220 research outputs found
Explaining variation in brood parasitism rates between potential host species with similar habitat requirements
Host specialization evolved in many parasite-host systems. Evolution and
maintenance of host specificity may be influenced by host life-history traits, active host
selection by the parasite, and host anti-parasite strategies. The relative importance of these
factors is poorly understood in situations that offer parasites a choice between hosts with
similar habitat requirements. The common cuckoo Cuculus canorus is a generalist parasite
on the species level, but individual females prefer particular host species. In reed beds of
the Yellow River Delta, China, two potential hosts with similar nest characteristics,
Oriental reed warblers Acrocephalus orientalis and reed parrotbills Paradoxornis heudei,
breed in sympatry. We found that warblers were parasitized at much higher rates than
parrotbills. Both hosts recognized and rejected non-mimetic model eggs well, indicating
that they have been involved in an arms-race with cuckoos. Cuckoo eggs closely resembled
warbler eggs, and such eggs were mostly accepted by warblers but rejected by parrotbills.
Only warblers recognized adult cuckoos as a specific threat. Both hosts were equally good
at raising cuckoo chicks. Low nest density, partial isolation by breeding time, small scale
differences in nest and nest site characteristics, and high rejection rates of natural cuckoo
eggs are likely cumulatively responsible for the low current parasitism rate in parrotbills.
This study emphasizes the importance of integrating the study of general host life-history
characteristics and specific anti-parasitism strategies of hosts across all breeding stages to
understand the evolution of host specificity.submittedVersionpublishedVersio
Size dependent thermoelectric properties of silicon nanowires
By using first-principles tight-binding electronic structure calculation and
Boltzmann transport equation, we investigate the size dependence of
thermoelectric properties of silicon nanowires (SiNWs). With cross section area
increasing, the electrical conductivity increases slowly, while the Seebeck
coefficient reduces remarkably. This leads to a quick reduction of cooling
power factor with diameter. Moreover, the figure of merit also decreases with
transverse size. Our results demonstrate that in thermoelectric application, NW
with small diameter is preferred. We also predict that isotopic doping can
increase the value of ZT significantly. With 50% 29Si doping (28Si0.529Si0.5
NW), the ZT can be increased by 31%.Comment: 13 pages, 4 figure
Uncrewed Ocean Gliders and Saildrones Support Hurricane Forecasting and Research
In the United States alone, hurricanes have been responsible for thousands of deaths and over US$1 trillion in damages since 1980 (https://www.ncdc.noaa.gov/billions/). These impacts are significantly greater globally, particularly in regions with limited hurricane early warning systems and where large portions of the population live at or near sea level. The high socioeconomic impacts of tropical cyclones will increase with a changing climate, rising sea level, and increasing coastal populations. To mitigate these impacts, efforts are underway to improve hurricane track and intensity forecasts, which drive storm surge models and evacuation orders and guide coastal preparations. Hurricane track forecasts have improved steadily over past decades, whileintensity forecasts have lagged until recently (Cangialosi et al., 2020). Hurricane intensity changes are influenced by a combination of large-scale atmospheric circulation, internal storm dynamics, and air-sea interactions (Wadler et al.,2021, and references therein)
Surface structure and multigap superconductivity of V3Si (111) revealed by scanning tunneling microscopy
V3Si, a classical silicide superconductor with relatively high TC (~16 K), is
promising for constructing silicon-based superconducting devices and
hetero-structures. However, real space characterization on its surfaces and
superconducting properties are still limited. Here we report the first
low-temperature scanning tunnelling microscopy (STM) study on cleaned V3Si
(111) single crystal surface. We observed a r3 by r3 superstructure which
displays mirror symmetry between adjacent terraces, indicating the surface is
V-terminated and reconstructed. The tunneling spectrum shows full
superconducting gap with double pairs of coherence peaks, but has a relatively
small gap size with comparing to bulk TC. Impurity induced in-gap state is
absent on surface defects but present on introduced magnetic adatoms. Upon
applying magnetic field, a hexagonal vortex lattice is visualized.
Interestingly, the vortex size is found to be field dependent, and the
coherence length measured from single vortex at low field is significantly
larger than estimated value from bulk H_c2. These results reflect V3Si is a
multi-band, s- wave superconductor
Nonlinear Landau resonant interaction between whistler waves and electrons: Excitation of electron acoustic waves
Electron acoustic waves (EAWs), as well as electron-acoustic solitary
structures, play a crucial role in thermalization and acceleration of electron
populations in Earth's magnetosphere. These waves are often observed in
association with whistler-mode waves, but the detailed mechanism of EAW and
whistler wave coupling is not yet revealed. We investigate the excitation
mechanism of EAWs and their potential relation to whistler waves using
particle-in-cell simulations. Whistler waves are first excited by electrons
with a temperature anisotropy perpendicular to the background magnetic field.
Electrons trapped by these whistler waves through nonlinear Landau resonance
form localized field-aligned beams, which subsequently excite EAWs. By
comparing the growth rate of EAWs and the phase mixing rate of trapped electron
beams, we obtain the critical condition for EAW excitation, which is consistent
with our simulation results across a wide region in parameter space. These
results are expected to be useful in the interpretation of concurrent
observations of whistler-mode waves and nonlinear solitary structures, and may
also have important implications for investigation of cross-scale energy
transfer in the near-Earth space environment
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