The influence of the starvation-predation trade-off on the relationship between ambient temperature and body size among endotherms
Aim: The tendency for animals at higher latitudes to be larger (Bergmann's rule) is generally explained by recourse to latitudinal effects on ambient temperature and the food supply, but these receive only mixed support and do not explain observations of the inverse to Bergmann's rule. Our aim was to better understand how ecological variables might influence body size and thereby explain this mixed support. Location: World-wide. Methods: Previous explanations do not allow for the selective pressure exerted by the trade-off between predation and starvation, which we incorporate in a model of optimal body size and energy storage of a generalized homeotherm. In contrast to existing arguments, we concentrate on survival over winter when the food supply is poor and can be interrupted for short periods. Results: We use our model to assess the logical validity of the heat conservation hypothesis and show that it must allow for the roles of both food availability and predation risk. We find that whether the effect of temperature on body size is positive or negative depends on temperature range, predator density, and the likelihood of long interruptions to foraging. Furthermore, changing day length explains differing effects of altitude and latitude on body size, leading to opposite predictions for nocturnal and diurnal endotherms. Food availability and ambient temperature can have counteracting selective pressures on body mass, and can lead to a non-monotonic relationship between latitude and size, as observed in several studies. Main conclusions: Our work provides a theoretical framework for understanding the relationships between the costs and benefits of large body size and eco-geographical patterns among endotherms world-wide
Kinematic dynamo action in a sphere: Effects of periodic time-dependent flows on solutions with axial dipole symmetry
Choosing a simple class of flows, with characteristics that may be present in
the Earth's core, we study the ability to generate a magnetic field when the
flow is permitted to oscillate periodically in time. The flow characteristics
are parameterised by D, representing a differential rotation, M, a meridional
circulation, and C, a component characterising convective rolls. Dynamo action
is sensitive to these flow parameters and fails spectacularly for much of the
parameter space where magnetic flux is concentrated into small regions.
Oscillations of the flow are introduced by varying the flow parameters in
time, defining a closed orbit in the space (D,M). Time-dependence appears to
smooth out flux concentrations, often enhancing dynamo action. Dynamo action
can be impaired, however, when flux concentrations of opposite signs occur
close together as smoothing destroys the flux by cancellation.
It is possible to produce geomagnetic-type reversals by making the orbit
stray into a region where the steady flows generate oscillatory fields. In this
case, however, dynamo action was not found to be enhanced by the
time-dependence.
A novel approach is taken to solving the time-dependent eigenvalue problem,
where by combining Floquet theory with a matrix-free Krylov-subspace method we
avoid large memory requirements for storing the matrix required by the standard
approach.Comment: 22 pages, 12 figures. Geophys. Astrophys. Fluid Dynam., as accepted
(2004
Visualizing the logistic map with a microcontroller
The logistic map is one of the simplest nonlinear dynamical systems that
clearly exhibit the route to chaos. In this paper, we explored the evolution of
the logistic map using an open-source microcontroller connected to an array of
light emitting diodes (LEDs). We divided the one-dimensional interval
into ten equal parts, and associated and LED to each segment. Every time an
iteration took place a corresponding LED turned on indicating the value
returned by the logistic map. By changing some initial conditions of the
system, we observed the transition from order to chaos exhibited by the map.Comment: LaTeX, 6 pages, 3 figures, 1 listin
Influence of information flow in the formation of economic cycles
A microscopic approach to macroeconomic features is intended. A model for
macroeconomic behavior based on the Ausloos-Clippe-Pekalski model is built and
investigated. The influence of a discrete time information transfer is
investigated. The formation of economic cycles is observed as a function of the
time of information delay. Three regions of delay time are recognized: short
(IS - iteration steps) - the system evolves toward a
unique stable equilibrium state, medium or , the
system undergoes oscillations: stable concentration cycles appear in the
system. For long information flow delay times, , the systems may
crash for most initial concentrations. However, even in the case of long delay
time the crash time may be long enough to allow observation of the system
evolution and to introduce an appropriate strategy in order to avoid the
collapse of the e.g. company concentration. In the long time delay it is also
possible to observe an "economy resonance" where despite a long delay time the
system evolves for a long time or can even reach a stable state, which insures
its existence.Comment: 18 pages,16 figures, to be published in Verhulst 200 Proceedings, M.
Ausloos and M. Dirickx, Eds. (in press
Genetic analyses of teacher ratings of problem behavior in 5-year-old twins
Behavioral problems in young children can be assessed by asking their parents or teachers to rate their behaviors. Genetic analyses of parental ratings show relatively large heritabilities for emotional and behavioral problems in young children, but data from teachers for this age group are scarce. Sources of variation in the Teacher's Report Form (TRF) problem scales were examined. The TRF was completed for 211 Dutch 5-year-old twin pairs and 4 single twins. Twins rated by different teachers had higher means and variances than twins rated by the same teacher, in addition twin correlations were lower in this group. In both groups monozygotic (MZ) correlations were generally higher than dizygotic (DZ) correlations. A model for twin resemblance was tested that allowed for these effects. For 5 problem scales (Withdrawn, Social Problems, Aggressive Behavior, Rule Breaking Behavior and Attention Problems) a model with genetic and unique environmental sources of variation fitted best to the data. For 3 problem scales (Anxious/Depressed, Thought Problems and Somatic Complaints) there were familial influences but it was not possible to distinguish between common environmental influences or genetic influences. Heritability was 63% for Attention problems, around 45% for Withdrawn, Social Problems, Aggressive Behavior and Rule Breaking Behavior, and around 30% for Anxious/Depressed, Thought Problems and Somatic Complaints
Ensemble averaged entanglement of two-particle states in Fock space
Recent results, extending the Schmidt decomposition theorem to wavefunctions
of identical particles, are reviewed. They are used to give a definition of
reduced density operators in the case of two identical particles. Next, a
method is discussed to calculate time averaged entanglement. It is applied to a
pair of identical electrons in an otherwise empty band of the Hubbard model,
and to a pair of bosons in the the Bose-Hubbard model with infinite range
hopping. The effect of degeneracy of the spectrum of the Hamiltonian on the
average entanglement is emphasised.Comment: 19 pages Latex, changed title, references added in the conclusion
Nodal points and the transition from ordered to chaotic Bohmian trajectories
We explore the transition from order to chaos for the Bohmian trajectories of
a simple quantum system corresponding to the superposition of three stationary
states in a 2D harmonic well with incommensurable frequencies. We study in
particular the role of nodal points in the transition to chaos. Our main
findings are: a) A proof of the existence of bounded domains in configuration
space which are devoid of nodal points, b) An analytical construction of formal
series representing regular orbits in the central domain as well as a numerical
investigation of its limits of applicability. c) A detailed exploration of the
phase-space structure near the nodal point. In this exploration we use an
adiabatic approximation and we draw the flow chart in a moving frame of
reference centered at the nodal point. We demonstrate the existence of a saddle
point (called X-point) in the vicinity of the nodal point which plays a key
role in the manifestation of exponential sensitivity of the orbits. One of the
invariant manifolds of the X-point continues as a spiral terminating at the
nodal point. We find cases of Hopf bifurcation at the nodal point and explore
the associated phase space structure of the nodal point - X-point complex. We
finally demonstrate the mechanism by which this complex generates chaos.
Numerical examples of this mechanism are given for particular chaotic orbits,
and a comparison is made with previous related works in the literature.Comment: 32 pages, 13 figures, Accepted for publication in Journal of Physics
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