Angular Correlations of the X-Ray Background and Clustering of Extragalactic X-Ray Sources

The information content of the autocorrelation function (ACF) of intensity fluctuations of the X-ray background (XRB) is analyzed. The tight upper limits set by ROSAT deep survey data on the ACF at arcmin scales imply strong constraints on clustering properties of X-ray sources at cosmological distances and on their contribution to the soft XRB. If quasars have a clustering radius r_0=12-20 Mpc (H_0=50), and their two point correlation function, is constant in comoving coordinates as indicated by optical data, they cannot make up more 40-50% of the soft XRB (the maximum contribution may reach 80% in the case of stable clustering, epsilon=0). Active Star-forming (ASF) galaxies clustered like normal galaxies, with r_0=10-12 Mpc can yield up to 20% or up to 40% of the soft XRB for epsilon=-1.2 or epsilon=0, respectively. The ACF on degree scales essentially reflects the clustering properties of local sources and is proportional to their volume emissivity. The upper limits on scales of a few degrees imply that hard X-ray selected AGNs have r_0<25 Mpc if epsilon=0 or r_0<20 Mpc if epsilon=-1.2. No significant constraints are set on clustering of ASF galaxies, due to their low local volume emissivity. The possible signal on scales >6 deg, if real, may be due to AGNs with r_0=20 Mpc; the contribution from clusters of galaxies with r_0~50 Mpc is a factor 2 lower.Comment: ApJ, in press (20 July 1993); 28 pages, TeX, ASTRPD-93-2-0

Evaluación de las formulaciones de película comestible de Nostoc sphaericum aplicadas a la conservación de fresas

The high perishability rate in strawberries (Fragaria x ananassa) complicates their post-harvest storage, creating the need to develop effective means of preservation. The research studied the physicochemical qualities of strawberries coated with edible films based on Nostoc (Nostoc Sphaericum). The films were generated by immersing the fruit in solutions of Nostoc polysaccharides at 0,7% (A), 1,0% (B) and 1,3% (C) concentration (p/v). The product was stored for 8 days at room temperature (18 ± 2 ° C), subsequently the quality parameters were measured. The DBCA design was applied with a significance level of 5%. The texture was found to vary directly with the polysaccharide concentration in the coating. The average weight loss for treatments A, B, C and the pattern were 66,92%, 60,92%, 49,06% and 41,72%, respectively. In all cases, a variation of less than 0,3 was observed in the pH scale and greater than 0,3% for acidity, without significant differences. The variation in SST for the treatments was 4,9 (C), 5,2 (A) and 7,4 (B) ° brix. An extension of the useful life of 16% of strawberries up to two days was determined. It was determined that the application of Nostoc films prolong the useful life of strawberries, highlighting their performance in weight loss and texture compared to the control sample, on the descending scale C&gt; B&gt; A.La alta tasa de perecibilidad en fresas (Fragaria x ananassa) complica su almacenamiento postcosecha, surgiendo la necesidad de desarrollar medios de conservación eficaces. En la investigación se estudiaron las cualidades físicoquímicas de fresas recubiertas con películas comestibles a base de Nostoc (Nostoc Sphaericum). Las películas se generaron al sumergir el fruto en soluciones de polisacáridos de Nostoc al 0,7 % (A), 1,0 % (B) y 1,3 % (C) de concentración (p/v). El producto se almacenó durante 8 días a temperatura ambiente (18 ± 2 °C), posteriormente se midieron los parámetros de calidad. Se aplicó el diseño DBCA con nivel de significancia 5%. Se determinó que la textura varía directamente con la concentración de polisacárido en la cobertura. La pérdida promedio de peso para los tratamientos A, B, C y el control fueron 66,92%, 60,92%, 49,06% y 41,72%, respectivamente. En todos los casos se observó una variación inferior a 0,3 en la escala de pH y superior al 0,3% para la acidez, sin diferencias significativas. La variación en SST para los tratamientos fue de 4,9 (C), 5,2 (A) y 7,4 (B) °brix. Se determinó una extensión de la vida útil del 16% de fresas&nbsp; hasta dos días. Se determinó que la aplicación de películas de Nostoc prolongan la vida útil de fresas, resaltando su desempeño en la pérdida de peso y textura frente a la muestra control, en la escala descendiente C &gt; B &gt; A

Small-Scale Fluctuations in Cosmic X-ray Background : A Power Spectrum Approach

Equations to investigate fluctuations in cosmic X-ray background radiation due to point-like sources at high-redshift are formulated in a systematic way. The angular power spectrum of X-ray background fluctuations is investigated from large-scales to small-scales in various cosmological models such as open universe models and models with the cosmological constant, assuming a simple evolution model of the sources. The effect of epoch-dependent bias is demonstrated for small-angle fluctuations. The contribution from shot noise fluctuations is also discussed.Comment: 12 pages, 4 figures, Phys.Rev.D in pres

The nature of the unresolved extragalactic soft CXB

In this paper we investigate the power spectrum of the unresolved 0.5-2 keV CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal which, on scales >30", is significantly higher than the Shot-Noise and is increasing with the angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like AGN, Galaxies and Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall, our modeling predicts that \sim 20% of the unresolved CXB flux is made by low luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic Medium). We do not find any direct evidence of the so called Warm Hot Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast {\delta} <1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit to the space density of postulated X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution models.Comment: 15 pages, 9 figures, accepted by MNRA

The ROSAT International X-ray/Optical Survey (RIXOS): source catalogue

We describe the ROSAT International X-ray/Optical Survey (RIXOS), a medium-sensitivity survey and optical identification of X-ray sources discovered in ROSAT high Galactic latitude fields (|b|>28°) and observed with the Position Sensitive Proportional Counter (PSPC) detector. The survey made use of the central 17 arcmin of each ROSAT field. A flux limit of 3×10−14 erg cm−2 s−1 (0.5–2 keV) was adopted for the survey, and a minimum exposure time of 8000 s was required for qualifying ROSAT observations. X-ray sources in the survey are therefore substantially above the detection threshold of each field used, and many contain enough counts to allow the X-ray spectral slope to be estimated. Spectroscopic observations of potential counterparts were obtained of all sources down to the survey limit in 64 fields, totalling a sky area of 15.77 deg2. Positive optical identifications are made for 94 per cent of the 296 sources thus examined. A further 18 fields (4.44 deg2), containing 105 sources above the 3×10−14 erg cm−2 s−1 survey limit, are completely optically identified to a higher flux of 8×10−14 erg cm−2 s−1 (0.5–2 keV). Optical spectroscopic data are supplemented by deep CCD imaging of many sources to reveal the morphology of the optical counterparts, and objects too faint to register on Sky Survey plates. The faintest optical counterparts have R∼22. This paper describes the survey method, and presents a catalogue of the RIXOS sources and their optical identifications. Finding charts based on Sky Survey data are given for each source, supplemented by CCD imaging where necessary

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM