5,808 research outputs found
Optimal traps in graphene
We transform the two-dimensional Dirac-Weyl equation, which governs the
charge carriers in graphene, into a non-linear first-order differential
equation for scattering phase shift, using the so-called variable phase method.
This allows us to utilize the Levinson Theorem to find zero-energy bound states
created electrostatically in realistic structures. These confined states are
formed at critical potential strengths, which leads to us posit the use of
`optimal traps' to combat the chiral tunneling found in graphene, which could
be explored experimentally with an artificial network of point charges held
above the graphene layer. We also discuss scattering on these states and find
the zero angular momentum states create a dominant peak in scattering
cross-section as energy tends towards the Dirac point energy, suggesting a
dominant contribution to resistivity.Comment: 11 pages, 5 figure
Geometric, aerodynamic, and kinematic characteristics of two twin keel parawings during deployment
Flight test data on geometric, aerodynamic, and kinematic characteristics of two twin keel parawings during deploymen
Photoionization and Photoelectric Loading of Barium Ion Traps
Simple and effective techniques for loading barium ions into linear Paul
traps are demonstrated. Two-step photoionization of neutral barium is achieved
using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by
excitation above the ionization threshold using a nitrogen gas laser (337 nm).
Isotopic selectivity is achieved by using a near Doppler-free geometry for
excitation of the triplet 6s6p 3P1 state. Additionally, we report a
particularly simple and efficient trap loading technique that employs an
in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3
caption -added reference [15
Quenched Cold Accretion of a Large Scale Metal-Poor Filament due to Virial Shocking in the Halo of a Massive z=0.7 Galaxy
Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a
remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI
absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile
components, and resides at an impact parameter of D=58 kpc from a bright, high
mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6
Gyr old, solar metallicity stellar population. Ionization models suggest the
majority of the structure is cold gas surrounding a shock heated cloud that is
kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV
and OVI absorption, suggestive of a conductive interface near the shock. The
deduced metallicities are consistent with the moderate in situ enrichment
relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the
HI complex as a metal-poor filamentary structure being shock heated as it
accretes into the halo of the galaxy. The data support the scenario of an early
formation period (z > 4) in which the galaxy was presumably fed by cold-mode
gas accretion that was later quenched via virial shocking by the hot halo such
that, by intermediate redshift, the cold filamentary accreting gas is
continuing to be disrupted by shock heating. Thus, continued filamentary
accretion is being mixed into the hot halo, indicating that the star formation
of the galaxy will likely remain quenched. To date, the galaxy and the HI
absorption complex provide some of the most compelling observational data
supporting the theoretical picture in which accretion is virial shocked in the
hot coronal halos of high mass galaxies.Comment: 20 pages, 9 figures, submitted to Ap
Afterslip Moment Scaling and Variability from a Global Compilation of Estimates
Aseismic afterslip is postseismic fault sliding that may significantly redistribute crustal stresses and drive aftershock sequences. Afterslip is typically modeled through geodetic observations of surface deformation on a case-by-case basis, thus questions of how and why the afterslip moment varies between earthquakes remain largely unaddressed. We compile 148 afterslip studies following 53 Mw6.0–9.1 earthquakes, and formally analyze a subset of 88 well-constrained kinematic models. Afterslip and coseismic moments scale near-linearly, with a median Spearman's rank correlation coefficient (CC) of 0.91 after bootstrapping (95% range: 0.89–0.93). We infer that afterslip area and average slip scale with coseismic moment as urn:x-wiley:21699313:media:jgrb55593:jgrb55593-math-0001 and urn:x-wiley:21699313:media:jgrb55593:jgrb55593-math-0002, respectively. The ratio of afterslip to coseismic moment (Mrel) varies from 300% (interquartile range: 9%–32%). Mrel weakly correlates with Mo (CC: −0.21, attributed to a publication bias), rupture aspect ratio (CC: −0.31), and fault slip rate (CC: 0.26, treated as a proxy for fault maturity), indicating that these factors affect afterslip. Mrel does not correlate with mainshock dip, rake, or depth. Given the power-law decay of afterslip, we expected studies that started earlier and spanned longer timescales to capture more afterslip, but Mrel does not correlate with observation start time or duration. Because Mrel estimates for a single earthquake can vary by an order of magnitude, we propose that modeling uncertainty currently presents a challenge for systematic afterslip analysis. Standardizing modeling practices may improve model comparability, and eventually allow for predictive afterslip models that account for mainshock and fault zone factors to be incorporated into aftershock hazard models
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