4,536 research outputs found
Measuring and modelling optical scattering and the colour quality of white pierid butterfly scales
Copyright © 2009 Optical Society of America. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-17-14729 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Colouration in butterfly wings is due to the interaction of light with a covering of scales on both wing surfaces. A combination of nanostructure in the scales, which reflect or scatter light, and absorption from chemical pigments in the scales and wing substrate create the final colour appearance. We compared the wing scale morphology of the pierid butterfly Pieris rapae (Small White) to the reflectance spectra from its wings. Its wing scales contain a dense array of pterin pigment beads. A positive correlation between bead-array density and wing reflectance, at wavelengths where the pigment does not absorb, was identified and characterised. We observed, however, that light scatter from these beads does not account for all of the broadband light scatter observed from the wings. The rest of the scale structure plays an important role in achieving high light scatter. Furthermore, combining the underlying scattering and absorption mechanisms within the butterfly scales enabled us to quantify the optical characteristics of the samples using CIELab colour theory
Neutron Scattering Study of URuReSi with = 0.10: Driving Order towards Quantum Criticality
We report inelastic neutron scattering measurements in the hidden order state
of URuReSi with = 0.10. We observe that towards the
ferromagnetic quantum critical point induced by the negative chemical pressure
of Re-doping, the gapped incommensurate fluctuations are robust and comparable
in intensity to the parent material. As the Re doping moves the system toward
the quantum critical point, the commensurate spin fluctuations related to
hidden order weaken, display a shortened lifetime and slow down. Halfway to the
quantum critical point, the hidden order phase survives, albeit weakened, in
contrast to its destruction by hydrostatic pressure and by positive chemical
pressure from Rh-doping.Comment: 5 pages, 6 figures, 24 reference
Renormalization group scaling in nonrelativistic QCD
We discuss the matching conditions and renormalization group evolution of
non-relativistic QCD. A variant of the conventional MS-bar scheme is proposed
in which a subtraction velocity nu is used rather than a subtraction scale mu.
We derive a novel renormalization group equation in velocity space which can be
used to sum logarithms of v in the effective theory. We apply our method to
several examples. In particular we show that our formulation correctly
reproduces the two-loop anomalous dimension of the heavy quark production
current near threshold.Comment: (27 pages, revtex
Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut
We compute the first two moments of the final hadronic invariant mass in
inclusive semileptonic B decay, in the presence of a cut on the charged lepton
energy. These moments may be measured directly by experiments at the
Upsilon(4S) using the neutrino reconstruction technique, which requires such a
cut. Measurement of these moments will place constraints on the nonperturbative
parameters \bar\Lambda and \lambda_1, which are relevant for extracting the
quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of
order \alpha_s^2\beta_0 and 1/m_b^3 in the operator product expansion, and use
the latter to estimate the theoretical uncertainty in the extraction of
\bar\Lambda and \lambda_1.Comment: 13 pages, 5 figures, REVTe
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