An evaluation of a word analysis program for grade three.

Thesis (Ed.M.)--Boston Universit

Quasi-switched inverter using space vector pulse width modulation with triangular comparison for photovoltaic applications

Este trabajo analiza un prototipo para un inversor elevador cuasi-conmutado (qSBI) alimentando una carga resistiva aislada desde una fuente de CC. Se propone el uso de una modulación de ancho de pulso de vectores espaciales (SPWM) con comparación triangular que genera un incremento en el factor de ganancia del qSBI, y se contrasta su desempeño con otro tipo de modulaciones de vectores espaciales, tales como las modulaciones discontinuas. Para verificar la validez de la extensión de rango de tensión en el convertidor qSBI, se desarrolló una plataforma de pruebas semi-personalizada. Esta plataforma utiliza una tarjeta DSP de punto flotante (Analog Devices ADSP-21369) para el procesamiento de las estrategias de control, y una tarjeta de interfaz que incluye un arreglo lógico programable (FPGA) de Xilinx (Spartan-3), que permite desarrollar la modulación sincronizada que el qSBI necesita. Los resultados experimentales demuestran mejoras en el desempeño del convertidor qSBI en cuanto al factor de ganancia, reducción del estrés de voltaje en el capacitor y los perfiles de corriente de entrada. Las estrategias discontinuas de modulación del vector espacial no presentan un buen desempeño cuando se compara con las modulaciones continuas SVPWM o SPWM, ya que los niveles de rizado en las corrientes tomadas del módulo PV son de aproximadamente el doble que en el caso de las técnicas de modulación continuas. Finalmente, el uso del convertidor qSBI como microinversor es puesto en evidencia por dos casos experimentales prácticos de un sistema fotovoltaico PV con un algoritmo de ajuste del máximo punto de potencia (MPPT).This work analyzes a prototype of a quasi-switched boost inverter (qSBI) feeding an isolated resistive load from a DC source. The use of spatial vector pulse width modulation (SPWM) with triangular comparison is proposed to increase the qSBI gain factor, and its performance is contrasted with other types of spatial vector modulations, such as discontinuous modulations. To verify the validity of the method for voltage range extension in the qSBI converter, a semi-customized test platform was developed. This platform uses a DSP floating point card (Analog Devices ADSP-21369) for processing and control strategies and an interface card that includes a programmable logic array (FPGA) from Xilinx (Spartan-3), which allows to develop the synchronized modulation qSBI needs. The experimental results show improvements in the performance of the qSBI converter in terms of gain factor, voltage reduction in the capacitor, and input current profiles. Discontinuous space vector modulation strategies do not perform well when compared to continuous SVPWM or SPWM modulations, because the ripple levels in the currents taken from the PV module are approximately twice as great as in continuous modulation techniques. Finally, the usefulness of a qSBI as PV microinverter is confirmed by two practical experimental cases of a PV photovoltaic system with a maximum power point adjustment algorithm (MPPT)

The GALEX Arecibo SDSS survey: III. Evidence for the Inside-Out Formation of Galactic Disks

We analyze a sample of galaxies with stellar masses greater than $10^{10} M_{\odot}$ and with redshifts in the range $0.025<z<0.05$ for which HI mass measurements are available from the GALEX Arecibo SDSS Survey (GASS) or from the Arecibo Legacy Fast ALFA survey (ALFALFA). At a given value of $M_*$, our sample consists primarily of galaxies that are more HI-rich than average. We constructed a series of three control samples for comparison with these HI-rich galaxies. As expected, HI-rich galaxies differ strongly from galaxies of same stellar mass that are selected without regard to HI content. The majority of these differences are attributable to the fact that galaxies with more gas are bluer and more actively star-forming. In order to identify those galaxy properties that are causally connected with HI content, we compare results derived for the HI sample with those derived for galaxies matched in stellar mass, size and NUV-$r$ colour. The only photometric property that is clearly attributable to increasing HI content, is the colour gradient of the galaxy. Galaxies with larger HI fractions have bluer, more actively star-forming outer disks compared to the inner part of the galaxy. HI-rich galaxies also have larger $g$-band radii compared to $i$-band radii. Our results are consistent with the "inside-out" picture of disk galaxy formation, which has commonly served as a basis for semi-analytic models of the formation of disks in the context of Cold Dark Matter cosmologies. The lack of any intrinsic connection between HI fraction and galaxy asymmetry suggests that gas is accreted smoothly onto the outer disk.Comment: 18 pages, 20 figures. Accepted for publication in MNRAS. GASS publications and released data can be found at http://www.mpa-garching.mpg.de/GASS/index.ph

Penalization of aperture complexity in inversely planned volumetric modulated arc therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134774/1/mp2566.pd

The GALEX Arecibo SDSS Survey II: The Star Formation Efficiency of Massive Galaxies

We use measurements of the HI content, stellar mass and star formation rates in ~190 massive galaxies with stellar masses greater than 10^10 Msun, obtained from the Galex Arecibo SDSS Survey (GASS) described in Paper I (Catinella et al. 2010) to explore the global scaling relations associated with the bin-averaged ratio of the star formation rate over the HI mass, which we call the HI-based star formation efficiency (SFE). Unlike the mean specific star formation rate, which decreases with stellar mass and stellar mass surface density, the star formation efficiency remains relatively constant across the sample with a value close to SFE = 10^-9.5 yr^-1 (or an equivalent gas consumption timescale of ~3 Gyr). Specifically, we find little variation in SFE with stellar mass, stellar mass surface density, NUV-r color and concentration. We interpret these results as an indication that external processes or feedback mechanisms that control the gas supply are important for regulating star formation in massive galaxies. An investigation into the detailed distribution of SFEs reveals that approximately 5% of the sample shows high efficiencies with SFE > 10^-9 yr^-1, and we suggest that this is very likely due to a deficiency of cold gas rather than an excess star formation rate. Conversely, we also find a similar fraction of galaxies that appear to be gas-rich for their given specific star-formation rate, although these galaxies show both a higher than average gas fraction and lower than average specific star formation rate. Both of these populations are plausible candidates for "transition" galaxies, showing potential for a change (either decrease or increase) in their specific star formation rate in the near future. We also find that 36+/-5% of the total HI mass density and 47+/-5% of the total SFR density is found in galaxies with stellar mass greater than 10^10 Msun. [abridged]Comment: 18 pages, 11 figures. Accepted for publication in MNRAS. GASS publications and released data can be found at http://www.mpa-garching.mpg.de/GASS/index.ph

The GALEX Arecibo SDSS Survey. IV. Baryonic Mass-Velocity-Size Relations of Massive Galaxies

We present dynamical scaling relations for a homogeneous and representative sample of ~500 massive galaxies, selected only by stellar mass (>10^10 Msun) and redshift (0.025<z<0.05) as part of the ongoing GALEX Arecibo SDSS Survey. We compare baryonic Tully-Fisher (BTF) and Faber-Jackson (BFJ) relations for this sample, and investigate how galaxies scatter around the best fits obtained for pruned subsets of disk-dominated and bulge-dominated systems. The BFJ relation is significantly less scattered than the BTF when the relations are applied to their maximum samples, and is not affected by the inclination problems that plague the BTF. Disk-dominated, gas-rich galaxies systematically deviate from the BFJ relation defined by the spheroids. We demonstrate that by applying a simple correction to the stellar velocity dispersions that depends only on the concentration index of the galaxy, we are able to bring disks and spheroids onto the same dynamical relation -- in other words, we obtain a generalized BFJ relation that holds for all the galaxies in our sample, regardless of morphology, inclination or gas content, and has a scatter smaller than 0.1 dex. We find that disks and spheroids are offset in the stellar dispersion-size relation, and that the offset is removed when corrected dispersions are used instead. The generalized BFJ relation represents a fundamental correlation between the global dark matter and baryonic content of galaxies, which is obeyed by all (massive) systems regardless of morphology. [abridged]Comment: 20 pages, 15 figures. Accepted for publication in MNRAS. GASS publications and released data can be found at http://www.mpa-garching.mpg.de/GASS/index.ph

SafetyNet: streamlining and automating QA in radiotherapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/1/acm20387-sup-0002.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/2/acm20387.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/3/acm20387-sup-0003.pd

Use of plan quality degradation to evaluate tradeoffs in delivery efficiency and clinical plan metrics arising from IMRT optimizer and sequencer compromises

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135043/1/mp8118.pd

COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties

We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (D=100-200 Mpc), massive galaxies (log(M*/Msun)>10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with SDSS photometry and spectroscopy, GALEX imaging and high-quality Arecibo HI data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. The overall CO detection rate is 54%, but our survey also uncovers the existence of sharp thresholds in galaxy structural parameters such as stellar mass surface density and concentration index, below which all galaxies have a measurable cold gas component but above which the detection rate of the CO line drops suddenly. The mean molecular gas fraction MH2/M* of the CO detections is 0.066+/-0.039, and this fraction does not depend on stellar mass, but is a strong function of NUV-r colour. Through stacking, we set a firm upper limit of MH2/M*=0.0016+/-0.0005 for red galaxies with NUV-r>5.0. The average molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with significant scatter from one galaxy to the next. The existence of strong detection thresholds in both the HI and CO lines suggests that "quenching" processes have occurred in these systems. Intriguingly, atomic gas strongly dominates in the minority of galaxies with significant cold gas that lie above these thresholds. This suggests that some re-accretion of gas may still be possible following the quenching event.Comment: Accepted for publications in MNRAS. 32 pages, 25 figure

COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: II. The non-universality of the Molecular Gas Depletion Timescale

We study the relation between molecular gas and star formation in a volume-limited sample of 222 galaxies from the COLD GASS survey, with measurements of the CO(1-0) line from the IRAM 30m telescope. The galaxies are at redshifts 0.025<z<0.05 and have stellar masses in the range 10.0<log(M*/Msun)<11.5. The IRAM measurements are complemented by deep Arecibo HI observations and homogeneous SDSS and GALEX photometry. A reference sample that includes both UV and far-IR data is used to calibrate our estimates of star formation rates from the seven optical/UV bands. The mean molecular gas depletion timescale, tdep(H2), for all the galaxies in our sample is 1 Gyr, however tdep(H2) increases by a factor of 6 from a value of ~0.5 Gyr for galaxies with stellar masses of 10^10 Msun to ~3 Gyr for galaxies with masses of a few times 10^11 Msun. In contrast, the atomic gas depletion timescale remains contant at a value of around 3 Gyr. This implies that in high mass galaxies, molecular and atomic gas depletion timescales are comparable, but in low mass galaxies, molecular gas is being consumed much more quickly than atomic gas. The strongest dependences of tdep(H2) are on the stellar mass of the galaxy (parameterized as log tdep(H2)= (0.36+/-0.07)(log M* - 10.70)+(9.03+/-0.99)), and on the specific star formation rate. A single tdep(H2) versus sSFR relation is able to fit both "normal" star-forming galaxies in our COLD GASS sample, as well as more extreme starburst galaxies (LIRGs and ULIRGs), which have tdep(H2) < 10^8 yr. Normal galaxies at z=1-2 are displaced with respect to the local galaxy population in the tdep(H2) versus sSFR plane and have molecular gas depletion times that are a factor of 3-5 times longer at a given value of sSFR due to their significantly larger gas fractions.Comment: Accepted for publication in MNRAS. 19 pages, 11 figure