The extragalactic background light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation ...from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the Delta *g-ray flux of extragalactic sources such as blazars and gamma-ray bursts (GRBs). The Large Area Telescope on board Fermi detects a sample of Delta *g-ray blazars with redshift up to z ~ 3, and GRBs with redshift up to z ~ 4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of Delta *g-ray flux attenuation by the EBL. We place upper limits on the Delta *g-ray opacity of the universe at various energies and redshifts and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the 'baseline' model of Stecker et al. can be ruled out with high confidence.
We report the detection of high-energy Delta *g-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady ...point-like emission above 200 MeV has been detected at significance levels of 6.8 Delta *s and 4.8 Delta *s, respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with Delta *g-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and Delta *g-ray emission in star-forming galaxies.
Vaccination has been among the greatest contributors to the past century's dramatic improvements in health and life expectancy. Recent advances in vaccinology have resulted in new vaccines that will ...likely lead to substantial future health gains. However, the high cost of these new vaccines, such as the human papillomavirus (HPV) vaccine, poses an obstacle to their widespread adoption in many countries. Economic evaluation can help to determine if investment in vaccine introduction is worthwhile. However, existing economic evaluations usually focus on a narrow set of vaccination-mediated benefits—most notably avoided medical-care costs—and fail to account for several categories of potentially important gains. We consider three sources of such benefit and discuss them with respect to HPV vaccination: (i) outcome-related productivity gains, (ii) behaviour-related productivity gains, and (iii) externalities. We also highlight that HPV vaccination protects against more than just cervical cancer and that these other health gains should be taken into account. Failing to account for these broader benefits of HPV vaccination could result in substantial underestimation of the value of HPV vaccination, thereby leading to ill-founded decisions regarding its introduction into national immunization programmes.
We report the discovery of high-energy (E > 100 MeV) gamma -ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made ...with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the gamma -ray source is only 3' away from the NGC 1275 nucleus, well within the 95% LAT error circle of 5'. The spatial distribution of gamma -ray photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F gamma = (2.10 - 0.23) X 10-7 ph (>100 MeV) cm-2 s-1 and Gamma = 2.17 - 0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period. Previous EGRET observations gave an upper limit of F gamma < 3.72 X 10-8 ph (>100 MeV) cm-2 s-1 to the gamma -ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous and historical radio observations are also reported. The broadband spectrum of NGC 1275 is modeled with a simple one-zone synchrotron/synchrotron self-Compton model and a model with a decelerating jet flow.
This study explored the relationship between cultural leisure activities, recovery experiences and two outcomes among hospital workers. The differences in recovery experiences (detachment, ...relaxation, mastery and control) and outcomes (work engagement and subjective recovery state) among hospital personnel (N=769) were analysed by the type (receptive or creative) and frequency of cultural activities. The cross-sectional data were collected by a digital questionnaire. Employees who reported both receptive and creative cultural leisure activities on a weekly basis had the highest relaxation, mastery and control experiences during off-job time. In addition, those with weekly creative activities had beneficial mastery experiences. There were no differences in recovery outcomes after adjustment for age, except in work engagement. Cultural leisure activities, and creative activities in particular, play an important role in certain aspects of recovery.
This paper presents the first results from the observations of LS I +61°303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results ...indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 ± 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 ± 0.03(stat) ± 0.07(syst) 10–6 ph cm–2 s–1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index Γ = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. Finally, this and the energy cutoff seen with Fermi suggest that the link between HE and VHE gamma rays is nontrivial.
Microtubule assembly in Saccharomyces cerevisiae is initiated from sites within spindle pole bodies (SPBs) in the nuclear envelope. Microtubule plus ends are thought to be organized distal to the ...SPBs, while minus ends are proximal. Several hypotheses for the function of microtubule motor proteins in force generation and regulation of microtubule assembly propose that assembly and disassembly occur at minus ends as well as at plus ends. Here we analyse microtubule assembly relative to the SPBs in haploid yeast cells expressing green fluorescent protein fused to alpha-tubulin, a microtubule subunit. Throughout the cell cycle, analysis of fluorescent speckle marks on cytoplasmic astral microtubules reveals that there is no detectable assembly or disassembly at minus ends. After laser-photobleaching, metaphase spindles recover about 63% of the bleached fluorescence, with a half-life of about 1 minute. After anaphase onset, photobleached marks in the interpolar spindle are persistent and do not move relative to the SPBs. In late anaphase, the elongated spindles disassemble at the microtubule plus ends. These results show for astral and anaphase interpolar spindle microtubules, and possibly for metaphase spindle microtubules, that microtubule assembly and disassembly occur at plus, and not minus, ends.
We present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard ...Fermi-LAT Sources (3FHL), containing 1556 objects characterized in the 10 GeV-2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (z > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5 × 10−11 ph cm−2 s−1, respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ-ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. Furthermore, we estimate that for the same flux limit of 10−12 erg cm−2 s−1, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.
With a single microtubule attachment, budding-yeast kinetochores provide an excellent system for understanding the coordinated linkage to dynamic microtubule plus ends for chromosome oscillation and ...positioning. Fluorescent tagging of kinetochore proteins indicates that, on average, all centromeres are clustered, distinctly separated from their sisters, and positioned equidistant from their respective spindle poles during metaphase. However, individual fluorescent chromosome markers near the centromere transiently reassociate with their sisters and oscillate from one spindle half to the other. To reconcile the apparent disparity between the average centromere position and individual centromere proximal markers, we utilized fluorescence recovery after photobleaching to measure stability of the histone-H3 variant Cse4p/CENP-A. Newly synthesized Cse4p replaces old protein during DNA replication. Once assembled, Cse4-GFP is a physically stable component of centromeres during mitosis. This allowed us to follow centromere dynamics within each spindle half. Kinetochores remain stably attached to dynamic microtubules and exhibit a low incidence of switching orientation or position between the spindle halves. Switching of sister chromatid attachment may be contemporaneous with Cse4p exchange and early kinetochore assembly during S phase; this would promote mixing of chromosome attachment to each spindle pole. Once biorientation is attained, centromeres rarely make excursions beyond their proximal half spindle.
The detection of diffuse radio emission associated with clusters of galaxies indicates populations of relativistic leptons infusing the intracluster medium (ICM). Those electrons and positrons are ...either injected into and accelerated directly in the ICM, or produced as secondary pairs by cosmic-ray ions scattering on ambient protons. Radiation mechanisms involving the energetic leptons together with the decay of neutral pions produced by hadronic interactions have the potential to produce abundant GeV photons. Here, we report on the search for GeV emission from clusters of galaxies using data collected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope from 2008 August to 2010 February. Thirty-three galaxy clusters have been selected according to their proximity and high mass, X-ray flux and temperature, and indications of non-thermal activity for this study. We report upper limits on the photon flux in the range 0.2-100 GeV toward a sample of observed clusters (typical values (1-5) x 10(-9) photon cm(-2) s(-1)) considering both point-like and spatially resolved models for the high-energy emission and discuss how these results constrain the characteristics of energetic leptons and hadrons, and magnetic fields in the ICM. The volume-averaged relativistic-hadron-to-thermal energy density ratio is found to be <5%-10% in several clusters.
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