Abstract
The Large Area Telescope (LAT), the primary instrument for the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering ...the energy range from 30 MeV to more than 300 GeV. We describe the performance of the instrument at the 10 yr milestone. LAT performance remains well within the specifications defined during the planning phase, validating the design choices and supporting the compelling case to extend the duration of the Fermi mission. The details provided here will be useful when designing the next generation of high-energy gamma-ray observatories.
The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new {gamma}-ray observatories. We report here on initial Fermi Large Area Telescope ...observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E {>=} 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of {gamma} = 1.51{sup +0.05} {sub -0.04} with an exponential cutoff at E{sub c} = 2.9 {+-} 0.1 GeV. Spectral fits with generalized cutoffs of the form e{sup -(E/E{sub c}){sup b}} require b {<=} 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.
The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope began its on--orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization ...of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.
The GLAST LAT tracker construction and test Belli, F.; Andreanelli, L.; Angelini, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2007, Letnik:
570, Številka:
2
Journal Article
Recenzirano
GLAST is a next generation high-energy gamma-ray observatory designed for making observations of celestial gamma-ray sources in the energy band extending from 10
KeV to more than 300
GeV. Respect to ...the previous instrument EGRET, GLAST will have a higher effective area (six times more), higher field of view, energy range and resolution, providing an unprecedented advance in sensitivity (a factor 30 or more). The main scientific goals are the study of all gamma-ray sources such as blazars, gamma-ray bursts, supernova remnants, pulsars, diffuse radiation, and unidentified high-energy sources. The construction and test of the Large Area Telescope (LAT) tracker, has been a great effort during the past years, involving tens of people from many Italian INFN sections and industrial partners. Environmental and performance tests of the hardware, detectors and reading electronics, have been carried on during all the steps of the LAT construction. The resulting LAT performance are better than the ones required by the original science proposal, demonstrating the quality of the italian group effort. In this article we summarize the LAT construction and test workflow, presenting its main results.
Qualitative/quantitative phytochemical variations were observed in dried flowering tops of cultivated Hypericum perforatum L. cv. Zorzi infected by phytoplasmas of the "ash yellows" class, identified ...by direct and nested polymerase chain reaction (PCR); this is the first report of ribosomial group 16SrVII phytoplasmas in St. John's Wort. Methanolic extracts of healthy and infected plants were separated by reversed phase high-performance liquid chromatography to quantify naphthodianthrones and flavonoids, while essential oils were analyzed by means of gas chromatography (GC)-GC/MS. The affected plants exhibited decreased amounts of rutin (1.96 +/- 0.23 vs 4.96 +/- 0.02 mg/g), hyperoside (2.38 +/- 0.21 vs 3.04 +/- 0.05 mg/g), isoquercitrin (1.47 +/- 0.04 vs 3.50 +/- 0.08 mg/g), amentoflavone (0.12 +/- 0.01 vs 0.39 +/- 0.02 mg/g), and pseudohypericin (1.41 +/- 0.23 vs 2.29 +/- 0.07 mg/g), whereas the chlorogenic acid content was doubled (1.56 +/- 0.11 vs 0.77 +/- 0.02 mg/g). Hypericin, quercitrin, and quercetin contents were not severely affected. The essential oil yield was drastically reduced in infected material (0.11 vs 0.75% in healthy material) and revealed an increased abundance of sesquiterpenes (beta-caryophyllene, delta-elemene, and germacrene D, in particular) and a matching decrease in monoterpene hydrocarbons and aliphatics. The consequences that the phytopathological condition of cultivated H. perforatum plants has on the commercial quality, market value, and therapeutic efficacy are outlined.
Background Overviews of trials suggest that percutaneous transluminal coronary angioplasty (PTCA) may be more effective than thrombolysis. However, whether these effects are sustained beyond hospital ...discharge, and the extent to which the results are applicable to a broad cross section of patients and the wider community are unknown. We compared the effectiveness of primary PTCA and thrombolysis in acute myocardial infarction during a 6-month follow-up period.
Methods Detailed individual patient data were collected from randomized trials commenced from 1989 to 1996 that compared primary PTCA with thrombolysis. Data were combined to produce estimates of relative reduction in events at 30 days and 6 months for the group and for predefined clinical subgroups. Treatment effects were also assessed in relation to several study-related factors.
Results Eleven trials were identified. The mortality rate at 30 days was 4.3% for 1348 patients randomized to undergo PTCA, and 6.9% for 1377 patients assigned to thrombolytic therapy (relative risk RR 0.62, 95% CI 0.44-0.86,
P = .004). At 6 months, the mortality rate was 6.2% for PTCA and 8.2% for thrombolysis (RR 0.73, 95% CI 0.55-0.98,
P = .04). Combined death and reinfarction rates at 30 days were 7.0% for PTCA and 12.9% for thrombolysis, with a sustained effect at 6 months (RR 0.60, 95% CI 0.48-0.75,
P < .0001). The risk of hemorrhagic stroke at 30 days was lower in the PTCA group (RR 0.06, 95% CI 0.0-0.50,
P = .009). The relative treatment effect did not vary across clinically important subgroups, but the absolute benefit varied according to baseline risk. The relative treatment effect varied across the trials and according to the thrombolytic comparator used, the delay in performing PTCA, and the recruitment rate.
Conclusion In the context of these trials, primary PTCA was more effective than thrombolytic therapy in reducing death, reinfarction, and stroke, with the greatest absolute benefit in patients who were at the highest risk. These benefits appear to be sustained for 6 months. The effect of treatment varied significantly across the trials, and this raises issues about how widely the results can be applied. (Am Heart J 2003;145:47-57.)
Grindelia robusta (Asteraceae), a perennial species native to California, is exploited pharmaceutically because of the anti-tussive, expectorant, sedative, and analgesic effects of its essential oil ...fractions. During spring 2007, phytoplasmas belonging to subgroup 16SrI-B (Aster yellows, Candidatus Phytoplasma asteris) were identified in G. robusta plants showing virescence and phyllody symptom, growing in the Herb Garden of Casola Valsenio (Ravenna, Italy). To determine whether qualitative differences existed in the composition of essential oils between healthy and phytoplasma-infected plants, gas chromatography-mass spectrometry (GC-MS) analyses were performed. Samples collected from six symptomatic and five symptomless plants were tested by nested PCR followed by RFLP analysis. Ca. P. asteris was found only in symptomatic samples. Oils from healthy ("H") and infected ("I") samples obtained by direct steam distillation of 0.5 kg dried plant material were submitted to GC-MS analyses, according to recendy described methodologies (Bruni et al., 2007). About 42 different components were separated and identified in the analyzed samples. A higher percentage of selected monoterpenes was observed in oil "I" as compared with "H". In particular, the concentration of limonene and borneol acetate was almost 50% higher, and that of borneol was 15% in "H" as compared with 21.3% in "I". These preliminary results confirm previous findings relative to Hypericum perforatum infected by the ash yellows phytoplasma, in which qualitative and quantitative differences in oil composition were detected (Bruni et al, 2005). Phytoplasma infections appear to modify also metabolic pathways in other plant species such as apple, in which Candidatus Phytoplasma mali, the apple proliferation agent, influences the behaviour of insect vectors and enhances disease transmission (Mayer et al., 2008).
The embryonic heart precursors of Drosophila are arranged in a repeated pattern of segmental units. There is growing evidence that the development of individual elements of this pattern depends on ...both mesoderm intrinsic patterning information and inductive signals from the ectoderm. In this study, we demonstrate that two homeobox genes, ladybird early and ladybird late, are involved in the cardiogenic pathway in Drosophila. Their expression is specific to a subset of cardioblast and pericardial cell precursors and is critically dependent on mesodermal tinman function, epidermal Wingless signaling and the coordinate action of neurogenic genes. Negative regulation by hedgehog is required to restrict ladybird expression to two out of six cardioblasts in each hemisegment. Overexpression of ladybird causes a hyperplasia of heart precursors and alters the identity of even-skipped-positive pericardial cells. Loss of ladybird function leads to the opposite transformation, suggesting that ladybird participates in the determination of heart lineages and is required to specify the identities of subpopulations of heart cells. We find that both early Wingless signaling and ladybird-dependent late Wingless signaling are required for proper heart formation. Thus, we propose that ladybird plays a dual role in cardiogenesis: (i) during the early phase, it is involved in specification of a segmental subset of heart precursors as a component of the cardiogenic tinman-cascade and (ii) during the late phase, it is needed for maintaining wingless activity and thereby sustaining the heart pattern process. These events result in a diversification of heart cell identities within each segment.
A rhabdovirus inducing vein yellowing in croton Bertaccini, A; Bellardi, M.G. (Istituto di Patologia Vegetale, Universita di Bologna, via F. Re, 8, 40126 Bologna (Italy))
Plant Pathology (United Kingdom),
(1992), Letnik:
41, Številka:
1
Publication
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