1,199,014 research outputs found
New electron microscope employs new video display technique
Video display system for a scanning electron microscope provides slow scanning rates, a self-generated color gradient technique, and allows leisurely viewing of several hours. It also enables the viewing of areas where selected energy regions contribute relatively few electrons, and the changing of specimen position and magnification without adjustments
Modeling the effects of wind tunnel wall absorption on the acoustic radiation characteristics of propellers
Finite element theory is used to calculate the acoustic field of a propeller in a soft walled circular wind tunnel and to compare the radiation patterns to the same propeller in free space. Parametric solutions are present for a "Gutin" propeller for a variety of flow Mach numbers, admittance values at the wall, microphone position locations, and propeller to duct radius ratios. Wind tunnel boundary layer is not included in this analysis. For wall admittance nearly equal to the characteristic value of free space, the free field and ducted propeller models agree in pressure level and directionality. In addition, the need for experimentally mapping the acoustic field is discussed
Dispersion and transitions of dipolar plasmon modes in graded plasmonic waveguides
Coupled plasmon modes are studied in graded plasmonic waveguides, which are
periodic chains of metallic nanoparticles embedded in a host with gradually
varying refractive indices. We identify three types of localized modes called
"light", "heavy", and "light-heavy" plasmonic gradons outside the passband,
according to various degrees of localization. We also demonstrate new
transitions among extended and localized modes when the interparticle
separation is smaller than a critical , whereas the three types of
localized modes occur for , with no extended modes. The transitions can
be explained with phase diagrams constructed for the lossless metallic systems.Comment: Preliminary results have been presented at ETOPIM 7. Submitted to
Appl. Phys. Let
Charge Disproportionation and Spin Ordering Tendencies in Na(x)CoO2
The strength and effect of Coulomb correlations in the (superconducting when
hydrated) x~1/3 and ``enhanced'' x~2/3 regimes of Na(x)CoO2 are evaluated using
the correlated band theory LDA+U method. Our results, neglecting quantum
fluctuations, are: (1) allowing only ferromagnetic order, there is a critical
U_c = 3 eV, above which charge disproportionation occurs for both x=1/3 and
x=2/3, (2) allowing antiferromagnetic order at x=1/3, U_c drops to 1 eV for
disproportionation, (3) disproportionation and gap opening occur
simultaneously, (4) in a Co(3+)-Co(4+) ordered state, antiferromagnetic
coupling is favored over ferromagnetic, while below U_c ferromagnetism is
favored. Comparison of the calculated Fermi level density of states compared to
reported linear specific heat coefficients indicates enhancement of the order
of five for x~0.7, but negligible enhancement for x~0.3. This trend is
consistent with strong magnetic behavior and local moments (Curie-Weiss
susceptibility) for x>0.5 while there no magnetic behavior or local moments
reported for x<0.5. We suggest that the phase diagram is characterized by a
crossover from effective single-band character with U >> W for x>0.5 into a
three-band regime for x U_eff <= U/\sqrt(3) ~ W and
correlation effects are substantially reduced.Comment: 10 pages, 8 figures, corrected a few typos and changed reference
Radiative penguin Bs decays at Belle
We report searches for the radiative penguin decays Bs to phi gamma and Bs to
gamma gamma based on a 23.6 fb-1 data sample collected with the Belle detector
at the KEKB e+e- energy-asymmetric collider operating at the Upsilon(5S)
resonance.Comment: On behalf of the Belle Collaboration. To appear in the proceedings of
the International Europhysics Conference on High Energy Physics
(EPS-HEP2007), Manchester, England, 19-25 July 2007. 3 pages, 2 figure
COPTRAN - A method of optimum communication systems design
Single set of mathematical expressions describes system cost and probability of error of data transmission in terms of four basic parameters in the link equation. A Lagrange multiplier sets up equations whose solutions yield the optimum values for system design considerations and weight and cost values
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