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Selman, Victor; Selman, Ruth Corey; Selman, Jerry; Selman, Elsie

doi:10.19030/tlc.v1i5.1944

Cited by 4 publications

(3 citation statements)

References 3 publications

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“…El enema contrastado tiene una sensibilidad del 86 % y especificidad del 90 %, con falsos negativos de hasta 20 al 28 %, por lo que si se encuentra alterado siempre es necesario ampliar los estudios. Si se sospecha enterocolitis no debe realizarse en el curso de esta por riesgo de perforación intestinal (23).…”

Section: Diagnósticounclassified

Enfermedad de Hirschsprung, un enfoque practico.

Arbeláez¹,

Posada

2022

Pediatria.

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La enfermedad de Hirschsprung fue descrita por el pediatra danés Harald Hirschsprung en 1888. Es la neuropatía entérica congénita más común, donde se produce una ausencia de relajación del musculo entérico, con posterior obstrucción intestinal. Su etiopatogenia está dada por la aganglionosis en el tracto digestivo, afectando principalmente la región rectosigmoidea. Así, manteniendo contraído el esfínter anal interno. Se clasifica en cuatro tipos: segmento corto, la más común; segmento largo, segmento ultracorto y aganglionosis coli. La clínica frecuentemente inicia en el periodo neonatal. La triada clásica consiste en distensión abdominal, ausencia de meconio en las primeras 24 a 48 horas de vida y vomito bilioso con intolerancia a la vía oral. La aproximación diagnostica se realiza mediante rayos X de abdomen, enema de contraste o manometría rectal. La prueba gold standard es la biopsia rectal, la cual se considera positiva si hay ausencia de células ganglionares en el plexo mientérico y submucoso del colon. El manejo inicial de la enfermedad se basa en resucitación con líquidos endovenosos, antibiótico de amplio espectro para prevención de enterocolitis y translocación bacteriana, descompresión con sonda nasogástrica y lavados colónicos. El tratamiento definitivo es la resección colónica del segmento afectado. Las principales complicaciones postoperatorios son: excoriación perianal, constipación, suciedad, diarrea, incontinencia fecal y enterocolitis.

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Section: Diagnósticounclassified

Enfermedad de Hirschsprung, un enfoque practico.

Arbeláez¹,

Posada

2022

Pediatria.

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“…However, in many cases, the telescope plus camera optical system may introduce variations in the FWHM of the images at the focal plane (Schroeder 2013) and even changes on the shape of the PSF (e.g., aberrations). Also, focal reducers, commonly used in wide-field imagers, can introduce illumination problems that generate background variations on scales of the field-of-view of the detector (Selman 2004). Both of these effects will have an impact on the Cramér-Rao bound, depending on the position of the source relative to the optical axis of the camera, and it is therefore important to quantify them.…”

Section: Effects Of a Variable Psf Or A Variable Backgroundmentioning

confidence: 99%

Analysis of the Cramér-Rao Bound in the Joint Estimation of Astrometry and Photometry

Mendez

Silva²,

Orostica³

et al. 2014

Publications of the Astronomical Society of the Pacific

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In this paper we use the Cramér-Rao lower uncertainty bound to estimate the maximum precision that could be achieved on the joint simultaneous (or 2D) estimation of photometry and astrometry of a point source measured by a linear CCD detector array.1 On leave at the European Southern Observatory, Casilla 19001, Santiago, Chile.-2 -We develop exact expressions for the Fisher matrix elements required to compute the Cramér-Rao bound in the case of a source with a Gaussian light profile. From these expressions we predict the behavior of the Cramér-Rao astrometric and photometric precision as a function of the signal and the noise of the observations, and compare them to actual observations -finding a good correspondence between them.From the Cramér-Rao bound we obtain the well known fact that the uncertainty in flux on a Poisson-driven detector, such as a CCD, goes approximately as the square root of the flux. However, more generally, higher order correction factors that depend on the ratio B/F or F/B (where B is the background flux per pixel and F is the total flux of the source), as well as on the properties of the detector (pixel size) and the source (width of the light profile), are required for a proper calculation of the minimum expected uncertainty bound in flux. Overall the Cramér-Rao bound predicts that the uncertainty in magnitude goes as (S/N ) −1 under a broad range of circumstances.As for the astrometry we show that its Cramér-Rao bound also goes as (S/N ) −1 but, additionally, we find that this bound is quite sensitive to the value of the backgroundsuppressing the background can greatly enhance the astrometric accuracy.We present a systematic analysis of the elements of the Fisher matrix in the case when the detector adequately samples the source (oversampling regime), leading to closed-form analytical expressions for the Cramér-Rao bound. We show that, in this regime, the joint parametric determination of photometry and astrometry for the source become decoupled from each other, and furthermore, it is possible to write down expressions (approximate to first order in the small quantities F/B or B/F ) for the expected minimum uncertainty in flux and position. These expressions are shown to be quite resilient to the oversampling condition, and become thus very valuable benchmark tools to estimate the approximate behavior of the maximum photometric and astrometric precision attainable under pre-specified observing conditions and detector properties.

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“…It is possible vignetting effects diffuse light and light being imaged from point sources differently, and the photometric flat actually corrects for this effect. Further, Selman (2004) and Anderson et al (1995) suggest that gradients in the diffuse source, scattered light in the telescope and instrument, and sky concentration produced by the focal reducer are additional possible sources of error introduced in the traditional flat-fielding process.…”

Section: Photometric Flat Fieldingmentioning

confidence: 99%

Building an Automated Telescope with High Photometric Accuracy

Grauer

Neely²,

Lacy

2008

PUBL ASTRON SOC PAC

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The NFO WebScope is a Web-based observatory which has been in use since 2004 December. The telescope is an 0.6 m Group 128 Cassegrain reflector with a new drive and control system. By optical modifications and appropriate image treatment, we have been able to reach a differential photometric accuracy of about 0.005 mag per observation in work on eclipsing binary stars. In addition, middle school, high school, college, graduate students, and public school teachers use this telescope to conduct their astronomical research projects under a NASA IDEAS grant.

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Non-Stop Mega-Fun Learning

Cited by 4 publications

References 3 publications

Enfermedad de Hirschsprung, un enfoque practico.

Enfermedad de Hirschsprung, un enfoque practico.

Analysis of the Cramér-Rao Bound in the Joint Estimation of Astrometry and Photometry

Building an Automated Telescope with High Photometric Accuracy

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