5,264 research outputs found
Hydraulic flow through a channel contraction: multiple steady states
We have investigated shallow water flows through a channel with a contraction by experimental and theoretical means. The horizontal channel consists of a sluice gate and an upstream channel of constant width ending in a linear contraction of minimum width . Experimentally, we observe upstream steady and moving bores/shocks, and oblique waves in the contraction, as single and multiple steady states, as well as a steady reservoir with a complex hydraulic jump in the contraction occurring in a small section of the and Froude number parameter plane. One-dimensional hydraulic theory provides a comprehensive leading-order approximation, in which a turbulent frictional parametrization is used to achieve quantitative agreement. An analytical and numerical analysis is given for two-dimensional supercritical shallow water flows. It shows that the one-dimensional hydraulic analysis for inviscid flows away from hydraulic jumps holds surprisingly well, even though the two-dimensional oblique hydraulic jump patterns can show large variations across the contraction channel
Macroscopic and Local Magnetic Moments in Si-doped CuGeO with Neutron and SR Studies
The temperature-concentration phase diagram of the Si-doped spin-Peierls
compound CuGeO is investigated by means of neutron scattering and muon
spin rotation spectroscopy in order to determine the microscopic distribution
of the magnetic and lattice dimerised regions as a function of doping. The
analysis of the zero-field muon spectra has confirmed the spatial inhomogeneity
of the staggered magnetisation that characterises the antiferromagnetic
superlattice peaks observed with neutrons. In addition, the variation of the
macroscopic order parameter with doping can be understood by considering the
evolution of the local magnetic moment as well as of the various regions
contributing to the muon signal
Pumilio binds para mRNA and requires nanos and brat to regulate sodium current in drosophila motoneurons
Homeostatic regulation of ionic currents is of paramount importance during periods of synaptic growth or remodeling. Our previous work has identified the translational repressor Pumilio (Pum) as a regulator of sodium current (INa) and excitability in Drosophila motoneurons. In this current study, we show that Pum is able to bind directly the mRNA encoding the Drosophila voltage-gated sodium channel paralytic (para). We identify a putative binding site for Pum in the 3' end of the para open reading frame (ORF). Characterization of the mechanism of action of Pum, using whole-cell patch clamp and real-time reverse transcription-PCR, reveals that the full-length protein is required for translational repression of para mRNA. Additionally, the cofactor Nanos is essential for Pum-dependent para repression, whereas the requirement for Brain Tumor (Brat) is cell type specific. Thus, Pum-dependent regulation of INa in motoneurons requires both Nanos and Brat, whereas regulation in other neuronal types seemingly requires only Nanos but not Brat. We also show that Pum is able to reduce the level of nanos mRNA and as such identify a potential negative-feedback mechanism to protect neurons from overactivity of Pum. Finally, we show coupling between INa (para) and IK (Shal) such that Pum-mediated change in para results in a compensatory change in Shal. The identification of para as a direct target of Pum represents the first ion channel to be translationally regulated by this repressor and the location of the binding motif is the first example in an ORF rather than in the canonical 3'-untranslated region of target transcripts
Using Virtual Observatory techniques to search for Adaptive Optics suitable AGN
Until recently, it has been possible only for nearby galaxies to study the
scaling relations between central black hole and host galaxy in detail. Because
of the small number densities at low redshift, (luminous) AGN are
underrepresented in such detailed studies. The advent of adaptive optics (AO)
at large telescopes helps overcoming this hurdle, allowing to reach small
linear scales over a wide range in redshift. Finding AO-suitable targets, i.e.,
AGN having a nearby reference star, and carrying out an initial multiwavelength
classification is an excellent use case for the Virtual Observatory. We present
our Virtual-Observatory approach to select an AO-suitable catalog of
X-ray-emitting AGN at redshifts 0.1<z<1.Comment: 4 pages, 5 figures, submitted to "EURO-VO AIDA workshop:
Multiwavelength astronomy and Virtual Observatory", ESAC, Spain, 1-3 Dec.
200
Effect of two gaps on the flux lattice internal field distribution: evidence of two length scales from muSR in Mg1-xAlxB2
We have measured the transverse field muon spin precession in the flux
lattice (FL) state of the two gap superconductor MgB2 and of the electron doped
compounds Mg1-xAlxB2 in magnetic fields up to 2.8T. We show the effect of the
two gaps on the internal field distribution in the FL, from which we determine
two coherence length parameters and the doping dependence of the London
penetration depth. This is an independent determination of the complex vortex
structure already suggested by the STM observation of large vortices in a MgB2
single crystal. Our data agrees quantitatively with STM and we thus validate a
new phenomenological model for the internal fields.Comment: now in press Phys. Rev. Lett., small modifications required by the
edito
Quenched crystal field disorder and magnetic liquid ground states in Tb2Sn2-xTixO7
Solid-solutions of the "soft" quantum spin ice pyrochlore magnets Tb2B2O7
with B=Ti and Sn display a novel magnetic ground state in the presence of
strong B-site disorder, characterized by a low susceptibility and strong spin
fluctuations to temperatures below 0.1 K. These materials have been studied
using ac-susceptibility and muSR techniques to very low temperatures, and
time-of-flight inelastic neutron scattering techniques to 1.5 K. Remarkably,
neutron spectroscopy of the Tb3+ crystal field levels appropriate to at high
B-site mixing (0.5 < x < 1.5 in Tb2Sn2-xTixO7) reveal that the doublet ground
and first excited states present as continua in energy, while transitions to
singlet excited states at higher energies simply interpolate between those of
the end members of the solid solution. The resulting ground state suggests an
extreme version of a random-anisotropy magnet, with many local moments and
anisotropies, depending on the precise local configuration of the six B sites
neighboring each magnetic Tb3+ ion.Comment: 6 pages, 6 figure
An experimental study on water surface profiles of high Froude number flows
Motivated by need to study supercritical overbank flows on floodplain, we experimentally investigate if initially supercritical flow in a rectangular flume would maintain its state throughout. Varying upstream gate opening, flow rate and angle of the slope, a total of 37 experimental cases were carried out. The experimental results are compared to two existing theories: an inviscid theory based on nonlinear shallow water equations and jump conditions and a hydraulic theory that takes friction into account. The experimental data are consistent with the two theories. Flows on downward slope were stable, while those on upward slope had unstable hydraulic jump and transformed into subcritical flow. The reported results should serve well in designing a laboratory flume with the supercritical inflow and in conducting hydraulic model experiments on overbank flows.OAIID:RECH_ACHV_DSTSH_NO:T201834776RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A080988CITE_RATE:.94FILENAME:2018KSCE22Park-etal.pdfDEPT_NM:건설환경공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/7f084c6c-e938-4359-acd7-76c6151612bc/linkN
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