7,260 research outputs found
Comparisons between the squash bug egg parasitoids Ooencyrtus anasae and O. sp. (Hymenoptera: Encyrtidae): development, survival,and sex ratio in relation to temperature
Citation: Tracy, J. L., and J. R. Nechols. 1987. “Comparisons Between the Squash Bug Egg Parasitoids Ooencyrtus Anasae and O. Sp. (Hymenoptera: Encyrtidae): Development, Survival, and Sex Ratio in Relation to Temperature.” Environmental Entomology 16 (6): 1324–29. https://doi.org/10.1093/ee/16.6.1324.Laboratory investigations of the gregarious squash bug egg parasitoids Ooencyrtus anasae and O. n. sp. near anasae (O. sp.) were conducted at 20.8, 23.0, and 26.6°C. In both species, total developmental periods (egg to eclosed adult) were inversely related to temperature. Temperature had no significant influence on survivorship, progeny production, or sex ratio. At each temperature, O. anasae developed and emerged about a day earlier and produced a significantly higher percentage of female progeny (77%) than did O. sp. (60%). Both parasitoids deposited an average of three (2-7) progeny per host. However, O. anasae consistently deposited more female eggs per host than did O. sp. Proportion of females produced per host by O. anasae tended to increase directly with number of hosts parasitized, but no such relationship was observed in O. sp. Total preimaginal survivorship in both parasitoids was about 89%. In O. sp., male progeny that developed without females emerged about a day later at all temperatures and had a lower pharate adult survivorship than did males that developed in hosts with female siblings
Resistively-Detected NMR in a Two-Dimensional Electron System near : Clues to the Origin of the Dispersive Lineshape
Resistively-detected NMR measurements on 2D electron systems near the quantum Hall state are reported. In contrast to recent results of Gervais
\emph{et al.} [Phys. Rev. Lett. , 196803 (2005)], a dispersive
lineshape is found at all RF powers studied and Korringa-like nuclear
spin-lattice relaxation is observed. The shape of the unexplained dispersive
lineshape is found to invert when the temperature derivative of the
longitudinal resistance changes sign. This suggests that both Zeeman and
thermal effects are important to resistively-detected NMR in this regime.Comment: 5 pages, 4 figures. Version accepted for publication in Phys. Rev.B,
Rapid Communication
Spin Transition in the Half-Filled Landau Level
The transition from partial to complete spin polarization of two-dimensional
electrons at half filling of the lowest Landau level has been studied using
resistively-detected nuclear magnetic resonance (RDNMR). The nuclear
spin-lattice relaxation time is observed to be density independent in the
partially polarized phase but to increase sharply at the transition to full
polarization. At low temperatures the RDNMR signal exhibits a strong maximum
near the critical density.Comment: 4 pages, 3 postscript figures. As published in Phys. Rev. Lett. 98,
086801 (2007
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Using Additives to Control the Decomposition Temperature of Sodium Borohydride
Finite time corrections in KPZ growth models
We consider some models in the Kardar-Parisi-Zhang universality class, namely
the polynuclear growth model and the totally/partially asymmetric simple
exclusion process. For these models, in the limit of large time t, universality
of fluctuations has been previously obtained. In this paper we consider the
convergence to the limiting distributions and determine the (non-universal)
first order corrections, which turn out to be a non-random shift of order
t^{-1/3} (of order 1 in microscopic units). Subtracting this deterministic
correction, the convergence is then of order t^{-2/3}. We also determine the
strength of asymmetry in the exclusion process for which the shift is zero.
Finally, we discuss to what extend the discreteness of the model has an effect
on the fitting functions.Comment: 34 pages, 5 figures, LaTeX; Improved version including shift of PASEP
height functio
Surface Acoustic Wave Propagation and Inhomogeneities in Low Density Two-Dimensional Electron Systems Near the Metal-Insulator Transition
We have measured the surface acoustic wave velocity shift in a GaAs/AlGaAs
heterostructure containing a two-dimensional electron system (2DES) in a
low-density regime ( cm) at zero magnetic field. The
interaction of the surface acoustic wave with the 2DES is not well described by
a simple model using low-frequency conductivity measurements. We speculate that
this conflict is a result of inhomogeneities in the 2DES which become very
important at low density. This has implications for the putative
metal-insulator transition in two dimensions.Comment: 5 pages, 5 figure
Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF_3
Cubic scandium trifluoride (ScF_3) has a large negative thermal expansion over a wide range of temperatures. Inelastic neutron scattering experiments were performed to study the temperature dependence of the lattice dynamics of ScF3 from 7 to 750 K. The measured phonon densities of states show a large anharmonic contribution with a thermal stiffening of modes around 25 meV. Phonon calculations with first-principles methods identified the individual modes in the densities of states, and frozen phonon calculations showed that some of the modes with motions of F atoms transverse to their bond direction behave as quantum quartic oscillators. The quartic potential originates from harmonic interatomic forces in the DO_9 structure of ScF_3, and accounts for phonon stiffening with the temperature and a significant part of the negative thermal expansion
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