Effect of blade geometry on the aerodynamic loads produced by vertical-axis wind turbines

Accurate aerodynamic modelling of vertical-axis wind turbines poses a significant challenge. The rotation of the turbine induces large variations in the angle of attack of its blades that can manifest as dynamic stall. In addition, interactions between the blades of the turbine and the wake that they produce can result in impulsive changes to the aerodynamic loading. The Vorticity Transport Model has been used to simulate the aerodynamic performance and wake dynamics of three different vertical-axis wind turbine configurations. It is known that vertical-axis turbines with either straight or curved blades deliver torque to their shaft that fluctuates at the blade passage frequency of the rotor. In contrast, a turbine with helically twisted blades delivers a relatively steady torque to the shaft. In this article, the interactions between helically twisted blades and the vortices within their wake are shown to result in localized perturbations to the aerodynamic loading on the rotor that can disrupt the otherwise relatively smooth power output that is predicted by simplistic aerodynamic tools that do not model the wake to sufficient fidelity. Furthermore, vertical-axis wind turbines with curved blades are shown to be somewhat more susceptible to local dynamic stall than turbines with straight blades

Geometric approach to Fletcher's ideal penalty function

Original article can be found at: www.springerlink.com Copyright Springer. [Originally produced as UH Technical Report 280, 1993]In this note, we derive a geometric formulation of an ideal penalty function for equality constrained problems. This differentiable penalty function requires no parameter estimation or adjustment, has numerical conditioning similar to that of the target function from which it is constructed, and also has the desirable property that the strict second-order constrained minima of the target function are precisely those strict second-order unconstrained minima of the penalty function which satisfy the constraints. Such a penalty function can be used to establish termination properties for algorithms which avoid ill-conditioned steps. Numerical values for the penalty function and its derivatives can be calculated efficiently using automatic differentiation techniques.Peer reviewe

Thermo-acoustic wave propagation and reflection near the liquid-gas critical point

We study the thermo-acoustic wave propagation and reflection near the liquid-gas critical point. Specifically, we perform a numerical investigation of the acoustic responses in a near-critical fluid to thermal perturbations based on the same setup of a recent ultrasensitive interferometry measurement in CO2 [Y. Miura et al. Phys. Rev. E 74, 010101(R) (2006)]. The numerical results agree well with the experimental data. New features regarding the reflection pattern of thermo-acoustic waves near the critical point under pulse perturbations are revealed by the proper inclusion of the critically diverging bulk viscosity.Comment: 14 pages, 4 figures, Accepted by PRE (Rapid Communication

High-risk Sexual Behavior is Associated with Post-Exposure Prophylaxis Non-adherence among Men who have Sex with Men Enrolled in a Combination Prevention Intervention.

Methamphetamine use among men who have sex with men (MSM) is associated with increased HIV prevalence, due to increased engagement in high-risk sexual behavior. Fifty-three HIV-negative, methamphetamine-using MSM were enrolled in a biobehavioral combination prevention intervention in Los Angeles, CA, to assess the feasibility of administering postexposure prophylaxis (PEP) in combination with contingency management (CM) to prevent HIV seroconversion. The study combined a CM behavioral intervention targeting reductions in methamphetamine use with a PEP biomedical intervention for HIV prevention. Those who reported recent exposure to HIV were initiated on tenofovir/emtricitabine- (Truvada)-based PEP (n=35). This secondary analysis sought to determine whether recent and/or lifetime sexual risk taking was associated with PEP adherence. Regression analyses controlling for participant sociodemographics demonstrated that, at baseline, increased number of lifetime sexually transmitted diseases (STDs; Coef.=-0.07; 95% CI=(-0.12) - (-0.01)) and recent episodes of unprotected anal intercourse (UAI; Coef.=-0.01; 95% CI= (-.01) - (-0.002)) were each associated with reductions in medication adherence. Given these associations between baseline sexual risk and PEP adherence, providers working with high-risk MSM may look to target reductions in sexual risk taking; this will reduce direct risk of HIV infection and may work to optimize medication adherence in the case of PEP initiation. Clinicaltrials.gov identifier: NCT00856323

Forces and atomic relaxations in the pSIC approach with ultrasoft pseudopotentials

We present the scheme that allows for efficient calculations of forces in the framework of pseudopotential self-interaction corrected (pSIC) formulation of the density functional theory. The scheme works with norm conserving and also with ultrasoft pseudopotentials and has been implemented in the plane-wave basis code {\sc quantum espresso}. We have performed tests of the internal consistency of the derived expressions for forces considering ZnO and CeO$_2$ crystals. Further, we have performed calculations of equilibrium geometry for LaTiO$_3$, YTiO$_3$, and LaMnO$_3$ perovskites and also for Re and Mn pairs in silicon. Comparison with standard DFT and DFT+U approaches shows that in the cases where spurious self-interaction matters, the pSIC approach predicts different geometry, very often closer to the experimental data.Comment: 11 pages, 2 figure

Same traits, different variance : Item-Level Variation Within Personality Measures

© 2014 the Author(s). This article has been published under the terms of the Creative Commons Attribution License. Without requesting permission from the Author or SAGE, you may further copy, distribute, transmit, and adapt the article, with the condition that the Author and SAGE Open are in each case credited as the source of the article. The version of record, Jamie S. Churcyard, Karen J. Pine, Shivani Sharma, Ben (C) Fletcher, ' Same Traits, Difference Variance: Item-Level Variation Within Personality Measures', SAGE Open, 2014, is available online via doi: 10.1177/2158244014522634Personality trait questionnaires are regularly used in individual differences research to examine personality scores between participants, although trait researchers tend to place little value on intra-individual variation in item ratings within a measured trait. The few studies that examine variability indices have not considered how they are related to a selection of psychological outcomes, so we recruited 160 participants (age M = 24.16, SD = 9.54) who completed the IPIP-HEXACO personality questionnaire and several outcome measures. Heterogenous within-subject differences in item ratings were found for every trait/facet measured, with measurement error that remained stable across the questionnaire. Within-subject standard deviations, calculated as measures of individual variation in specific item ratings within a trait/facet, were related to outcomes including life satisfaction and depression. This suggests these indices represent valid constructs of variability, and that researchers administering behavior statement trait questionnaires with outcome measures should also apply item-level variability indices.Peer reviewedFinal Published versio

Boiling a Unitary Fermi Liquid

We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy gives access to the energy, lifetime, and short-range correlations of Fermi polarons at low temperatures $T$. In this regime, we observe a characteristic $T^2$ dependence of the spectral width, corresponding to the quasiparticle decay rate expected for a Fermi liquid. At high $T$, the spectral width decreases again towards the scattering rate of the classical, unitary Boltzmann gas, $\propto T^{-1/2}$. In the transition region between the quantum degenerate and classical regime, the spectral width attains its maximum, on the scale of the Fermi energy, indicating the breakdown of a quasiparticle description. Density measurements in a harmonic trap directly reveal the majority dressing cloud surrounding the minority spins and yield the compressibility along with the effective mass of Fermi polarons.Comment: Accepted version at PR

Determination and development of cost effective techniques to monitor recreational catch and effort in Western Australian demersal finfish fisheries: Final Report for FRDC Project 2005/034 and WAMSI Subproject 4.4.3

Objectives1.Complete a series of concurrent catch and effort surveys of the West Coast Demersal Recreational Fishery using a variety of survey techniques.2.Compare the precision and accuracy of estimates generated using these various techniques3.Usingcostbenefitanalysis,produceaseriesofoptionstomonitorannualcatchandeffortfora range of precision levels and indicator species4.Development of cost effective methods for monitoring the catch of the non-commercial sector

Quantized charge pumping through a quantum dot by surface acoustic waves

We present a realization of quantized charge pumping. A lateral quantum dot is defined by metallic split gates in a GaAs/AlGaAs heterostructure. A surface acoustic wave whose wavelength is twice the dot length is used to pump single electrons through the dot at a frequency f=3GHz. The pumped current shows a regular pattern of quantization at values I=nef over a range of gate voltage and wave amplitude settings. The observed values of n, the number of electrons transported per wave cycle, are determined by the number of electronic states in the quantum dot brought into resonance with the fermi level of the electron reservoirs during the pumping cycle.Comment: 8 page