8,752 research outputs found
Susceptibility of White Spruce Seed Sources to Yellowheaded Spruce Sawfly, \u3ci\u3ePikonema Alaskensis,\u3c/i\u3e(Hymenoptera: Tenthredinidae)
A field caging technique was used to test the susceptibility of 25 white spruce, Picea glauca (Moench) Voss, seed sources to attack by Pikonema alaskensis (Rohwer). No sig- nificant differences were found in the number of eggs laid, number of dessicated eggs, or number of egg slits. Percent oviposition differed significantly within a tree, the south side having more eggs. Bud size differed significantly within trees and between trees but not between seed sources. The number of sawfly eggs laid on a bud could not be related to bud size. There was no significant difference in susceptibility of the seed sources studied to Pikonema alaskensis
Head-on collision of ultrarelativistic charges
We consider the head-on collision of two opposite-charged point particles
moving at the speed of light. Starting from the field of a single charge we
derive in a first step the field generated by uniformly accelerated charge in
the limit of infinite acceleration. From this we then calculate explicitly the
burst of radiation emitted from the head-on collision of two charges and
discuss its distributional structure. The motivation for our investigation
comes from the corresponding gravitational situation where the head-on
collision of two ultrarelativistic particles (black holes) has recently aroused
renewed interest.Comment: 4 figures, uses the AMSmat
Bostonia. Volume 6
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Mid-Infrared Ethane Emission on Neptune and Uranus
We report 8- to 13-micron spectral observations of Neptune and Uranus from
the NASA Infrared Telescope Facility spanning more than a decade. The
spectroscopic data indicate a steady increase in Neptune's mean atmospheric
12-micron ethane emission from 1985 to 2003, followed by a slight decrease in
2004. The simplest explanation for the intensity variation is an increase in
stratospheric effective temperature from 155 +/- 3 K in 1985 to 176 +/- 3 K in
2003 (an average rate of 1.2 K/year), and subsequent decrease to 165 +/- 3 K in
2004. We also detected variation of the overall spectral structure of the
ethane band, specifically an apparent absorption structure in the central
portion of the band; this structure arises from coarse spectral sampling
coupled with a non-uniform response function within the detector elements. We
also report a probable direct detection of ethane emission on Uranus. The
deduced peak mole fraction is approximately an order of magnitude higher than
previous upper limits for Uranus. The model fit suggests an effective
temperature of 114 +/- 3 K for the globally-averaged stratosphere of Uranus,
which is consistent with recent measurements indicative of seasonal variation.Comment: Accepted for publication in ApJ. 16 pages, 10 figures, 2 table
Relative age effects on academic achievement in the first ten years of formal schooling: A nationally representative longitudinal prospective study
The effects of school starting age and relative age effects (RAEs) have generated much interest from parents, teachers, policymakers, and educational researchers. Our 10-year longitudinal study is based on a nationally representative (N = 4,983) prospective sample from the Longitudinal Study of Australian Children. The primary outcomes are results from the high-stake, Australia-wide National Assessment Program-Literacy and Numeracy tests in Years 3, 5, 7, and 9, controlling for demographic characteristics (gender, socioeconomic status, school type, and childhood cognition measured before the start of kindergarten). We evaluated how direct and mediated RAEs vary over the first 10 years of schooling for these longitudinal data. Results revealed significant RAEs in primary school years for both numeracy and literacy test outcomes. Effects were large in primary school years but declined in secondary school years. Although the direct effects of RAEs declined over time, there continued to be significant indirect effects over the whole 10-year period. RAEs in primary school had enduring effects that were mediated through the effects of earlier achievement. We juxtapose our results with previous RAE research on achievement and a range of other noncognitive outcomes where the RAEs are enduring into adolescence and even adulthood. We position our research within this broader research literature and discuss implications for educational policy, practice, theory, and future research
Radiative damping: a case study
We are interested in the motion of a classical charge coupled to the Maxwell
self-field and subject to a uniform external magnetic field, B. This is a
physically relevant, but difficult dynamical problem, to which contributions
range over more than one hundred years. Specifically, we will study the
Sommerfeld-Page approximation which assumes an extended charge distribution at
small velocities. The memory equation is then linear and many details become
available. We discuss how the friction equation arises in the limit of "small"
B and contrast this result with the standard Taylor expansion resulting in a
second order equation for the velocity of the charge.Comment: 4 figure
Insulator-Metal Transition in the One and Two-Dimensional Hubbard Models
We use Quantum Monte Carlo methods to determine Green functions,
, on lattices up to for the 2D Hubbard model
at . For chemical potentials, , within the Hubbard gap, , and at {\it long} distances, , with critical behavior: , . This result stands in agreement with the
assumption of hyperscaling with correlation exponent and dynamical
exponent . In contrast, the generic band insulator as well as the
metal-insulator transition in the 1D Hubbard model are characterized by and .Comment: 9 pages (latex) and 5 postscript figures. Submitted for publication
in Phys. Rev. Let
Approximate quantum cloning and the impossibility of superluminal information transfer
We show that nonlocality of quantum mechanics cannot lead to superluminal
transmission of information, even if most general local operations are allowed,
as long as they are linear and trace preserving. In particular, any quantum
mechanical approximate cloning transformation does not allow signalling. On the
other hand, the no-signalling constraint on its own is not sufficient to
prevent a transformation from surpassing the known cloning bounds. We
illustrate these concepts on the basis of some examples.Comment: 4 pages, 1eps figur
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