A dimensional analysis of supersaturated total dissolved gas dissipation

Elevated levels of total dissolved gas (TDG) may occur downstream of dam discharges, leading to increased incidence of gas bubble disease in fish. Accelerating the dissipation of supersaturated TDG in the downstream river can mitigate this negative problem. However, developing effective mitigation techniques is hampered by limitations in present models of TDG dissipation processes. Furthermore, data useful for modelling the dissipation of supersaturated TDG through the free surface in natural rivers are limited. Past studies indicated that the TDG dissipation process is quantitatively different from the reaeration process, and TDG behavior is quantitatively different from dissolved oxygen. However, a correct parameterization of the TDG dissipation process is still missing. The paper presents a novel dimensional analysis of the dissipation of supersaturated TDG. This approach can provide a relationship between the TDG dissipation coefficient and some classical fluid mechanics index-numbers. This dimensional analysis considers some key parameters for the dissipation process both water and TDG properties as well as flow characteristics, including turbulence. These parameters are water kinematic viscosity, TDG molecular diffusivity and vertical turbulent diffusivity, and channel width. The application of dimensional analysis pointed out that the TDG dissipation coefficient is a function of the Schmidt number, the aspect ratio of the channel, and the shear Reynolds number. The dimensional analysis was then verified using both field data collected in some large natural rivers and reservoirs in Sichuan and experimental data in laboratory flume at State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University. The analysis revealed the key role of turbulence in controlling the TDG dissipation while the importance of gas/water characteristics remains still unclear and needs further investigations

H2_2 ortho-to-para conversion on grains: A route to fast deuterium fractionation in dense cloud cores?

Deuterium fractionation, i.e. the enhancement of deuterated species with respect to the non-deuterated ones, is considered to be a reliable chemical clock of star-forming regions. This process is strongly affected by the ortho-to-para (o-p) H$_2$ ratio. In this letter we explore the effect of the o-p H$_2$ conversion on grains on the deuteration timescale in fully depleted dense cores, including the most relevant uncertainties that affect this complex process. We show that (i) the o-p H$_2$ conversion on grains is not strongly influenced by the uncertainties on the conversion time and the sticking coefficient and (ii) that the process is controlled by the temperature and the residence time of ortho-H$_2$ on the surface, i.e. by the binding energy. We find that for binding energies in between 330-550 K, depending on the temperature, the o-p H$_2$ conversion on grains can shorten the deuterium fractionation timescale by orders of magnitude, opening a new route to explain the large observed deuteration fraction $D_\mathrm{frac}$ in dense molecular cloud cores. Our results suggest that the star formation timescale, when estimated through the timescale to reach the observed deuteration fractions, might be shorter than previously proposed. However, more accurate measurements of the binding energy are needed to better assess the overall role of this process.Comment: Accepted for publication in ApJ Letter

Adiabatic connection at negative coupling strengths

The adiabatic connection of density functional theory (DFT) for electronic systems is generalized here to negative values of the coupling strength $\alpha$ (with {\em attractive} electrons). In the extreme limit $\alpha\to-\infty$ a simple physical solution is presented and its implications for DFT (as well as its limitations) are discussed. For two-electron systems (a case in which the present solution can be calculated exactly), we find that an interpolation between the limit $\alpha\to-\infty$ and the opposite limit of infinitely strong repulsion ($\alpha\to+\infty$) yields a rather accurate estimate of the second-order correlation energy E\cor\glt[\rho] for several different densities $\rho$, without using virtual orbitals. The same procedure is also applied to the Be isoelectronic series, analyzing the effects of near-degeneracy.Comment: 9 pages, submitted to PR

Long-term Labor Force Exit and Economic Well-being: A Cross-National Comparison of Public and Private Income Support

N/A

Alx1, a member of the Cart1/Alx3/Alx4 subfamily of Paired-class homeodomain proteins, is an essential component of the gene network controlling skeletogenic fate specification in the sea urchin embryo

In the sea urchin embryo, the large micromeres and their progeny function as a critical signaling center and execute a complex morphogenetic program. We have identified a new and essential component of the gene network that controls large micromere specification, the homeodomain protein Alx1. Alx1 is expressed exclusively by cells of the large micromere lineage beginning in the first interphase after the large micromeres are born. Morpholino studies demonstrate that Alx1 is essential at an early stage of specification and controls downstream genes required for epithelial-mesenchymal transition and biomineralization. Expression of Alx1 is cell autonomous and regulated maternally through ß-catenin and its downstream effector, Pmar1. Alx1 expression can be activated in other cell lineages at much later stages of development, however, through a regulative pathway of skeletogenesis that is responsive to cell signaling. The Alx1 protein is highly conserved among euechinoid sea urchins and is closely related to the Cart1/Alx3/Alx4 family of vertebrate homeodomain proteins. In vertebrates, these proteins regulate the formation of skeletal elements of the limbs, face and neck. Our findings suggest that the ancestral deuterostome had a population of biomineral-forming mesenchyme cells that expressed an Alx1-like protein

Perfect quantum transport in arbitrary spin networks

Spin chains have been proposed as wires to transport information between distributed registers in a quantum information processor. Unfortunately, the challenges in manufacturing linear chains with engineered couplings has hindered experimental implementations. Here we present strategies to achieve perfect quantum information transport in arbitrary spin networks. Our proposal is based on the weak coupling limit for pure state transport, where information is transferred between two end-spins that are only weakly coupled to the rest of the network. This regime allows disregarding the complex, internal dynamics of the bulk network and relying on virtual transitions or on the coupling to a single bulk eigenmode. We further introduce control methods capable of tuning the transport process and achieve perfect fidelity with limited resources, involving only manipulation of the end-qubits. These strategies could be thus applied not only to engineered systems with relaxed fabrication precision, but also to naturally occurring networks; specifically, we discuss the practical implementation of quantum state transfer between two separated nitrogen vacancy (NV) centers through a network of nitrogen substitutional impurities.Comment: 5+7 page

X-ray Properties of Low-Mass Pre-Main Sequence Stars in the Orion Trapezium Cluster

The Chandra High Energy Transmission Gratings (HETG) Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster which provides high resolution X-ray spectra of very young stars over a wide mass range (0.7 - 2.3 Msun). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts which are well-characterized at optical and infra-red wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above $10^{31}$ erg/s, in some cases exceeding $10^{32}$ erg/s for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total EMs range between 3 - 8$\times10^{54}$ cm$^{-3}$ and are comparable to active coronal sources. Limits on the forbidden to inter-combination line ratios in the He-Like K-shell lines show that we observe a predominantely optically thin plasma with electron densities below $10^{12}$ cm$^{-3}$. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6 to 2.3 Msun classical T Tauri stars shows that coronal activity and possibly coronal loop size increase significantly between ages 0.1 to 10 Myrs.Comment: 13 pages, 12 figures, submitted to the Astrophysical Journa