We give results for the Upsilon spectrum from lattice QCD using an improved version of the NRQCD action for b quarks which includes radiative corrections to kinetic terms at O(v 4 ) in the velocity expansion. We also include for the first time the effect of up, down, strange and charm quarks in the sea using 'second generation' gluon field configurations from the MILC collaboration. Using the Υ 2S − 1S splitting to determine the lattice spacing, we are able to obtain the 1P − 1S splitting to 1.4% and the 3S − 1S splitting to 2.4%. Our improved result for M (Υ) − M (η b ) is 70(9) MeV and we predict M (Υ ) − M (η b ) = 35(3) MeV. We also calculate π, K and ηs correlators using the Highly Improved Staggered Quark action and perform a chiral and continuum extrapolation to give values for Mη s (0.6893(12) GeV) and fη s (0.1819(5) GeV) that allow us to tune the strange quark mass as well as providing an independent and consistent determination of the lattice spacing. Combining the NRQCD and HISQ analyses gives m b /ms = 54.7(2.5) and a value for the heavy quark potential parameter of r1 = 0.3209(26) fm.

The time‐of‐flight method has been used to study the effect of P3HT molecular weight (Mn = 13–121 kDa) on charge mobility in pristine and PCBM blend films using highly regioregular P3HT. Hole mobility was observed to remain constant at 10−4 cm2V−1s−1 as molecular weight was increased from 13–18 kDa, but then decreased by one order of magnitude as molecular weight was further increased from 34–121 kDa. The decrease in charge mobility observed in blend films is accompanied by a change in surface morphology, and leads to a decrease in the performance of photovoltaic devices made from these blend films.

Transient photovoltage and differential charging have been used to measure the charge density and recombination rate in polymer solar cells consisting of regioregular poly(3-hexythiophene) (P3HT) blended with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methano fullerene (PCBM). Charge dynamics were found to be over an order of magnitude faster in nonannealed cells as compared to annealed cells. Numerical modeling demonstrated that physically reasonable changes in the domain size and phase segregation reproduced the change seen in the experimental results and thus suggests that measurements of recombination rate can be used as an indicator of the degree of intermixing of donor and acceptor in bulk heterojunction solar cells. Through calculation of the recombination flux at both open circuit and short circuit conditions, we determine that the increase in rate constant observed for the nonannealed devices is sufficient to explain the differences in device performance.

We present improved results for the B and D meson spectrum from lattice QCD including the effect of u=d, s and c quarks in the sea. For the B mesons the highly improved staggered quark action is used for the sea and light valence quarks and nonrelativistic QCD for the b quark including Oð s Þ radiative corrections to many of the Wilson coefficients for the first time. The D mesons use the highly improved staggered quark action for both valence quarks on the same sea. We find M B s À M B ¼ 84ð2Þ MeV, M B s ¼ 5:366ð8Þ GeV, M B c ¼ 6:278ð9Þ GeV, M D s ¼ 1:9697ð33Þ GeV, and M D s À M D ¼ 101ð3Þ MeV. Our results for the B meson hyperfine splittings are M B Ã À M B ¼ 50ð3Þ MeV, M B Ã s À M B s ¼ 52ð3Þ MeV, in good agreement with existing experimental results. This demonstrates that our perturbative improvement of the nonrelativistic QCD chromomagnetic coupling works for both heavyonium and heavylight mesons. We predict M B Ã c À M B c ¼ 54ð3Þ MeV. We also present first results for the radially excited B c states as well as the orbitally excited scalar B Ã c0 and axial-vector B c1 mesons.

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