Stellar Populations in Barred Galaxies

We developed an iterative technique to better characterize stellar populations and the central activity of barred galaxies using evolutionary synthesis codes and OASIS data. The case of NGC5430 is presented here. Our results are reinforcing the role played by the bar and nuclear structures for the evolution of galaxies.Comment: 2 pages, 1 figure, to be published in the proceedings of IAU Symp. 262 "Stellar Populations - Planing for the Next Decate" (Aug. 2009

Constraining Stellar Feedback: Shock-ionized Gas in Nearby Starburst Galaxies

(abridged) We investigate the properties of feedback-driven shocks in 8 nearby starburst galaxies using narrow-band imaging data from the Hubble Space Telescope (HST). We identify the shock--ionized component via the line diagnostic diagram \oiii/\hb vs. \sii (or \nii)/\ha, applied to resolved regions 3--15 pc in size. We divide our sample into three sub-samples: sub-solar (Holmberg II, NGC 1569, NGC 4214, NGC 4449, and NGC 5253), solar (He 2-10, NGC 3077) and super-solar (NGC 5236) for consistent shock measurements. For the sub-solar sub-sample, we derive three scaling relations: (1) $L_{shock} \propto {SFR}^{~0.62}$, (2) $L_{shock} \propto {\Sigma_{SFR,HL}}^{~0.92}$, and (3) $L_{shock}/L_{tot} \propto {(L_H/L_{\odot,H})}^{-0.65}$, where $L_{shock}$ is the \ha luminosity from shock--ionized gas, ${\Sigma_{SFR,HL}}$ the SFR per unit half-light area, $L_{tot}$ the total \ha luminosity, and $L_H/L_{\odot,H}$ the absolute H-band luminosity from 2MASS normalized to solar luminosity. The other two sub--samples do not have enough number statistics, but appear to follow the first scaling relation. The energy recovered indicates that the shocks from stellar feedback in our sample galaxies are fully radiative. If the scaling relations are applicable in general to stellar feedback, our results are similar to those by Hopkins et al. (2012) for galactic super winds. This similarity should, however, be taken with caution at this point, as the underlying physics that enables the transition from radiative shocks to gas outflows in galaxies is still poorly understood.Comment: 29 pages, 14 figures, accepted for publication in the Ap

Physiological and clinical consequences of relief of right ventricular outflow tract obstruction late after repair of congenital heart defects.

BACKGROUND: Right ventricular outflow tract obstruction (RVOTO) is a common problem after repair of congenital heart disease. Percutaneous pulmonary valve implantation (PPVI) can treat this condition without consequent pulmonary regurgitation or cardiopulmonary bypass. Our aim was to investigate the clinical and physiological response to relieving RVOTO. METHODS AND RESULTS: We studied 18 patients who underwent PPVI for RVOTO (72% male, median age 20 years) from a total of 93 who had this procedure for various indications. All had a right ventricular outflow tract (RVOT) gradient >50 mm Hg on echocardiography without important pulmonary regurgitation (less than mild or regurgitant fraction <10% on magnetic resonance imaging [MRI]). Cardiopulmonary exercise testing, tissue Doppler echocardiography, and MRI were performed before and within 50 days of PPVI. PPVI reduced RVOT gradient (51.4 to 21.7 mm Hg, P<0.001) and right ventricular systolic pressure (72.8 to 47.3 mm Hg, P<0.001) at catheterization. Symptoms and aerobic (25.7 to 28.9 mL.kg(-1).min(-1), P=0.002) and anaerobic (14.4 to 16.2 mL.kg(-1).min(-1), P=0.002) exercise capacity improved. Myocardial systolic velocity improved acutely (tricuspid 4.8 to 5.3 cm/s, P=0.05; mitral 4.7 to 5.5 cm/s, P=0.01), whereas isovolumic acceleration was unchanged. The tricuspid annular velocity was not maintained on intermediate follow-up. Right ventricular end-diastolic volume (99.9 to 89.7 mL/m2, P<0.001) fell, whereas effective stroke volume (43.7 to 48.3 mL/m2, P=0.06) and ejection fraction (48.0% to 56.8%, P=0.01) increased. Left ventricular end-diastolic volume (72.5 to 77.4 mL/m2, P=0.145), stroke volume (45.3 to 50.6 mL/m2, P=0.02), and ejection fraction (62.6% to 65.8%, P=0.03) increased. CONCLUSIONS: PPVI relieves RVOTO, which leads to an early improvement in biventricular performance. Furthermore, it reduces symptoms and improves exercise tolerance. These findings have important implications for the management of this increasingly common condition

Percutaneous pulmonary valve implantation in humans - Results in 59 consecutive patients

Background - Right ventricular outflow tract (RVOT) reconstruction with valved conduits in infancy and childhood leads to reintervention for pulmonary regurgitation and stenosis in later life.Methods and Results - Patients with pulmonary regurgitation with or without stenosis after repair of congenital heart disease had percutaneous pulmonary valve implantation (PPVI). Mortality, hemodynamic improvement, freedom from explantation, and subjective and objective changes in exercise tolerance were end points. PPVI was performed successfully in 58 patients, 32 male, with a median age of 16 years and median weight of 56 kg. The majority had a variant of tetralogy of Fallot (n = 36), or transposition of the great arteries, ventricular septal defect with pulmonary stenosis (n = 8). The right ventricular (RV) pressure (64.4 +/- 17.2 to 50.4 +/- 14 mm Hg, P < 0.001), RVOT gradient (33 +/- 24.6 to 19.5 +/- 15.3, P < 0.001), and pulmonary regurgitation ( PR) (grade 2 of greater before, none greater than grade 2 after, P < 0.001) decreased significantly after PPVI. MRI showed significant reduction in PR fraction (21 +/- 13% versus 3 +/- 4%, P < 0.001) and in RV end-diastolic volume (EDV) (94 +/- 28 versus 82 +/- 24 mL (.) beat(-1) (.) m(-2), P < 0.001) and a significant increase in left ventricular EDV ( 64 +/- 12 versus 71 +/- 13 mL (.) beat(-1.) m(-2), P = 0.005) and effective RV stroke volume ( 37 +/- 7 versus 42 +/- 9 mL (.) beat(-1) (.) m(-2), P = 0.006) in 28 patients (age 19 +/- 8 years). A further 16 subjects, on metabolic exercise testing, showed significant improvement in V(O2)max (26 +/- 7 versus 29 +/- 6 mL (.) kg(-1) (.) min(-1), P < 0.001). There was no mortality.Conclusions - PPVI is feasible at low risk, with quantifiable improvement in MRI-defined ventricular parameters and pulmonary regurgitation, and results in subjective and objective improvement in exercise capacity

Optimally Scheduling Public Safety Power Shutoffs

In an effort to reduce power system-caused wildfires, utilities carry out public safety power shutoffs (PSPS) in which portions of the grid are de-energized to mitigate the risk of ignition. The decision to call a PSPS must balance reducing ignition risks and the negative impact of service interruptions. In this work, we consider three PSPS scheduling scenarios, which we model as dynamic programs. In the first two scenarios, we assume that N PSPSs are budgeted as part of the investment strategy. In the first scenario, a penalty is incurred for each PSPS declared past the Nth event. In the second, we assume that some costs can be recovered if the number of PSPSs is below $N$ while still being subject to a penalty if above N. In the third, the system operator wants to minimize the number of PSPS such that the total expected cost is below a threshold. We provide optimal or asymptotically optimal policies for each case, the first two of which have closed-form expressions. Lastly, we establish the applicability of the first PSPS model's policy to critical-peak pricing, and obtain an optimal scheduling policy to reduce the peak demand based on weather observations