Pattern formation in annular convection

This study of spatio-temporal pattern formation in an annulus is motivated by two physical problems on vastly different scales. The first is atmospheric convection in the equatorial plane between the warm surface of the Earth and the cold tropopause, modeled by the two dimensional Boussinesq equations. The second is annular electroconvection in a thin semetic film, where experiments reveal the birth of convection-like vortices in the plane as the electric field intensity is increased. This is modeled by two dimensional Navier-Stokes equations coupled with a simplified version of Maxwell's equations. The two models share fundamental mathematical properties and satisfy the prerequisites for application of O(2)-equivariant bifurcation theory. We show this can give predictions of interesting dynamics, including stationary and spatio-temporal patterns

Sensitivity, specificity, and sex differences in symptoms reported on the 13-item acute coronary syndrome checklist.

BackgroundClinical symptoms are part of the risk stratification approaches used in the emergency department (ED) to evaluate patients with suspected acute coronary syndromes (ACS). The objective of this study was to determine the sensitivity, specificity, and predictive value of 13 symptoms for a discharge diagnosis of ACS in women and men.Methods and resultsThe sample included 736 patients admitted to 4 EDs with symptoms suggestive of ACS. Symptoms were assessed with the 13-item validated ACS Symptom Checklist. Mixed-effects logistic regression models were used to estimate sensitivity, specificity, and predictive value of each symptom for a diagnosis of ACS, adjusting for age, obesity, diabetes, and functional status. Patients were predominantly male (63%) and Caucasian (70.5%), with a mean age of 59.7±14.2 years. Chest pressure, chest discomfort, and chest pain demonstrated the highest sensitivity for ACS in both women (66%, 66%, and 67%) and men (63%, 69%, and 72%). Six symptoms were specific for a non-ACS diagnosis in both women and men. The predictive value of shoulder (odds ratio [OR]=2.53; 95% CI=1.29 to 4.96) and arm pain (OR 2.15; 95% CI=1.10 to 4.20) in women was nearly twice that of men (OR=1.11; 95% CI=0.67 to 1.85 and OR=1.21; 95% CI=0.74 to 1.99). Shortness of breath (OR=0.49; 95% CI=0.30 to 0.79) predicted a non-ACS diagnosis in men.ConclusionsThere were more similarities than differences in symptom predictors of ACS for women and men

Electrically driven convection in a thin annular film undergoing circular Couette flow

We investigate the linear stability of a thin, suspended, annular film of conducting fluid with a voltage difference applied between its inner and outer edges. For a sufficiently large voltage, such a film is unstable to radially-driven electroconvection due to charges which develop on its free surfaces. The film can also be subjected to a Couette shear by rotating its inner edge. This combination is experimentally realized using films of smectic A liquid crystals. In the absence of shear, the convective flow consists of a stationary, azimuthally one-dimensional pattern of symmetric, counter-rotating vortex pairs. When Couette flow is applied, an azimuthally traveling pattern results. When viewed in a co-rotating frame, the traveling pattern consists of pairs of asymmetric vortices. We calculate the neutral stability boundary for arbitrary radius ratio $\alpha$ and Reynolds number ${{\cal R} e}$ of the shear flow, and obtain the critical control parameter ${\cal R}_c (\alpha, {{\cal R} e})$ and the critical azimuthal mode number ${m_c (\alpha, {{\cal R} e})}$. The Couette flow suppresses the onset of electroconvection, so that ${\cal R}_c (\alpha, {{\cal R} e}) > {\cal R}_c (\alpha,0)$. The calculated suppression is compared with experiments performed at $\alpha = 0.56$ and $0 \leq {{\cal R} e} \leq 0.22$.Comment: 17 pages, 2 column with 9 included eps figures. See also http://mobydick.physics.utoronto.c

Combustion synthesis of cadmium sulphide nanomaterials for efficient visible light driven hydrogen production from water

Anion-doped cadmium sulphide nanomaterials have been synthesized by using combustion method at normal atmospheric conditions. Oxidant/fuel ratios have been optimized in order to obtain CdS with best characteristics. Formation of CdS and size of crystallite were identified by X-ray diffraction and confirmed by transmission electron microscopy. X-ray photoelectron spectroscopy confirmed the presence of C and N in the CdS matrix. The observed enhanced photocatalytic activity of the CdS nanomaterials for the hydrogen production from water (2120 μmol/h) can be attributed to high crystallinity, low band gap and less exciton recombination due to the C and N doping

Localized states in sheared electroconvection

Electroconvection in a thin, sheared fluid film displays a rich sequence of bifurcations between different flow states as the driving voltage is increased. We present a numerical study of an annular film in which a radial potential difference acts on induced surface charges to drive convection. The film is also sheared by independently rotating the inner edge of the annulus. This simulation models laboratory experiments on electroconvection in sheared smectic liquid crystal films. The applied shear competes with the electrical forces, resulting in oscillatory and strongly subcritical bifurcations between localized vortex states close to onset. At higher forcing, the flow becomes chaotic via a Ruelle-Takens-Newhouse scenario. The simulation allows flow visualization not available in the physical experiments, and sheds light on previously observed transitions in the current-voltage characteristics of electroconvecting smectic films.Comment: To be published in EuroPhysics Letters, 6 pages, 6 figures: final versio

Economic Dan Emission Dispatch Pada Sistem Kelistrikan 500 KV Jawa-Bali Menggunakan Composite Generation Cost Function Dengan Metode Cuckoo Optimization Algorithm

Permintaan daya listrik yang terus bertambah menyebabkan daya listrik yang disuplai oleh pembangkit menjadi lebih besar. Kondisi beban yang harus disuplai pembangkit selalu berubah-ubah tiap waktunya, maka penyaluran energi listrik haruslah sesuai antara energi yang terbangkitkan oleh pembangkit dengan jumlah beban yang harus disuplai untuk memperoleh biaya pembangkitan yang paling ekonomis. Pada Tugas Akhir ini untuk mendapatkan biaya yang ekonomis akan dilakukan optimasi pembangkit sehingga didapatkan nilai pembangkitan yang paling optimal. Pengoptimalan pembangkit bertujuan untuk mendapatkan biaya operasional yang minimum tetapi tetap dapat memenuhi permintaan beban yang ada. Penggunaan generator dengan bahan bakar fosil dapat memberikan efek pencemaran lingkungan akibat emisi sisa dari pembakaran. Proses optimasi akan membuat jumlah bahan bakar yang digunakan dapat diminimalisir sehingga akan mengurangi emisi yang dihasilkan oleh pembangkit

Target Mass Monitoring and Instrumentation in the Daya Bay Antineutrino Detectors

The Daya Bay experiment measures sin^2 2{\theta}_13 using functionally identical antineutrino detectors located at distances of 300 to 2000 meters from the Daya Bay nuclear power complex. Each detector consists of three nested fluid volumes surrounded by photomultiplier tubes. These volumes are coupled to overflow tanks on top of the detector to allow for thermal expansion of the liquid. Antineutrinos are detected through the inverse beta decay reaction on the proton-rich scintillator target. A precise and continuous measurement of the detector's central target mass is achieved by monitoring the the fluid level in the overflow tanks with cameras and ultrasonic and capacitive sensors. In addition, the monitoring system records detector temperature and levelness at multiple positions. This monitoring information allows the precise determination of the detectors' effective number of target protons during data taking. We present the design, calibration, installation and in-situ tests of the Daya Bay real-time antineutrino detector monitoring sensors and readout electronics.Comment: 22 pages, 20 figures; accepted by JINST. Changes in v2: minor revisions to incorporate editorial feedback from JINS

Bifurcations in annular electroconvection with an imposed shear

We report an experimental study of the primary bifurcation in electrically-driven convection in a freely suspended film. A weakly conducting, submicron thick smectic liquid crystal film was supported by concentric circular electrodes. It electroconvected when a sufficiently large voltage $V$ was applied between its inner and outer edges. The film could sustain rapid flows and yet remain strictly two-dimensional. By rotation of the inner electrode, a circular Couette shear could be independently imposed. The control parameters were a dimensionless number ${\cal R}$, analogous to the Rayleigh number, which is $\propto V^2$ and the Reynolds number ${\cal R}e$ of the azimuthal shear flow. The geometrical and material properties of the film were characterized by the radius ratio $\alpha$, and a Prandtl-like number ${\cal P}$. Using measurements of current-voltage characteristics of a large number of films, we examined the onset of electroconvection over a broad range of $\alpha$, ${\cal P}$ and ${\cal R}e$. We compared this data quantitatively to the results of linear stability theory. This could be done with essentially no adjustable parameters. The current-voltage data above onset were then used to infer the amplitude of electroconvection in the weakly nonlinear regime by fitting them to a steady-state amplitude equation of the Landau form. We show how the primary bifurcation can be tuned between supercritical and subcritical by changing $\alpha$ and ${\cal R}e$.Comment: 17 pages, 12 figures. Submitted to Phys. Rev. E. Minor changes after refereeing. See also http://mobydick.physics.utoronto.c

Experimental Status of Neutrino Physics

After a fascinating phase of discoveries, neutrino physics still has a few mysteries such as the absolute mass scale, the mass hierarchy, the existence of CP violation in the lepton sector and the existence of right-handed neutrinos. It is also entering a phase of precision measurements. This is what motivates the NUFACT 11 conference which prepares the future of long baseline neutrino experiments. In this paper, we report the status of experimental neutrino physics. We focus mainly on absolute mass measurements, oscillation parameters and future plans for oscillation experiments