A theory for image persistence in HgCdTe photodiodes

Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli

A new deep-depletion CCD for the red channel of the Palomar Double Spectrograph

The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been upgraded with a new deep-depletion CCD from LBNL. Its redder response produced a significant increase of the throughput above 550 nm, and its longer dimension more than doubled the spectral coverage. A special Dewar was designed to accommodate a detector mount which includes features to minimize CCD motion due to thermal cycling, in spite of the very simple "picture frame" packaging of the CCD. The new Dewar also includes some novel features to improve the liquid nitrogen hold time while staying within the size envelope allowed in the Cassegrain cage. We describe these changes along with the detector characterization

A theory for image persistence in HgCdTe photodiodes

Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli

The Milky Way like galaxy NGC 6384 and its nuclear star cluster at high NIR spatial resolution using LBT/ARGOS commissioning data

We analyse high spatial resolution near infra-red (NIR) imaging of NGC6384, a Milky Way like galaxy, using ARGOS commissioning data at the Large Binocular Telescope (LBT). ARGOS provides a stable PSF$_{\rm FWHM}\!=\!0.2"\!-\!0.3"$ AO correction of the ground layer across the LUCI2 NIR camera $4'\!\times4'$ field by using six laser guide stars (three per telescope) and a natural guide star for tip-tilt sensing and guiding. Enabled by this high spatial resolution we analyse the structure of the nuclear star cluster (NSC) and the central kiloparsec of NGC6384. We find via 2D modelling that the NSC ($r_{\rm eff}\!\simeq\!10$pc) is surrounded by a small ($r_{\rm eff}\!\simeq\!100$pc) and a larger Sersi\'c ($r_{\rm eff}\!\simeq\!400$pc), all embedded within the NGC\,6384 large-scale boxy/X-shaped bulge and disk. This proof-of-concept study shows that with the high spatial resolution achieved by ground-layer AO we can push such analysis to distances previously only accessible from space. SED-fitting to the NIR and optical HST photometry allowed to leverage the age-metallicity-extinction degeneracies and derive the effective NSC properties of an young to old population mass ratio of $8\%$ with ${\cal M}_{\rm\star,old}\!\simeq\!3.5\times10^7M_\odot$, Age$_{\rm old,\ young}\!=\!10.9\pm1.3$Gyr and 226\,Myr$\pm62\%$, metallicity [M/H]$=\!-0.11\pm0.16$and$0.33\pm39\%$dex, and$E(B\!-\!V)\!=\!0.63$ and 1.44mag.Comment: 12 pages (+9 appendix), 11 figures, Accepted in MNRA

Rapidly decaying supernova 2010X: A candidate ".Ia" explosion

We present the discovery, photometric, and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with τ_d = 5 days and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M_r = −17 mag and has mean velocities of 10,000 km s^(−1). Our light curve modeling suggests a radioactivity-powered event and an ejecta mass of 0.16M_⊙. If powered by Nickel, we show that the Nickel mass must be very small (≈0.02 M_⊙) and that the supernova quickly becomes optically thin to γ -rays. Our spectral modeling suggests that SN 2010X and SN 2002bj have similar chemical compositions and that one of aluminum or helium is present. If aluminum is present, we speculate that this may be an accretion-induced collapse of an O-Ne-Mg white dwarf. If helium is present, all observables of SN 2010X are consistent with being a thermonuclear helium shell detonation on a white dwarf, a “.Ia” explosion. With the 1 day dynamic-cadence experiment on the Palomar Transient Factory, we expect to annually discover a few such events

Otimização multiobjetivo do arranjo de um painel estrutural submetido a pressão uniforme, utilizando o método dos elementos finitos

TCC (graduação) - Universidade Federal de Santa Catarina. Campus Joinville. Engenharia Naval.O mercado de embarcações navais está cada vez mais competitivo. Esta disputa instiga engenheiros à busca de processos eficientes no corte de custos. O uso de técnicas de otimização vem se mostrando uma poderosa estratégia no processo de tomada de decisão. Nesse contexto, propõe-se a aplicação de técnicas de otimização ao projeto da unidade básica que compõe a estrutura de um navio, o painel estrutural. O objetivo é um projeto eficiente, resultando em melhor aproveitamento dos materiais e dos processos de fabricação. O painel estrutural corresponde a uma porção continua de chapa reforçada por perfis ortogonais. A otimização da eficiência passa pela determinação de diversas variáveis de decisão, como espessura de chapa e geometria e espaçamentos dos reforçadores. A análise estrutural considerou o painel com extremidades engastadas e apoiadas, submetido a uma pressão uniforme. A determinação do campo de tensões da estrutura empregou o Método dos Elementos Finitos, com elementos de casca e viga, utilizando o Ansys Workbench. Por fim utilizou-se o algoritmo genético NSGA-II para buscar a topologia ótima da estrutura. Foram realizadas diferentes abordagens de otimização, buscando a minimização da massa, tensão e comprimento de solda. A verificação do tamanho da população inicial (DOE), mostrou que uma população correspondendo a 5% do máximo de análises permitidas, resultou na Fronteira de Pareto dominante e com maior número de indivíduos ótimos. Os indivíduos de Pareto apresentam uma tendência de possuírem 2 reforçadores pesados longitudinais. Foi verificado que vários indivíduos ótimos possuem um comprimento mínimo comum com diferentes massas estruturais

Household characteristics and poverty: an application of support vector machines

El uso de técnicas cuantitativas para la clasificación de segmentos poblacionales es una fase crítica para evaluar sus condiciones de materiales de existencia, información que sirve como input para los procesos de planificación de estrategias dirigidas a paliar la pobreza y la intervención discrecional de tales grupos, bajo los criterios de racionalidad económica e instrumental. En este artículo se construye un modelo de máquinas de soporte vectorial, entendido éste como un algoritmo de aprendizaje supervisado que proporciona un clasificador lineal no probabilístico con un superlativo nivel de precisión. De este modo, se segmenta una muestra de núcleos familiares residentes en Cartagena de Indias, en función de ciertas variables económicas y sociodemográficas. La obtención de los resultados analíticos refrenda el hecho de que los factores con mayor poder de discriminación entre los agentes económicos son el estatus laboral, la accesibilidad a servicios públicos y la renta percibida por los núcleos familiares. Por otra parte, se corrobora que las condiciones de vecindario y la recepción de transferencias monetarias corrientes tienen un poder clasificatorio reducido.The use of quantitative techniques for the classification of population segments is a critical phase to evaluate their conditions. This information will serve as input for planning strategies to alleviate poverty. In this article, we present a model of vector support machines. Consequently, a sample of families residing in Cartagena de Indias is segmented, based on certain economic and sociodemographic variables. Analytical results confirm that most important factors are employment status, accessibility to public services and familiar income. In addition, it is corroborated that neighborhood conditions and monetary transfers have a low discriminatory power.Universidad Pablo de Olavid

Core-collapse Supernovae from the Palomar Transient Factory: Indications for a Different Population in Dwarf Galaxies

We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M_r ≈ –14 mag) and including a substantial fraction (>20%) of dwarf (M_r ≥ –18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25^(+0.3)_(–0.15) and 0.23^(+0.11)_(–0.08), respectively; 1σ uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population

Design of a control charter based on principal component analysis. Acase study

El abanico de métodos y técnicas cuantitativas utilizadas para la detección de variaciones de fondo en procesos de manufactura se circunscriben en una disciplina matriz, catalogada como control estadístico de procesos. Tales métodos poseen una aptitud sobresaliente para diagnosticar el estado general de sistemas productivos y realizar una evaluación simultánea de diversas características de calidad interrelacionadas. En el marco de esta investigación, se propone el análisis y monitoreo de un proceso químico sustentado en los principios teóricos del análisis en componentes principales. De este modo, las variables originales seleccionadas son representadas en un espacio dimensional más compacto, bajo la hipótesis de normalidad multivariante. Se construye en la fase posterior, un gráfico de control basado en los cuadrados de los errores de predicción con el objeto de evaluar el comportamiento de los factores subyacentes. Los resultados indican que el proceso no es marginalmente estable y existe un margen de reducción de variabilidad significativo.The set of quantitative methods and techniques used to detect assignable variations in manufacturing processes are contained within a discipline classified as statistical process control. Such methods carry out precise evaluations on the general state of productive systems and carry out simultaneous monitoring of various interrelated quality characteristics. In the framework of this research, the analysis of a chemical process based on the theoretical principles of principal component analysis is proposed, which enables the representation of the original variables in a compact dimensional space. In the later phase, a control graph based on the squares of the prediction errors is constructed in order to evaluate the behavior of the composite variables found. The results indicate that the process is not marginally stable and it is necessary to reduce its variability margin.Universidad Pablo de Olavid

Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star

We present pre- and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHα 188-G4 and HBC 722). Prior to this outburst, LkHα 188-G4 was classified as a classical T Tauri star (CTTS) on the basis of its optical emission-line spectrum superposed on a K8-type photosphere and its photometric variability. The mid-infrared spectral index of LkHα 188-G4 indicates a Class II-type object. LkHα 188-G4 exhibited a steady rise by ~1 mag over ~11 months starting in August 2009, before a subsequent more abrupt rise of >3 mag on a timescale of ~2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (1) an increase in brightness by ≳ 4 mag, (2) a bright optical/near-infrared reflection nebula appeared, (3) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Hα which is characterized by a P Cygni profile, (4) near-infrared spectra resemble those of late K-M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H_(2)O, and (5) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHα 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified CTTS LkHα 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionis-like variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects