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

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

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

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

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

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

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with arXiv:0904.369

Breakdown of the Independent Particle Approximation in High-Energy Photoionization

The independent particle approximation is shown to break down for the photoionization of both inner and outer nℓ (ℓ\u3e0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed

Reexamining evidence-based practice in community corrections: beyond 'a confined view' of what works

This article aims to reexamine the development and scope of evidence-based practice (EBP) in community corrections by exploring three sets of issues. Firstly, we examine the relationships between the contested purposes of community supervision and their relationships to questions of evidence. Secondly, we explore the range of forms of evidence that might inform the pursuit of one purpose of supervision—the rehabilitation of offenders—making the case for a fuller engagement with “desistance” research in supporting this process. Thirdly, we examine who can and should be involved in conversations about EBP, arguing that both ex/offenders’ and practitioners’ voices need to be respected and heard in this debate

Lasing without inversion in three-level systems without external coherent driving

We have studied an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity. This system generates two laser fields, one of them without population inversion. Both ladder and V-type three-level schemes are considered with a ratio R=ωα/ωβ of inversionless laser frequency ωα to ordinary laser frequency ωβ of R=0.67 and R=1.88, respectively. Dual-wavelength lasing extends up to Doppler-broadening values for optical transitions of atoms in a vapor cell. Some considerations for the practical realization of this dual-wavelength laser are discussed