Density in a Planetary Exosphere

A discussion of the Opik-Singer theory of the density of a planetary exosphere is presented. Their density formula permits the calculation of the depth of the exosphere. Since the correctness of their derivation of the basic formula for the density distribution has been questioned, an alternate method based directly on Liouville's theorem is given. It is concluded that the Opik-Singer formula seems valid for the ballistic component of the exosphere; but for a complete description of the planetary exosphere, the ionized and bound-orbit components must also be included

Screen for DNA-damage-responsive histone modifications identifies H3K9Ac and H3K56Ac in human cells

Recognition and repair of damaged DNA occurs within the context of chromatin. The key protein components of chromatin are histones, whose post-translational modifications control diverse chromatin functions. Here, we report our findings from a large-scale screen for DNA-damage-responsive histone modifications in human cells. We have identified specific phosphorylations and acetylations on histone H3 that decrease in response to DNA damage. Significantly, we find that DNA-damage-induced changes in H3S10p, H3S28p and H3.3S31p are a consequence of cell-cycle re-positioning rather than DNA damage per se. In contrast, H3K9Ac and H3K56Ac, a mark previously uncharacterized in human cells, are rapidly and reversibly reduced in response to DNA damage. Finally, we show that the histone acetyl-transferase GCN5/KAT2A acetylates H3K56 in vitro and in vivo. Collectively, our data indicate that though most histone modifications do not change appreciably after genotoxic stress, H3K9Ac and H3K56Ac are reduced in response to DNA damage in human cells

Evaluation of Jobsite Cylinder Curing Practices for the Alabama Concrete Industry

The effect of initial curing temperature and duration on the 28-day compressive strength of concrete was experimentally evaluated. Concrete cylinders were cured at six initial curing temperatures (60, 68, 78, 84, 90, and 100 \u2070F) for three different initial curing durations (24, 48, and 72 hours). After the initial curing duration was complete, the cylinders were moved to final curing in a moist cure room that maintained a temperature of 73.5 \ub1 3.5 \ub0F until compressive strength testing at 28 days. Eight different concretes were produced at elevated temperatures to simulate summer placement conditions. The results confirm that as the initial curing temperature increases, the 28-day concrete compressive strength decreases. When cured at an initial curing temperature of 100 \u2070F, a maximum reduction of 23% in the 28-day compressive strength occurred. It is critical to maintain initial curing temperatures ranging from 60 to 80 \u2070F because then the change in 28-day strength remains within the acceptable ranges. When the initial curing temperature ranges from 60 to 80 \u2070F, then increasing the initial curing duration from 48 hour to 72 hour does not significantly affect the 28-day concrete compressive strength. The maximum initial curing duration can thus be increased from 48 to 72 hours, which will permit cylinders made on Fridays to be transported to their final curing location on Mondays

Erratum: Sequence data and association statistics from 12,940 type 2 diabetes cases and controls.

This corrects the article DOI: 10.1038/sdata.2017.179

Single-spin Azimuthal Asymmetries in Electroproduction of Neutral Pions in Semi-inclusive Deep-inelastic Scattering

A single-spin asymmetry in the azimuthal distribution of neutral pions relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. The analysing power in the sin(phi) moment of the cross section is 0.019 +/- 0.007(stat.) +/- 0.003(syst.). This result is compared to single-spin asymmetries for charged pion production measured in the same kinematic range. The pi^0 asymmetry is of the same size as the pi^+ asymmetry and shows a similar dependence on the relevant kinematic variables. The asymmetry is described by a phenomenological calculation based on a fragmentation function that represents sensitivity to the transverse polarization of the struck quark.Comment: 4 pages, 1 figure, replaced to correct eprint author field, 2nd replacement to correct figure; upper limit of model predictions are corrected. No correction to data or conclusion

Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry A1A_1

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry $A_1$. Longitudinally polarised positrons were scattered off a longitudinally polarised hydrogen target for values of $Q^2$ between 1.2 and 12 GeV$^2$ and values of $W^2$ between 1 and 4 GeV$^2$. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable $x$. This finding implies that the description of $A_1$ in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of $Q^2$ above 1.6 GeV$^2$.Comment: 5 pages, 1 eps figure, table added, new references added, in print in Phys. Rev. Let