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We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505±22(stat)(-36)(+28)(syst)] mb is found.
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We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called "extragalactic" diffuse gamma-ray emission (EGB). This component of the diffuse gamma-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modeling of the bright foreground diffuse Galactic gamma-ray emission, the detected LAT sources, and the solar gamma-ray emission. We find the spectrum of the EGB is consistent with a power law with a differential spectral index gamma = 2.41 +/- 0.05 and intensity I(>100 MeV) = (1.03 +/- 0.17) x 10(-5) cm(-2) s(-1) sr(-1), where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.
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We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106{-21}{+35}) g/cm{2}/decade below 10{18.24+/-0.05} eV, and (24+/-3) g/cm{2}/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm{2}. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
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The diffuse galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission greater, > or approximately equal to 1 GeV relative to diffuse galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called "EGRET GeV excess"). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10 degrees < or = |b| < or = 20 degrees. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
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1. Cancer of the large bowel is second in cancer incidence to lung cancer in Kentucky and in the United States. It is second only to breast cancer in women. 2. It is far more common in the United States and countries with people in the higher socio-economic levels. 3. In addition to the well known associated or premalignant disease, diets high in fats and proteins are thought to increase the risk of the disease. 4. Much research is being carried on to determine other factors in the etiology of this condition. 5. The treatment of choice is still surgical removal of the lesion and all node-bearing and neighboring tissue, including the no-touch isolation technique with early ligation of the section of bowel to be removed. 6. Chemotherapy and radiation therapy are of proven value in more advanced disease. 7. Carcinoembryonic antigen is of value in the prognosis of colorectal cancer.
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Neoplasias do Colo , Neoplasias Retais , Antígeno Carcinoembrionário/análise , Neoplasias do Colo/epidemiologia , Neoplasias do Colo/etiologia , Neoplasias do Colo/terapia , Feminino , Fluoruracila/uso terapêutico , Humanos , Masculino , Prognóstico , Neoplasias Retais/epidemiologia , Neoplasias Retais/etiologia , Neoplasias Retais/terapia , Estados UnidosRESUMO
Residual impairment after alcohol consumption implies that the relationship between blood alcohol concentration (BAC) and deficits in performance of some task is not the same when becoming intoxicated as it is when returning to sobriety. A pilot study was performed to determine the feasibility of and the appropriate methodology for studies on residual impairment of smooth pursuit performance. Four subjects consumed alcohol for 2 h. Measurements of BAC and smooth pursuit eye movements were made every 30 min during drinking and for 4 h after drinking. Pursuits were elicited by having subjects track a sinusoidal target (0.40 Hz and 0.60 Hz) for 10 s. Impairment of smooth pursuit was quantified with frequency analysis scores. Frequency analysis scores declined as BAC increased. As BAC decreased, frequency analysis scores tended to increase toward pre-drink levels. The relationship between BAC and frequency analysis score was not significantly different on the ascending and descending limbs of the blood alcohol curve. However, the idea that residual impairment does not occur could not be conclusively demonstrated for several reasons. First, as BAC returned to pre-drink levels, frequency analysis scores were inconsistent for each subject perhaps because of boredom and fatigue. Second, the relationship between BAC and frequency analysis score varied between subjects. Finally, because the recording periods were short, the effect of alcohol on sustained attention could not be assessed. In this paper, potential artifacts in studies of residual impairment of pursuits are discussed and potential solutions to the methodological problems encountered in the pilot study are provided.
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Consumo de Bebidas Alcoólicas/efeitos adversos , Etanol/sangue , Transtornos da Motilidade Ocular/etiologia , Adulto , Consumo de Bebidas Alcoólicas/sangue , Análise de Variância , Estudos de Viabilidade , Humanos , Masculino , Monitorização Fisiológica/métodos , Monitorização Fisiológica/normas , Transtornos da Motilidade Ocular/diagnóstico , Transtornos da Motilidade Ocular/fisiopatologia , Projetos Piloto , Índice de Gravidade de Doença , Fatores de TempoRESUMO
Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close to ~10(15) electron volts. However, the nature of the particles that produce the emission remains ambiguous. We report observations of SNR W44 with the Fermi Large Area Telescope at energies between 2 x 10(8) electron volts and 3 x10(11) electron volts. The detection of a source with a morphology corresponding to the SNR shell implies that the emission is produced by particles accelerated there. The gamma-ray spectrum is well modeled with emission from protons and nuclei. Its steepening above approximately 10(9) electron volts provides a probe with which to study how particle acceleration responds to environmental effects such as shock propagation in dense clouds and how accelerated particles are released into interstellar space.
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The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.
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Adenocarcinoma Mucinoso , Neoplasias do Colo , Adolescente , Fatores Etários , Humanos , Metástase Linfática , MasculinoRESUMO
Microquasars are accreting black holes or neutron stars in binary systems with associated relativistic jets. Despite their frequent outburst activity, they have never been unambiguously detected emitting high-energy gamma rays. The Fermi Large Area Telescope (LAT) has detected a variable high-energy source coinciding with the position of the x-ray binary and microquasar Cygnus X-3. Its identification with Cygnus X-3 is secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. The gamma-ray emission probably originates from within the binary system, opening new areas in which to study the formation of relativistic jets.
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Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.
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Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.
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Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface.
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We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17sigma from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.
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Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m;{2} sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.
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The energy spectrum of cosmic rays above 2.5 x 10;{18} eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional, variantE;{-gamma}, at energies between 4 x 10;{18} eV and 4 x 10;{19} eV is 2.69+/-0.02(stat)+/-0.06(syst), steepening to 4.2+/-0.4(stat)+/-0.06(syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min.
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Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 x 10(-13) seconds per second. Its characteristic age of 10(4) years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.
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PURPOSE: The purpose of this study was to determine whether experience improves detection of small eye movements similar to those seen in the cover test during ideal conditions. METHODS: Three groups of examiners with varying amounts of experience in eye movement detection tasks were studied. Eight examiners were 1st-year optometry students, six were 4th-year optometry students, and six were practicing optometrists. To determine thresholds for eye movement detection, examiners indicated the horizontal direction in which the eyes of one of the experimenters moved. The direction and extent of each eye movement was randomly selected. The extent of the eye movement was one of eight logarithmic steps from a maximum that was determined through an initial session where the approximate sensitivity of the examiners was found (generally +/- 1.75 prism diopters). RESULTS: Detection thresholds were determined by fitting the data with a cumulative Gaussian function. The mean horizontal eye movement eye movement necessary to obtain 99% correct judgments was 2.65 prism diopters for the 1st-year students, 2.47 prism diopters for the 4th-year students, and 2.40 prism diopters for the practicing optometrists. CONCLUSIONS: The results indicate that during ideal conditions, little or no training is required for efficient detection of small eye movements.