Plasmon dispersion in semimetallic armchair graphene nanoribbons

The dispersion relations for plasmons in intrinsic and extrinsic semimetallic armchair graphene nanoribbons (acGNR) are calculated in the random phase approximation using the orthogonal p_z-orbital tight binding method. Our model predicts new plasmons for acGNR of odd atomic widths N=5,11,17,... Our model further predicts plasmons in acGNR of even atomic width N=2,8,14,... related to those found using a Dirac continuum model, but with different quantitative dispersion characteristics. We find that the dispersion of all plasmons in semimetallic acGNR depends strongly on the localization of the p_z electronic wavefunctions. We also find that overlap integrals for acGNR behave in a more complex way than predicted by the Dirac continuum model, suggesting that these plasmons will experience a small damping for all q not equal to 0. Plasmons in extrinsic semimetallic acGNR with the chemical potential in the lowest (highest) conduction (valence) band are found to have dispersion characteristics nearly identical to their intrinsic counterparts, with negligible differencs in dispersion arising from the slight differences in overlap integrals for the interband and intraband transitions.Comment: 8 pages, 9 figure

The Intrinsic Ellipticity of Spiral Disks

We have measured the distribution of intrinsic ellipticities for a sample of 28 relatively face-on spiral disks. We combine H-alpha velocity fields and R and I-band images to determine differences between kinematic and photometric inclination and position angles, from which we estimate intrinsic ellipticities of galaxy disks. Our findings suggest disks have a log-normal distribution of ellipticities (mean epsilon =0.06) and span a range from epsilon= 0 (circular) to epsilon=0.2. We are also able to construct a tight Tully-Fisher relation for our face-on sample. We use this to assess the contribution of disk ellipticity on the observed Tully-Fisher scatter.Comment: 4 pages, 2 figures, to appear in "Disks of Galaxies: Kinematics, Dynamics and Perturbations" (ASP Conference Series), eds E.Athanassoula and A. Bosm

A Face-On Tully-Fisher Relation

We construct the first "face-on" Tully-Fisher (TF) relation for 24 galaxies with inclinations between 16 degrees and 41 degrees. The enabling measurements are integral-field, echelle spectroscopy from the WIYN 3.5m telescope, which yield accurate kinematic estimates of disk inclination to 15 degrees. Kinematic inclinations are of sufficient accuracy that our measured TF scatter of 0.42 mag is comparable to other surveys even without internal-absorption corrections. Three of four galaxies with significant kinematic and photometric asymmetries also have the largest deviations from our TF relation, suggesting that asymmetries make an important contribution to TF scatter. By measuring inclinations below 40 degrees, we establish a direct path to linking this scatter to the unprojected structure of disks and making non-degenerate dynamical mass-decompositions of spiral galaxies.Comment: 13 pages, 3 figures (2 color). Accepted for publication in ApJ Letter

Tarnishing Silver Bullets: Bt Technology Adoption, Bounded Rationality and the Outbreak of Secondary Pest Infestations in China

As with other technologies, adoption of Bt seed requires technology specific knowledge. Growing secondary pest populations have slowly eroded the benefits of Bt technology in China. We illustrate the effects of introducing Bt technology among farmers with an imperfect knowledge of secondary pest problems using a simple dynamic model. The stochastic dominance tests based on primary household data from 1999-2001 and 2004 in China provide strong evidence that secondary pests, if unanticipated, could completely erode all benefits from Bt cotton cultivation. Our empirical tests also suggest that planting refuge concurrent with Bt adoption provides for the sustainable development of Bt technology.Research and Development/Tech Change/Emerging Technologies,

Getting on the Agenda: The Influence of Local Civil Society Organizations during Pre-Negotiation

This article examines the types of strategies that different local civil society organizations use to get their issues addressed during a peace negotiation. Previous research has shown that the inclusion of civil society groups in a negotiation improves the likelihood for a durable peace. This paper argues that during conflict civil society organizations make a number of strategic choices that then affect their ability to get their societal interests placed on the agenda. These strategies are partially dictated by when and why the civil society group organized, the levels and types of advocacy that they choose to engage in during the conflict, and whether they were able to continue to advocate within the conflict zone. This framework represents a preliminary investigation for developing a deeper understanding of these processes

CALL BROADCASTING AND AUTOMATED RECORDERS AS TOOLS FOR ANURAN SURVEYS IN A SUBARCTIC TUNDRA LANDSCAPE

Relatively little is known about population ecology of anurans in arctic and subarctic tundra regions, in part because it is difficult to survey anurans in these landscapes. Anuran survey protocols developed for temperate regions have limited applicability in arctic and subarctic tundra landscapes, which may lack roads and vehicle access, and experience variable and inclement weather during short anuran breeding seasons. To evaluate approaches to address some of the limitations of surveying anurans in tundra landscapes, we assessed the effectiveness of using breeding call broadcasts to increase detection of Boreal Chorus Frogs (Pseudacris maculata) and Wood Frogs (Lithobates sylvaticus) near Cape Churchill, Manitoba, Canada. We also evaluated how counts of anurans derived from automated audio recorders compared with those obtained simultaneously by observers. We detected on average 0.4 additional Wood Frogs per survey when we broadcasted calls (x = 0.82, SD = 1.38), an increase of > 40% compared to surveys without broadcasts (x = 1.24, SD = 1.51; Wilcoxon test; Z = 2.73, P = 0.006). In contrast, broadcasting Boreal Chorus Frog calls did not increase the number of chorus frog detections (Wilcoxon test; Z < 0.001, P > 0.90). Detections of Wood Frogs in a 100-m radius were lower via automated recorders (x = 0.60, SD = 0.87 SD) than by observers during simultaneous surveys (x = 0.96, SD = 1.27 Z = 2.07, P = 0.038), but those of Boreal Chorus Frogs were not different (x = 1.72, SD = 1.31;x = 1.44, SD = 1.5; Z = 1.55, P > 0.121). Our results suggest that broadcasting calls can increase detection of Wood Frogs, and that automated recorders are useful in detecting both Wood Frogs and Boreal Chorus Fogs in arctic and subarctic tundra landscapes