Influence of Finite Span and Sweep on Active Flow Control Efficacy

Active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations. On the standard configuration, stall commenced inboard, but with sweep the wing stalled initially near the tip. On both configurations, leading-edge perturbations increased CL,max and post stall lift, both with and without deflected flaps. Without sweep, the effect of control was approximately uniform across the wing span but remained effective to high angles of attack near the tip; when sweep was introduced a significant effect was noted inboard, but this effect degraded along the span and produced virtually no meaningful lift enhancement near the tip, irrespective of the tip configuration. In the former case, control strengthened the wingtip vortex; in the latter case, a simple semi-empirical model, based on the trajectory or "streamline" of the evolving perturbation, served to explain the observations. In the absence of sweep, control on finite-span flaps did not differ significantly from their nominally twodimensional counterpart. Control from the flap produced expected lift enhancement and CL,max improvements in the absence of sweep, but these improvements degraded with the introduction of sweep

ARPES and NMTO Wannier Orbital Theory of LiMo6_{6}O17_{17} - Implications for Unusually Robust Quasi-One Dimensional Behavior

We present the results of a combined study by band theory and angle resolved photoemission spectroscopy (ARPES) of the purple bronze, Li$_{1-x}$Mo$_{6}$O$_{17}$. Structural and electronic origins of its unusually robust quasi-one dimensional (quasi-1D) behavior are investigated in detail. The band structure, in a large energy window around the Fermi energy, is basically 2D and formed by three Mo $t_{2g}$-like extended Wannier orbitals, each one giving rise to a 1D band running at a 120$^\circ$ angle to the two others. A structural "dimerization" from $\mathbf{c}/2$ to $\mathbf{c}$ gaps the $xz$ and $yz$ bands while leaving the $xy$ bands metallic in the gap, but resonantly coupled to the gap edges and, hence, to the other directions. The resulting complex shape of the quasi-1D Fermi surface (FS), verified by our ARPES, thus depends strongly on the Fermi energy position in the gap, implying a great sensitivity to Li stoichiometry of properties dependent on the FS, such as FS nesting or superconductivity. The strong resonances prevent either a two-band tight-binding model or a related real-space ladder picture from giving a valid description of the low-energy electronic structure. We use our extended knowledge of the electronic structure to newly advocate for framing LiMo$_{6}$O$_{17}$ as a weak-coupling material and in that framework can rationalize both the robustness of its quasi-1D behavior and the rather large value of its Luttinger liquid (LL) exponent $\alpha$. Down to a temperature of 6$\,$K we find no evidence for a theoretically expected downward renormalization of perpendicular single particle hopping due to LL fluctuations in the quasi-1D chains.Comment: 53 pages, 17 Figures, 6 year

Non-Fermi liquid angle resolved photoemission lineshapes of Li0.9Mo6O17

A recent letter by Xue et al. (PRL v.83, 1235 ('99)) reports a Fermi-Liquid (FL) angle resolved photoemission (ARPES) lineshape for quasi one-dimensional Li0.9Mo6O17, contradicting our report (PRL v.82, 2540 ('99)) of a non-FL lineshape in this material. Xue et al. attributed the difference to the improved angle resolution. In this comment, we point out that this reasoning is flawed. Rather, we find that their data have fundamental differences from other ARPES results and also band theory.Comment: To be published as a PRL Commen

Electronic structure of sodium tungsten bronzes Na<SUB>x</SUB>WO<SUB>3</SUB> by high-resolution angle-resolved photoemission spectroscopy

The electronic structure of sodium tungsten bronzes, NaxWO3, for full range of x is investigated by high-resolution angle-resolved photoemission spectroscopy (HR-ARPES). The experimentally determined valence-band structure has been compared with the results of ab initio band-structure calculation. The HR-ARPES spectra taken in both the insulating and metallic phase of NaxWO3 reveal the origin of metal-insulator transition (MIT) in the sodium tungsten bronze system. In the insulating NaxWO3, the near-EF states are localized due to the strong disorder caused by the random distribution of Na+ ions in WO3 lattice. While the presence of an impurity band (level) induced by Na doping is often invoked to explain the insulating state found at low concentrations, there is no signature of impurity band (level) found from our results. Due to disorder and Anderson localization effect, there is a long-range Coulomb interaction of conduction electrons; as a result, the system is insulating. In the metallic regime, the states near EF are populated and the Fermi level shifts upward rigidly with increasing electron doping (x). The volume of electronlike Fermi surface (FS) at the &#915;(X) point gradually increases with increasing Na concentration due to W 5dt2g band filling. A rigid shift of EF is found to give a qualitatively good description of the FS evolution

Non-fermi-liquid single particle lineshape of the quasi-one-dimensional non-CDW metal Li_{0.9}Mo_{6}O_{17} : comparison to the Luttinger liquid

We report the detailed non-Fermi liquid (NFL) lineshape of the dispersing excitation which defines the Fermi surface (FS) for quasi-one-dimensional Li_{0.9}Mo_{6}O_{17}. The properties of Li_{0.9}Mo_{6}O_{17} strongly suggest that the NFL behavior has a purely electronic origin. Relative to the theoretical Luttinger liquid lineshape, we identify significant similarities, but also important differences.Comment: 5 pages, 3 eps figure

Pressure-induced structural transitions triggering dimensional crossover in lithium purple bronze Li0.9M6O17

At ambient pressure, lithium molybdenum purple bronze (Li0.9Mo6O17) is a quasi-one dimensional solid in which the anisotropic crystal structure and the linear dispersion of the underlying bands produced by electronic correlations possibly bring about a rare experimental realization of Tomomaga-Luttinger liquid physics. It is also the sole member of the broader purple molybdenum bronzes family where a Peierls instability has not been identified at low temperatures. The present study reports a pressure-induced series of phase transitions between 0 and 12 GPa. These transitions are strongly reflected in infrared spectroscopy, Raman spectroscopy, and x-ray diffraction. The most dramatic effect seen in optical conductivity is the metallization of the c-axis, concomitant to the decrease of conductivity along the b-axis. This indicates that high pressure drives the material away from its quasi-one dimensional behavior at ambient pressure. While the first pressure-induced structure of the series is resolved, the identification of the underlying mechanisms driving the dimensional change in the physics remains a challenge.Comment: 10 pages, 12 figure

Sometimes you have to take the person and show them how : adapting behavioral activation for peer recovery specialist-delivery to improve methadone treatment retention

BACKGROUND: Despite efficacy of medication for opioid use disorder, low-income, ethno-racial minoritized populations often experience poor opioid use disorder treatment outcomes. Peer recovery specialists, individuals with lived experience of substance use and recovery, are well-positioned to engage hard-to-reach patients in treatment for opioid use disorder. Traditionally, peer recovery specialists have focused on bridging to care rather than delivering interventions. This study builds on research in other low-resource contexts that has explored peer delivery of evidence-based interventions, such as behavioral activation, to expand access to care. METHODS: We sought feedback on the feasibility and acceptability of a peer recovery specialist-delivered behavioral activation intervention supporting retention in methadone treatment by increasing positive reinforcement. We recruited patients and staff at a community-based methadone treatment center and peer recovery specialist working across Baltimore City, Maryland, USA. Semi-structured interviews and focus groups inquired about the feasibility and acceptability of behavioral activation, recommendations for adaptation, and acceptability of working with a peer alongside methadone treatment. RESULTS: Participants (N = 32) shared that peer recovery specialist-delivered behavioral activation could be feasible and acceptable with adaptations. They described common challenges associated with unstructured time, for which behavioral activation could be particularly relevant. Participants provided examples of how a peer-delivered intervention could fit well in the context of methadone treatment, emphasizing the importance of flexibility and specific peer qualities. CONCLUSIONS: Improving medication for opioid use disorder outcomes is a national priority that must be met with cost-effective, sustainable strategies to support individuals in treatment. Findings will guide adaptation of a peer recovery specialist-delivered behavioral activation intervention to improve methadone treatment retention for underserved, ethno-racial minoritized individuals living with opioid use disorder

Edge and Bulk Transport in the Mixed State of a Type-II Superconductor

By comparing the voltage-current (V-I) curves obtained before and after cutting a sample of 2H-NbSe2, we separate the bulk and edge contributions to the transport current at various dissipation levels and derive their respective V- I curves and critical currents. We find that the edge contribution is thermally activated across a current dependent surface barrier. By contrast the bulk V-I curves are linear, as expected from the free flux flow model. The relative importance of bulk and edge contributions is found to depend on dissipation level and sample dimensions. We further show that the peak effect is a sharp bulk phenomenon and that it is broadened by the edge contribution

Dynamic separation on a pitching and surging airfoil as a model for flow over vertical axis wind turbine blades

Vertical axis wind turbine (VAWT) blades undergo dynamic separation due to the large angle of attack variation they experience during a turbine rotation. The flow over a single blade was modeled using a sinusoidally pitching and surging airfoil in a constant free stream flow at a mean chord Reynolds number of 10^5. Two-dimensional, time resolved velocity fields were acquired using particle image velocimetry (PIV). Vorticity contours were used to visualize shear layer and vortex activity. A low order model of dynamic separation was developed using Dynamic Mode Decomposition (DMD). A primary and secondary dynamic separation mode were identified as the critical drivers for the unsteady flow field

Generalized Spectral Signatures of Electron Fractionalization in Quasi-One and -Two Dimensional Molybdenum Bronzes and Superconducting Cuprates

We establish the quasi-one-dimensional Li purple bronze as a photoemission paradigm of Luttinger liquid behavior. We also show that generalized signatures of electron fractionalization are present in the angle resolved photoemission spectra for quasi-two-dimensional purple bronzes and certain cuprates. An important component of our analysis for the quasi-two-dimensional systems is the proposal of a ``melted holon'' scenario for the k-independent background that accompanies but does not interact with the peaks that disperse to define the Fermi surface.Comment: 7 pages, 8 figure