Air and water flows in a vertical sand column

The unsteady state drainage of water from a vertical sand column with and without a finer layer on the top was studied theoretically and experimentally to investigate the airflow generated by the finer layer. The sand column, saturated at its lower portion and initially in the condition of hydrostatic equilibrium, is drained at its bottom at constant head. The results show that significant vacuum can be generated in the vadose zone of the column with a finer layer on the top. The vacuum increases quickly in the earlier stage of the drainage, reaches a maximum, and gradually becomes zero. Because of the effect of the vacuum in the vadose zone, water is held in and the cumulative outflow from the column with the finer layer is much smaller than without the layer during most of the drainage process. Ordinary differential equations (ODE), which require only saturated hydraulic properties of the porous media, are derived to predict the location of the surface of saturation and vacuum in the vadose zone in air-water two-phase flow. The solutions of ODE match very satisfactorily with the experimental data and give better results than TOUGH2. Copyright 2011 by the American Geophysical Union.published_or_final_versio

Reduced dynamics with renormalization in solid-state charge qubit measurement

Quantum measurement will inevitably cause backaction on the measured system, resulting in the well known dephasing and relaxation. In this report, in the context of solid--state qubit measurement by a mesoscopic detector, we show that an alternative backaction known as renormalization is important under some circumstances. This effect is largely overlooked in the theory of quantum measurement.Comment: 12 pages, 4 figure

Standardizing type Ia supernovae optical brightness using near-infrared rebrightening time

Accurate standardization of Type Ia supernovae (SNIa) is instrumental to the usage of SNIa as distance indicators. We analyse a homogeneous sample of 22 low-z SNIa, observed by the Carnegie Supernova Project in the optical and near-infrared (NIR). We study the time of the second peak in the J band, t2, as an alternative standardization parameter of SNIa peak optical brightness, as measured by the standard SALT2 parameter mB. We use BAHAMAS, a Bayesian hierarchical model for SNIa cosmology, to estimate the residual scatter in the Hubble diagram. We find that in the absence of a colour correction, t2 is a better standardization parameter compared to stretch: t2 has a 1\u3c3 posterior interval for the Hubble residual scatter of \u3c3\u394\u3bc = (0.250, 0.257) mag, compared to \u3c3\u394\u3bc = (0.280, 0.287) mag when stretch (x1) alone is used. We demonstrate that when employed together with a colour correction, t2 and stretch lead to similar residual scatter. Using colour, stretch and t2 jointly as standardization parameters does not result in any further reduction in scatter, suggesting that t2 carries redundant information with respect to stretch and colour. With a much larger SNIa NIR sample at higher redshift in the future, t2 could be a useful quantity to perform robustness checks of the standardization procedure

Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis

Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.Tao Ling, Dong-Yang Yan, Yan Jiao, Hui Wang, Yao Zheng, Xueli Zheng, Jing Mao, Xi-Wen Du, Zhenpeng Hu, Mietek Jaroniec, Shi-Zhang Qia

Direct Measurements of the Branching Fractions for Inclusive K±K^\pm and Inclusive Semileptonic Decays of D+D^+ and D0D^0 Mesons

With singly-tagged $\bar D$ samples selected from the data collected at and around 3.773 GeV with the BESII detector at the BEPC collider, we have measured the branching fractions for the inclusive $K^\pm$ decays of $D^+$ and $D^0$ mesons, which are $BF(D^+\to K^-X) = (24.7 \pm 1.3 \pm 1.2)$, $BF(D^+\to K^+X) = (6.1 \pm 0.9 \pm 0.4)$, $BF(D^0\to K^-X) = (57.8 \pm 1.6 \pm 3.2)$ and $BF(D^0\to K^+X) = (3.5 \pm 0.7 \pm 0.3)$, respectively. We have also measured the branching fractions for the inclusive semileptonic decays of $D^+$ and $D^0$ mesons to be $BF(D^+ \to e^+ X)=(15.2 \pm 0.9 \pm 0.8)$ and $BF(D^0 \to e^+ X) =(6.3 \pm 0.7 \pm 0.4)$. These yield the ratio of their partial widths to be $\Gamma(D^+ \to e^+X)/\Gamma(D^0 \to e^+X)=0.95 \pm 0.12 \pm 0.07$.Comment: 6 pages, 5 figure

"Narrow" Graphene Nanoribbons Made Easier by Partial Hydrogenation

It is a challenge to synthesize graphene nanoribbons (GNRs) with narrow widths and smooth edges in large scale. Our first principles study on the hydrogenation of GNRs shows that the hydrogenation starts from the edges of GNRs and proceeds gradually toward the middle of the GNRs so as to maximize the number of carbon-carbon $\pi$-$\pi$ bonds. Furthermore, the partially hydrogenated wide GNRs have similar electronic and magnetic properties as those of narrow GNRs. Therefore, it is not necessary to directly produce narrow GNRs for realistic applications because partial hydrogenation could make wide GNRs "narrower"