Flow Visualization Studies on Drag-Reducing Turbulent Flows

Flow visualisation studies in a square duct of internal dimensions 44.5 x 44.5 mm are reported. The flow marker is a stream of opaque white dye, released from a downstream facing stationary tube, and it is photographed through the plexiglass wall of the duct. The point of dye release can be traversed in a direction perpendicular to the duct wall and three locations are investigated, two in the core of the flow and one in the near- wall region. By using Is exposure times photographs are obtained of a dye dispersion cone and the cone angle is measured and related to the turbulence properties of the flow. Using water as the solvent various concentrations of the highly effective drag reducing polymer Polyox WSR-301 are explored and relationships obtained between cone angle and injection location, Reynolds number and drag reduction. The importance of turbulence suppression in the near-wall region of the flow is demonstrated to be closely linked with the drag reduction mechanism

Hydrodynamic Behaviour of a Two-Stage Channel with Horizontal and Inclined Floodplains: A Numerical Investigation

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Discharge and force distribution in a sinuous channel with vegetated floodplains during overbank flow

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on 2019, available online at: http://www.tandfonline.com/10.1080/00221686.2019.1581667Overbank flow in a sinuous channel with roughened floodplains has been investigated, focusing on the effect of floodplain vegetation on overall flow resistance. The physical model of the Besòs River has allowed analysing the effect of flexible roughness elements which simulate the natural vegetation of rivers. The experimental measurements of horizontal velocities have been used to obtain zonal discharges and forces along a meander wavelength. The results illustrate that although mass transfer is the most important source of energy losses, in rivers with strongly vegetated floodplains the flow resistance increases considerably due to the strong apparent shear forces acting between the main channel and floodplains.Peer ReviewedPostprint (author's final draft

Relativistic Hartree-Bogoliubov description of the deformed ground-state proton emitters

Ground-state properties of deformed proton-rich odd-Z nuclei in the region $59 \leq Z \leq 69$ are described in the framework of Relativistic Hartree Bogoliubov (RHB) theory. One-proton separation energies and ground-state quadrupole deformations that result from fully self-consistent microscopic calculations are compared with available experimental data. The model predicts the location of the proton drip-line, the properties of proton emitters beyond the drip-line, and provides information about the deformed single-particle orbitals occupied by the odd valence proton.Comment: 9 pages, RevTeX, 3 PS figures, submitted Phys. Rev. Letter

Beyond the Dipole Approximation: Angular-Distribution Effects in the 1s Photoemission from Small Molecules

Over the past two decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Recent experiments on the 1s inner shells of small molecules at relatively low photon energies (⩽ 1000 eV) show strong nondipole effects. They are significant and measurable at energies close to threshold, in conflict with a common assumption that the dipole approximation is valid for photon energies below 1 keV

Large Nondipole Effects in the Angular Distributions of K-Shell Photoelectrons from Molecular Nitrogen

Measurements of angular distributions of K-shell electrons photoejected from molecular nitrogen are reported which reveal large deviations at relatively low photon energies ( ħω≤500eV) from emission patterns anticipated from the dipole approximation to interactions between radiation and matter. A concomitant theoretical analysis incorporating the effects of electromagnetic retardation attributes the observed large nondipole behaviors in N2 to bond-length-dependent terms in the E1⊗(E2,M1) photoelectron emission amplitudes which are indicative of a potentially universal nondipole behavior in molecular photoionization

An Integrated and Novel Approach to Estimating the Conveyance Capacity of the River Blackwater

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Gain without population inversion in V-type systems driven by a frequency-modulated field

We obtain gain of the probe field at multiple frequencies in a closed three-level V-type system using frequency modulated pump field. There is no associated population inversion among the atomic states of the probe transition. We describe both the steady-state and transient dynamics of this system. Under suitable conditions, the system exhibits large gain simultaneously at series of frequencies far removed from resonance. Moreover, the system can be tailored to exhibit multiple frequency regimes where the probe experiences anomalous dispersion accompanied by negligible gain-absorption over a large bandwidth, a desirable feature for obtaining superluminal propagation of pulses with negligible distortion.Comment: 10 pages + 8 figures; To appear in Physical Review

Electric-octupole and pure-electric-quadrupole effects in soft-x-ray photoemission

Second-order [O(k^2), k=omega/c] nondipole effects in soft-x-ray photoemission are demonstrated via an experimental and theoretical study of angular distributions of neon valence photoelectrons in the 100--1200 eV photon-energy range. A newly derived theoretical expression for nondipolar angular distributions characterizes the second-order effects using four new parameters with primary contributions from pure-quadrupole and octupole-dipole interference terms. Independent-particle calculations of these parameters account for a significant portion of the existing discrepancy between experiment and theory for Ne 2p first-order nondipole parameters.Comment: 4 pages, 3 figure